Section 9: Laminar flows and transition - GAMM 2012

Section 9: Laminar flows and transition 1 

Section 9: Laminar flows and transition 

Organizers: Suad Jakirlic (TU Darmstadt), Ulrich Rist (Universität Stuttgart) 

S9.1: Laminar flows and transition I Tue, 13:30–15:30 

Chair: Suad Jakirlic, Ulrich Rist S1|01–A2 

Transition Prediction and Modeling in External Flows Using RANS-based CFD Codes 

Andreas Krumbein, Normann Krimmelbein, Cornelia Seyfert (DLR Göttingen) 

Besides wind tunnel testing and flight tests, CFD simulation based on RANS solvers has become 

a standard design approach in industry for the design of aircraft. For the design point of aircraft 

a positive assessment of the numerical results was achieved for many validation and application 

tests and the prediction capabilities of the software tools could be positively evaluated. As 

a consequence, high confidence in numerical simulations could be achieved in industry and will 

eventually allow more simulation and less physical testing. However, and despite of the progress 

that has been made in the development and application of RANS-based CFD codes, there is still 

the need for improvement, for example, with regard to the capability of a proper capturing of all 

relevant physical phenomena. This can only be achieved if capable and accurate physical models 

are available in the codes. On the one hand, the combined use of turbulence and transition models 

is indispensable for flows exhibiting separation, because otherwise the close interaction between 

the laminar-turbulent transition and its impact on flow separation is not reproduced. On the other 

hand, it is not possible to fully exploit the high potential of todays advanced turbulence models 

if transition is not taken into account. Thus, in modern high-fidelity CFD codes a robust transition 

prediction and modeling must be established together with reliable and effective turbulence 

models. 

At DLR, the RANS codes for external flows, [1]-[2], have been provided with transition prediction 

and modeling functionalities which can be applied to three-dimensional aircraft configurations. 

Two different basic approaches are currently at hand: the streamline based and the transport 

equation approach. 

The streamline based approach uses information from the current flow solution along defined 

integration paths in order to compute the laminar boundary layers, either using a laminar 

boundary-layer method or by direct extraction from the RANS solution. A fully automated, local 

linear stability code analyses the laminar boundary layers and detects transition due to Tollmien- 

Schlichting or cross flow instabilities. The stability code, which applies the e N -method, [3]-[4], and 

the two N factor approach, [5], for the determination of the transition points, uses a frequency estimator 

for the detection of the relevant regions of amplified disturbances for Tollmien-Schlichting 

instabilities and a wave length estimator for cross flow instabilities. Also separation induced transition 

is covered. Alternatively, different empirical transition criteria for streamwise and crossflow 

transition are available and, in addition, criteria for attachment-line and by-pass transition. Using 

this approach transition is predicted either along spanwise line-in-flight cuts through a wing or 

along the boundary-layer edge streamline. The latter is the only possible way in the case of fully 

three-dimensional flow about fuselages or nacelles. The streamline approach has been validated 

by numerous test cases and is the standard transition prediction approach currently used in production 

simulation. Here, it is usually applied in parallel mode on large compute cluster systems, 

[6]. 

The transport equation approach, [7], is relatively new and based exclusively on local variables 

so that it is inherently parallelizable and, thus, very well suited for unstructured CFD codes and

2 Section 9: Laminar flows and transition 

large applications which can only be tackled by massively parallel computations. The boundarylayer 

quantities are resolved by the RANS computational grid and approximated by the modeling 

approach reflected by two transport equations. The prediction of the locations of transition onset 

is based on empirical criteria which can and must be evaluated locally. While the original model 

formulation was restricted to the prediction of streamwise transition mechanisms the model is 

currently extended in order to predict crossflow transition, [8]. 

The two different approaches and methods will be presented and explained, their applicability 

ranges are discussed and numerical results are compared to a number of validation test cases demonstrating 

the prediction accuracy of the different methods. The results from the application of 

the methods to large and partially very complex, industrial configurations are presented and discussed. 

Eventually, an outlook is given to the challenges placed by complex aircraft configurations 

and to the way forward to tackle the still open issues. 

[1] Krumbein, A., Automatic Transition Prediction and Application to Three-Dimensional Wing 

Configurations, Journal of Aircraft, Vol. 44, No. 1, 2007, pp. 119-133; also: AIAA Paper 

2006-914, January 2006. 

[2] Krimmelbein, N., Radespiel, R., Transition prediction for three-dimensional flows using parallel 

computation, Computers Fluids, No. 38, Elsevier, 2009, pp. 121-136, doi:10.1016/j.compfluid.2008. 

01.004. 

[3] Smith, A.M.O., Gamberoni, N., Transition, Pressure Gradient and Stability Theory, Douglas 

Aircraft Company, Long Beach, Calif. Rep. ES 26388, 1956. 

[4] van Ingen, J.L., A suggested Semi-Empirical Method for the Calculation of the Boundary 

Layer Transition Region, University of Delft, Dept. of Aerospace Engineering, Delft, The 

Netherlands, Rep. VTH-74, 1956. 

[5] Rozendaal, R. A., Natural Laminar Flow Flight Experiments on a Swept Wing Business 

Jet-Boundary-Layer Stability Analysis, NASA CP 3975, March 1986. 

[6] Krimmelbein, N., Krumbein, A., Automatic Transition Prediction for Three-Dimensional 

Configurations with Focus on Industrial Application, AIAA-2010-4292, 40th AIAA Fluid 

Dynamics Conference and Exhibit, June 28 July 1, 2010, Chicago, Illinois, USA. 

[7] Langtry, R.B., Menter, F.R., Correlation-Based Transition Modeling for Unstructured Parallelized 

Computational Fluid Dynamics Codes, AIAA Journal, Vol. 47, No.12, 2009, pp. 

2894-2906, DOI: 10.2514/1.42362. 

[8] Seyfert, C., Krumbein, A., Correlation-Based Transition Transport Modeling for Three- 

Dimensional Aerodynamic Configurations, to be presented as AIAA paper at the 50th 

Aerospace Sciences Meeting, 9-12 January 2012, Nashville, Tennessee, USA. 

Preliminary results of the conditional analysis of wall friction during laminarturbulent 

transition of a rough wall boundary layer 

Pavel Jonás, Ondřej Hladík, Oton Mazur, Václav Uruba (Czech Academy of Sciences Praha) 

The transitional intermittency is investigated in the zero pressure gradient boundary layer developing 

on the surface covered with sand paper (grits 60). The free stream mean velocity is 5 m/s 

and the turbulence level is either 0.3 percent or risen by means of the square mesh plane grid to 

3 percent and the dissipation length parameter 3.8 mm.


Records (25 kHz, 750000 samples, 16 bit) of the instantaneous wall friction in various locations 

are evaluated from the records of the single wall wire CTA output signal. The procedure of the 

constant temperature anemometer signal transformation to the wall friction has been developed 

formerly and presented in [1, 2]. The adjustment of this procedure to rough surface conditions 

is based on the mean wall friction distribution which has been determined in advance. This 

procedure is described in the paper. 

Then the transitional intermittency factor distribution is derived by means of the TERA 

method [3]. Next the conditional analysis of the wall friction records is done which sorts the wall 

friction records in passages with the non-turbulent structure (intermittency factor g = 0) and 

those with the full turbulent structure (g = 1). 

Evaluated are the probability density function and the conditioned probability density functions 

of the wall friction, relevant moments and the mean residence time of the wall friction in 

laminar and turbulent state. Results are compared with analogous characteristics received during 

investigations of smooth wall boundary layers. 

[1] Jonás, P. - Mazur, O. - Uruba, V. (1999) Statistical characteristics of the wall friction in a 

flat plate boundary layer through by-pass transition. ZAMM 79, S3, S691-S692. 

[2] Jonás, P. - Mazur, O. - Uruba, V. (2002) Problem of the intermittency distributions in 

transitional boundary layers under flows with various scales of turbulence. PAMM, Proc. 

Appl. Math. Mech. 1, Section 10.5, 298-299. 

[3] Zhang, D.H. - Chew, Y.T. - Winoto, S.H.: (1996) Investigation of intermittency measurement 

methods for transitional boundary, Exp. Thermal and Fluid Sci. 12, 433-443. 

Velocity and shear stress distributions in laminar-turbulent transition of unsteady 

boundary layer on aerofoil in high accelerating and decelerating fluid flow 

Decan J. Ivanovic, Vladan M. Ivanović (University of Montenegro, Podgorica) 

The corresponding equations of unsteady boundary layer, by introducing the appropriate variable 

transformations, momentum and energy equations and similarity parameters set, being transformed 

into generalized form. These parameters are expressing the influence of the outer flow velocity 

and the flow history in boundary layer, on the boundary layer characteristics. Since the generalized 

equation contain summ of terms equal to the number of parameters, it is necessary to limit 

the number of parameters for numerical integration. The numerical integration of the generalized 

equation with boundary conditions has been performed by means of the difference schemes and 

by using Tridiagonal Algorithm Method with iterations in the two once localized approximation, 

where the first unsteady and dynamic parameter will remaine, while all others will be let to be 

equal to zero, and where the derivatives with respect to the first unsteady parameter will be 

considered equal to zero. So obtained generalized solutions are used to calculate the distributions 

of velocity and shear stress in laminar-turbulent transition of unsteady incompressible boundary 

layer on aerofoil, whose center velocity changes in time as a degree function. It’s found that for 

both in confuser and in diffuser aerofoil regions the decelerating flow reduces the shear stress and 

favours the separation of flow, which occurring for lower contour values. The accelerating fluid 

flow postpones the boundary layer separation, i.e. laminar-turbulent transition, and vice versa 

the separation is occurring for greater contour values of aerofoil. Boundary layer characteristics 

are found directly, no further numerical integration of momentum equation.


Unsteady convective diffusion of a solute in a Hagen-Poiseuille flow through a tube 

with permeable wall 

Alexandru Dumitrache, Florin Frunzulica (POLITEHNICA University of Bucharest and Institute 

of Mathematical Statistics and Applied Mathematics) 

Effects of Interphase Mass Transfer (IMT) on the unsteady convective diffusion in a fluid flow 

through a tube surrounded by a porous medium is examined against the background of no IMT. 

The three coefficients namely exchange coefficient, convection coefficient, and dispersion coefficient 

are evaluated asymptotically at large-time using Gill Sankarasubramanian model [1]. The 

exchange coefficient exists due to IMT. 

The convective diffusion equation and the corresponding initial and boundary conditions are 

used for the beginning 

∂C 

∂t 

+ u(r)∂C 

∂x 

2 ∂ C 1 

= D + 

∂x2 r 

 

∂ 

r 

∂r 

∂C 

 

∂r 

(1) 

C(0, x, r) = F (x, r) (2) 

C(t, ∞, r) = 0 = ∂C 

(t, ∞, r) (3) 

∂r 

−D ∂C 

∂r (t, x, r) = KsC at r = ±R. (4) 

where D is the molecular diffusivity and Ks is the rate of mass transfer of solute at the walls of 

the cylinder. The condition (3) means that solute does not reach distances far down stream. The 

condition (4) implies that the flux of concentration at the walls is due to a first order chemical 

reaction. 

Then the dimesionless parameters will be used to transform equation. 

The convection and dispersion coefficient of solute are studied as a function of slip parameter, 

IMT parameter and porous parameter. All-time analysis is made analytically when there is no 

IMT. The mean concentration distribution is measured at a point inside and outside the slug. 

The peak of mean concentration is higher than that of pure convection and it is further enhanced 

with increase of porous parameter (or decrease of particle size). 

The results have applications in heat exchangers, petroleum and chemical engineering problems, 

chromatography and biomechanical problems. 

[1] R. Sankarasubramanian and W. N. Gill, Unsteady convective diffusion with interphase 

mass transfer, Proc. Roy. Soc. London A, 333 pp. 115–132, 1973. 

On the Optimum Efficiency of a Flapping Foil And Its Application to Valveless Pumps 

Markus Müllner (TU Wien) 

Several different working principles exist to drive a valveless pump. An efficient pump may be 

constructed by placing a flapping foil into a channel. For the case of inviscid flow, the pressure 

difference along the channel is equivalent to the thrust force acting on the propulsor. The effect 

of the channel walls on the forces is briefly discussed. The focus in this talk is on the determination 

of movements of highest propulsive efficiency for a given thrust. In order to treat the


optimization problem analytically, the case of a slender foil placed in a free stream, flapping in 

time-harmonic motion with small deflections, is investigated. Novel results for the heaving- and 

pitching amplitude and for the pivot point of the pitching motion are presented as a function 

of the reduced frequency σ. A surprising outcome is that for a certain range of the thrust force, 

the reduced frequency needs to be infinitely large to obtain maximum efficiency. Unfortunately, 

the optimum movements are accompanied by some drawbacks. An important issue is to reduce 

the lateral forces acting on the structure. Therefore, foil movements with zero lateral force are 

investigated and the deficit in efficiency is compared to the optimum foil motion. Furthermore, 

instead of the foil, an undulating wave motion is considered. The analytic result for different wave 

numbers k is presented and the efficiency is compared to the optimum solution of the foil. 

S9.2: Laminar flows and transition II Tue, 16:00–18:00 

Chair: Ulrich Rist, Suad Jakirlic S1|01–A2 

Global flow instabilities in plane sudden expansions 

Hendrik Christoph Kuhlmann , Daniel Lanzerstorfer (TU Wien) 

The three-dimensional linear stability of the two-dimensional, incompressible flow in a plane symmetric 

sudden expansion is considered. The geometry is varied systematically, covering expansion 

ratios (steps to outlet height) from 0.25 to 0.95. The stability analysis reveals that the primary 

symmetry-breaking bifurcation is two-dimensional. The asymmetric flow solution, however, becomes 

unstable to different secondary three-dimensional instabilities. The critical modes depend on 

the expansion ratio. An energy-transfer analysis is used to understand the nature of the instabilities. 

In the limit of vanishing step height, the critical mode is stationary and the amplification 

process is caused by a shear instability. For high expansion ratios, the basic jet-like flow and 

becomes unstable due to centrifugal forces leading to an oscillatory mode. For intermediate expansion 

ratios, an elliptic instability mechanism is identified and the instability characteristics 

change continuously with the expansion ratio. For an asymmetric geometry the disconnected 

primary solution branches are readily shifted to very high Reynolds numbers. The connected twodimensional 

solution branch is found to be very similar to the asymmetric flow of the symmetric 

channel thus showing the same type of secondary instability. 

Connecting the dots: Symmetry Analysis in Linear Stability Theory of a Linear Shear 

Flow 

Andreas Nold, Martin Oberlack (TU Darmstadt) 

A novel self-similar base solution for linear stability analysis of an unbounded linear shear flow 

employing symmetry methods is presented. Symmetry analysis is used to derive a full classification 

of symmetries of the linearized Navier-Stokes-Equations for two-dimensional perturbations 

of a linear shear flow. It is shown that the normal mode approach leading to the Orr-Sommerfeld 

equation and the Kelvin mode approach are both special classes of self-similar ansatz functions 

systematically derived in the framework of symmetry analysis. A third novel class of ansatz 

functions is presented. In the viscous case, known solutions of the initial value problem can be 

recovered by superposition of the novel self-similar modes. In the inviscid case, a new closed-form 

solution of traveling, energy-conserving modes localized in spanwise direction is presented. 

An Exact Navier-Stokes Solution for Three-Dimensional, Spanwise-Homogeneous 

Boundary Layers 

M. O. John, D. Obrist, L. Kleiser (ETH Zürich)


In some boundary layer flows the incompressible Navier-Stokes equations are amenable to exact 

similarity solutions. Two such cases are the plane stagnation flow onto a wall (Hiemenz boundary 

layer, HBL) and the asymptotic suction boundary layer flow (ASBL) over a flat wall. The Hiemenz 

solution has been extended to the swept Hiemenz configuration by superposition of a third, 

spanwise-homogeneous sweep velocity. This solution, however, becomes singular as the chordwise, 

tangential base flow component vanishes. Similarly, the ASBL does not contain any chordwise 

velocity. 

This work presents a generalized three-dimensional similarity solution, using a novel similarity 

coordinate. The HBL and ASBL are shown to be two limits of this solution which describes threedimensional 

spanwise-homogeneous impinging boundary layers at arbitrary wall-normal suction 

velocities. 

Further extensions may consist of oblique impingement, or different boundary suction directions, 

such as slip walls or stretching walls. 

Near critical laminar flow past an expansion ramp 

A. Kluwick, S. Braun, R. Szeywerth (TU Wien) 

Steady two-dimensional laminar flows past an expansion ramp are known to exist up to a critical 

ramp angle αc in the limit as the Reynolds number tends to infinity. The theory of viscousinviscid 

interaction combined with a local bifurcation analysis is used to study the evolution of 

three-dimensional unsteady perturbations if |α − αc| ≪ 1 for both sub- and supercritical conditions. 

Special emphasis is placed on the effects of controlling devices and the phenomenon of 

bubble bursting. 

Asymptotic description of incipient separation bubble bursting 

Stefan Braun, Stefan Scheichl, Alfred Kluwick (TU Wien) 

The appearance of short laminar separation bubbles in high Reynolds number wall bounded flows 

due to appropriate adverse pressure gradient conditions is usually associated with minor effects on 

global flow properties (e.g. lift force). However, localized reverse flow regions are known to react 

very sensitively to perturbations and in further consequence may trigger the laminar-turbulent 

transition process or even cause global separation. The present investigation of marginally separated 

boundary layer flows is based on a high Reynolds number asymptotic approach. Special 

emphasis is placed on solutions of the corresponding model equations which blow up within finite 

time indicating the ejection of a vortical structure and the emergence of shorter spatio-temporal 

scales reminiscent of the early transition scenario (‘bubble bursting’). Among others, an adjoint 

operator method is used to formulate the consequential evolution equations of the viscous-inviscid 

interaction process beyond blow up. Recent analytical and numerical findings regarding this new 

stage will be presented. 

Cauchy Problems and Breakdown in the Theory of Marginally Separated Flows 

Mario Aigner, Stefan Braun (TU Wien) 

Flow separation can be viewed as one of the trigger events of laminar-turbulent boundary layer 

transition. Thus, intensive investigations have been carried out as to when and how laminar boundary 

layers break down. In the special case of marginal separation, i.e. the formation of short 

laminar separation bubbles, high Reynolds number asymptotic theory yields integro-differential 

equations governing the essential flow behavior. Since transition, which can be associated with 

”bubble bursting”, is an inherent time dependent phenomenon, initial value problems (IVPs) were 

formulated, using appropriate time scales within the according asymptotic setting. We will present 

further considerations of these problems in planar and three-dimensional flow cases regarding


the general ill-posedness, using analytical and numerical techniques to depict the spatio-temporal 

manifestation of short-scale instabilities. To regularize such disturbances, higher order asymptotic 

terms comprising the streamline curvature in the boundary layer region are taken into account. 

Evidence for well-posedness of this modified problem will be given in terms of a dispersion relation 

and numerical solutions of the full problem, especially by performing backward in time 

calculations. Even though the regularized IVPs admit limiting steady states in their time evolution, 

the phenomenon of finite time blow-up, which can be interpreted as ”bubble bursting”, is 

still present. As a consequence, the inevitable breakdown of the according flow description leads 

to the emergence of a new asymptotic structure of shorter spatio-temporal scales (yielding a so 

called nonlinear triple deck stage). Deeper insight into this next stage of the bursting process is 

still to be gained and we will conclude by presenting some first attempts in solving this problem. 

S9.3: Laminar flows and transition III Wed, 13:30–15:30 

Chair: Andreas Krumbein, Suad Jakirlic S1|01–A2 

Transition Modelling for Aerodynamic Flow Simulations with a Near-Wall Reynolds- 

Stress Model 

Axel Probst (DLR Göttingen), Ulrich Rist (Universität Stuttgart), René-Daniel Cécora, Rolf Radespiel 

(TU Braunschweig) 

Transition from laminar to turbulent flow plays a significant role in modern aircraft designs. Numerical 

simulations of flows around flying aircrafts still mostly rely on RANS (Reynolds-averaged 

Navier-Stokes) approaches which use semi-empirical closures to model turbulent flow. The most 

general level of RANS closures is achieved by modelling the six individual transport equations 

of the Reynolds-stress tensor (Reynolds-stress model, RSM). To account for near-wall turbulence 

effects additional low-Reynolds number damping functions can be applied which locally alter the 

model calibration. 

Our present approach uses the ε h -based near-wall RSM [1] in an extended formulation which 

is combined with an e N -transition-prediction method within the finite-volume flow solver DLR- 

TAU. Due to its DNS-based calibration the model is able to accurately predict the anisotropic 

Reynolds-stress and dissipation-rate profiles down to the wall. However, the damping terms were 

found to delay or even suppress transition in the low-disturbance environments of flying aircrafts. 

The simulation method is therefore extended by a novel approach to incorporate the usually neglected 

Reynolds-stress contributions by the unstable transitional modes into the RANS solution 

[2]. To derive realistic input quantities at turbulence onset a linear-stability eigenfunction analysis 

of the incoming laminar boundary layer is performed. It provides the wall-normal shapes of the 

transitional Reynolds stresses which are derived from the amplitudes and phase shifts of the most 

amplified Tollmien-Schlichting or crossflow wave at the end of linear amplification. Closure of 

the yet missing magnitudes is obtained by an additional calibration based on DNS results of an 

adverse-pressure-gradient flow. 

The talk provides a detailed overview on both the near-wall Reynolds-stress closure and the 

linear-stability-based transition model. To demonstrate the validity of the approach, computations 

of different 2D and 3D flow cases are presented, such as generic boundary layers, airfoil 

flows and a flow-through nacelle near stall. Moreover, a recent extension for combined Tollmien- 

Schlichting/crossflow transition scenarios is addressed. 

[1] Jakirlić, S., Hanjalić, K., A new approach to modelling near-wall turbulence energy and stress 

dissipation, J. Fluid Mechanics, 459 (2002), 139 – 166.


[2] Probst, A., Radespiel, R., Rist, U., Linear-Stability-Based Transition Modeling for Aerodynamic 

Flow Simulations with a Near-Wall Reynolds-Stress Model, to appear in: AIAA Journal 

(2012). 

An investigation of the separate flow and stall delay for horizontal-axis wind tubine 

Florin Frunzulica (POLITEHNICA University of Bucharest), Razvan Mahu (TENSOR SRL, 

Bucharest), Horia Dumitrescu (Institute of Mathematical Statistics and Applied Mathematics 

Bucharest) 

The flow characteristics and stall delay phenomenon of a stall regulated wind turbine rotor due to 

blade rotation in steady state non-yawed conditions are investigated. An incompressible Reynoldsaveraged 

Navier-Stokes solver is applied to carry out the separate flow cases at high wind speeds 

from 11 m/s to 25 m/s with an interval of 2 m/s. The objective of the present research effort is 

to validate a first-principles based approach for modeling horizontal-axis wind turbines (HAWT) 

under stalled flow conditions using NREL/ Phase VI rotor data. The computational results are 

compared with the predicted values derived by a new stall-delay model and blade element momentum 

(BEM) method. 

An insight into the rotational stall delay 

Horia Dumitrescu, Vladimir Cardos (Institute of Statistical Mathematics and Applied Mathematics 

Bucharest) 

Blade element and momentum methods (BEM) are the traditional design approach to calculate 

drag and lift forces of wind turbine rotor blades. The major disadvantage of these theories is 

that the airflow is reduced to axial and circumferential flow components. Disregarding radial flow 

components leads to underestimation of lift and thrus. Therefore, correction models for rotational 

effects are often used in the case of the stall controlled rotors at a constant rotation speed. At 

inboard locations, there is a strong interaction between the fast rotating flow of wake and the 3-D 

boundary layer close to the blade surface rotating with an angular velocity smaller than that of 

the fluid. This behaviour is visible from the streamlines over the blade surface during operation in 

deep stall. The knowledge extracted from the physical mechanism of 3-D rotational effects can be 

then used to develop an improved BEM model for the design of stall control-wind turbine rotor 

blades. In this study the pressure fields generated by the wake and blade are superimposed and 

the main contributions for the rise of the three-dimensional and rotational effects are described. 

Analytical and Numerical Modelling of the Safe Turn Manoeuvres of Agricultural 

Aircraft 

Bosko Rasuo (University of Belgrade) 

In this paper, a theoretical study of the turn manoeuvre of an agricultural aircraft is presented. 

The manoeuvre with changeable altitude is analyzed, together with the, effect of the load factors 

on the turn manoeuvre characteristics during the field-treating flights. The mathematical model 

used describes the procedure for the correct climb and descent turn manoeuvre. For a typical 

agricultural aircraft, the numerical results and limitations of the climb, horizontal and descending 

turn manoeuvre are given. The problem of turning flight with changeable altitude is described 

by the system of differential equations which describe the influence of the normal and tangential 

load factors on velocity, the path angle in the vertical plane and the rate of turn, as a function of 

the bank angle during turning flight. The system of differential equations of motion was solved 

on a personal computer with the Runge-Kutta-Merson numerical method. Some analytical and 

numerical results of this calculation are presented in this paper.


Ariel treating has become an integral part of modern agriculture. However, agricultural flying 

has been plagued by a great number of accidents. The manoeuvres of an agricultural aircraft 

are divided into those carried out while entering or leaving the spraying line. Despite low height 

of the aeroplane while spraying, this part of the flight is considered to be the safest because 

of an appreciable flight velocity. Upon completing a spraying run, the aircraft enters the turn 

manoeuvre procedure. 

The low altitude of the turn manoeuvre procedure and the vicinity of terrain are main causes 

of numerous accidents. The pilots assert that the procedure is the most dangerous manoeuvre 

and most of the accidents occur when these manoeuvres are performed, due to low altitude and 

the possibility of stall during the manoeuvres. There are many secondary factors that influence 

the safety of agricultural flying and some of them will be treated in this paper. 

In this paper a criterion has been established for determining the margin of the speed over the 

stalling speed (safety speed) after the agricultural aeroplane increases its height above the ground 

by a given amount. The required altitude may be different for different types of aeroplanes and 

will depend on their capability to perform rolling and turning manoeuvres. The minimum margin 

of velocity allowed is determined from the requirements of the rolling manoeuvre. 

A numerical study of vortex structures behind an harbor seal vibrissa 

Daniel Matz, Albert Baars (Bionik Innovations Centrum) 

Harbor seals (Phoca vitulina) use whiskers (vibrissa) to detect prey by their trailing wake. These 

whiskers are not circular cylinders, but show wavy elliptical structures in spanwise direction. 

This geometry is found to substantially reduce vortex shedding in the wake of the vibrissa in 

comparison to circular cylinders and elliptical structures. In this work we want to contribute to 

the question, to what extent wave length and amplitude of the shape are optimized for reduction 

of self induced oscillations. Therefore, numerical flow simulations at Re = 230 are performed to 

investigate the influence of amplitude and wavelength on vortex structures, drag and lift coefficient, 

as well as the Strouhal number. The 3D calculations are carried out with a finite volume 

code with discretization of second order in space and time. The block structured grids consists of 

around 1 · 10 7 volumes. For the basic geometry the amplitude of the lift coefficient range lower by 

a factor of 120 in comparison to a cylinder and a factor of 30 in comparison to an ellipse. This is in 

accordance with literature. The separated shear layer in the wake of the vibrissa forms complex 

3D flow pattern, which show a periodical structure in spanwise direction. For overflow length 

greater than 800 this structure gets unstable and deforms in spanwise direction. This influences 

the temporal progression of drag and lift coefficient. 

S9.4: Laminar flows and transition IV Wed, 16:00–18:00 

Chair: Martin Oberlack / Florian Kummer, Stefan Braun S1|01–A2 

A discontinuous Galerkin solver for steady incompressible flows based on the SIM- 

PLE algorithm 

Benedikt Klein, Florian Kummer (TU Darmstadt) 

For the numerical simulation of incompressible flows the finite volume method (FVM) and the 

continuous finite element method (FEM) are widely used. Besides, a newer method, the discontinuous 

Galerkin method (DGM), which has got favorable properties of both the FVM and the 

FEM, is becoming more popular. The DGM provides a convergence order of O(∆x k+1 ), where k 

is the order of the approximating polynomials. 

When simulating incompressible flows one has to deal with certain difficulties, like the nonlinearity 

in the momentum equation, a strong coupling between velocity and pressure and the lack


of an explicit equation for the pressure. The well-known SIMPLE algorithm, which was originally 

proposed by Patankar and Spalding [1], has shown to be very efficient in the context of the FVM 

and the FEM [2]. For the SIMPLE algorithm, by introducing an iterative process the discrete 

equations are linearized and decoupled. An equation for the pressure, more precisely speaking, 

for the pressure correction is derived on the discrete level. 

Using a discontinuous Galerkin discretization of the momentum and continuity equation [3], 

we present how the SIMPLE algorithm can be adapted to the DGM. Various test cases are carried 

out, which show the expected convergence rate of k + 1. 

[1] S.V. Patankar and D.B Spalding, A calculation procedure for heat, mass and momentum 

transfer in three-dimensional parabolic flows, Int. J. Heat Mass Transfer 15 (1972), 1787 – 

1806. 

[2] V. Haroutunian, M.S. Engelman and I. Hasbani, Segregated finite element algorithms for the 

numerical solution of large-scale incompressible flow problems, Int. J. Numer. Meth. Fl. 17 

(1993), 323 – 348. 

[3] K. Shahbazi, P.F. Fischer and C.R. Ethier, A high-order discontinuous Galerkin method for 

the unsteady incompressible Navier-Stokes equations, J. Comput. Phys. 222 (2007), 391 – 

407. 

Energy conserving incompressible flows on collocated and distorted grids 

Julius Reiss (TU Berlin) 

An energy preserving finite difference scheme for incompressible, constant density flows is presented. 

It is based on the idea of the skew-symmetric formulation of the non–linear transport term 

of the Navier–Stokes Equation 

∂tuα + 1 

2 (div (uuα) + u · grad (uα)) + (gradp)α = 0 

div(u) = 0 

with u = (u1, u2, u3), and α = 1, 2, 3. In contrast to established schemes collocated Euclidean grids 

can be used while exactly preserving the energy and momentum conservation, yet avoiding the 

odd–even decoupling of the Laplacian of the pressure Poisson equation. The essential idea is to use 

different discretizations for the different derivatives in the above equations. High order derivatives 

in space and time can be used. The generalization to transformed grids is discussed and full 

conservation for arbitrary transformations in two dimensions and for restricted transformations 

in three dimensions is found. 

On a reduced mixed s-v least-squares finite element formulation for the incompressible 

Navier-Stokes equations 

Alexander Schwarz, Jörg Schröder (Universität Duisburg-Essen) 

In the present work a mixed finite element based on a least-squares approach is proposed. Here, 

we consider a formulation for Newtonian fluid flow, which is described by the incompressible 

Navier-Stokes equations. First, a div-grad first-order system is derived resulting in a three-field 

approach with stresses, velocities, and pressure as unknowns. Following the idea in [1], this threefield 

formulation can be transformed into a reduced stress-velocity (s-v) two-field approach. The 

L2-norms of the residuals of the derived equations yield then the least-squares functional, which is


the basis for the associated minimization problem. Besides some numerical advantages, as e.g. an 

inherent symmetric structure of the system of equations and an error estimator, it is known that 

least-squares methods have also a drawback concerning accuracy, especially when lower-order 

elements are used, see e.g. [2,3]. Therefore, the main focus of the presentation is on performance 

and implementation aspects of triangular mixed finite elements with different interpolation order. 

In order to approximate the stresses, shape functions related to the edges are chosen. These 

vector-valued functions are used for the interpolation of the rows of the stress tensor and belong 

to a Raviart-Thomas space, which guarantees a conforming discretization of the Sobolev space 

H(div). Furthermore, standard polynomials associated to the vertices of the triangle are used for 

the continuous approximation of the velocities. The talk closes with some numerical examples, 

which focus on well-known benchmark problems for incompressible Newtonian fluid flow and 

demonstrate the performance of the mixed finite element formulation. 

[1] Z. Cai, B. Lee, P. Wang, Least-squares methods for incompressible Newtonian fluid flow: 

linear stationary problems, SIAM J. Numer. Anal. 42 (2004), 843–859. 

[2] O. Kayser-Herold, Least-squares methods for the solution of fluid-structure interaction problems, 

PhD Thesis, Technische Universität Braunschweig (2006). 

[3] A. Schwarz, J. Schröder, A mixed least-squares formulation of the Navier-Stokes equations 

for incompressible Newtonian fluid flow, Proc. Appl. Math. Mech. 11 (2011), submitted. 

Allocation of the particle concentration for the SPH-method depending on the gradients 

of flow parameters 

Anika Stein, Olaf Wünsch (Universität Kassel), Markus Rütten (DLR Göttingen), Jens Kuenemund, 

Stefan Saalfeld (Universität Göttingen) 

The Smoothed Particle Hydrodynamics method (SPH) is a Lagrangian, mesh free method to 

discretize partial differential equations like the Navier-Stokes-Equation by interpolating flow properties 

directly at a set of particles. It was first developed 1977 by [1] and [2] for astrophysical 

Problems. Today it is applied more and more for mechanical problems. It is comfortable to use 

for fluid and multiphase flow problems, large deformation problems and free surface flows because 

it is possible to allocate different properties to each particle. Moreover the differential set of the 

Momentum-Equation is particularly suitable for complex rheological problems like polymer melts, 

[3]. All the information about the flow like velocity, temperature, viscosity and so on are recorded 

at each particle for a optional number of departed time steps. It brings a lot of advantages as 

described above, but another outcome of that are costs in memory and a rising need of calculation 

power, the more particles are inside a domain. Taking in account that in some areas of a flow field 

nearly nothing happens and in some areas the gradients of flow parameters are very high, it is 

not the best choice to use the same particle concentration at those different regions. In this paper 

a method is presented to optimise this number of particles according to the gradients of the flow 

parameters. The functional principle of this operation is to generate particles at domains with 

highly alternate flow properties and to turn them out where they are not needed. This algorithm 

is able to generate more accurate solutions, which is shown by different examples like a leaked 

tank or a breaking dam. Finally the influence of the procedure is discussed. 

[1] R. A. Ginglod and J. J. Monaghan, Smoothed particle hydrodynamics theory and application 

to non-spherical stars, Mon. Not. R. Astron. Soc. 181, 375 (1977)


[2] L. B. Lucy, A numerical approach to the testing of the fission hypothesis, Astron. J. 83, 1013 

(1977) 

[3] M. Ellero, Smoothed Particle Dynamics Methods for the Simulation of Viscoelastic Fluids, 

Dissertation, Universität Berlin,(2004), urn:nbn:de:kobv:83-opus-7658 

Internal flow analysis for slow moving small droplets in contact with rough surfaces 

Raheel Rasool, Roger A. Sauer, Muhammad Osman (RWTH Aachen) 

Motivated by the self-cleaning phenomena, internal fluid flow behavior for slow moving small 

droplets in contact with rough surfaces is analyzed. The shape of the droplet is first computed 

using the Young-Laplace equation. For this purpose a Finite Element (FE) model [1], in which 

contact constraints are enforced through Penalty and Augmented Lagrange Multiplier methods, 

is used. The flow field within the droplet is then analyzed through the Stokes flow model, constituting 

a decoupled approach. Similar to the membrane deformation model, the formulation for 

the flow analysis is also expressed in the framework of FE analysis. Both, stabilized (Pressure 

Stabilizing/Petrov-Galerkin PSPG) and Galerkin FE formulations are considered. The motion 

of the fluid inside the droplet is governed by the slip condition enforced on the membrane of 

the droplet. Numerical examples for droplets rolling steadily on smooth and rough surfaces are 

presented. 

[1] M. Osman and R.A. Sauer, A two-dimensional computational droplet contact model, Proc. 

Appl. Math. Mech., 11 (2011), 103-104. 

Pattern formation and mixing in three-dimensional film flow 

Thilo Pollak, Christian Heining, Nuri Aksel (Universität Bayreuth) 

The effect of inertia on gravity-driven free surface flow over different three-dimensional periodic 

corrugations is considered analytically, numerically and experimentally. In the case of high bottom 

undulations the results predict complex free surface structures especially in cases where the 

topography is not fully flooded by the liquid film. The investigation of the flow field shows a rich 

variety of pattern formation phenomena depending on the interplay between the geometry of the 

topography and the inertia of the film. Finally, we show how the complex topographical structure 

enhances the laminar mixing within the film. 

S9.5: Laminar flows and transition V Thu, 13:30–15:30 

Chair: Ulrich Rist S1|01–A2 

Modelling study of turbulent-to-laminar transitional features of a strongly heated 

pipe flow 

S. Jakirlic (TU Darmstadt), R. Jester-Zuerker (Voith Hydro Holding GmbH Co. KG-tts, Heidenheim) 

A flow in a circular pipe subjected to increasingly enhanced wall heating is computationally investigated 

by means of a differential, near-wall second-moment closure model based on the solution 

of transport equations for second moments of the fluctuating velocities and temperature, u ′′ 

i u′′ 

j and 

u ′′ 

i 

θ respectively. Both Reynolds stress model and heat flux model represent wall-topography free 

formulations with quadratic pressure-strain term and pressure-temperature-gradient correlation.


The transport equations for the turbulent stress tensor and the turbulent heat flux are solved in 

conjunction with the equation governing a novel length-scale determining variable, the so-called 

homogeneous dissipation rate, Jakirlic and Hanjalic (2002, J. Fluid Mech., 539:139-166). Such an 

approach offers a number of important advantages: proper near-wall shape of the dissipation rate 

profile was obtained without introducing any additional term and the correct asymptotic behaviour 

of the stress dissipation components by approaching the solid wall is fulfilled automatically 

without necessity for any wall geometry-related parameter. In order to account for the influence 

of the temperature field and associated fluid property variation on the velocity field, the Favreaveraged 

equations for mass, momentum and energy are solved. The temperature dependence on 

viscosity and heat conductivity is defined via a power-law formulations, while Prandtl number 

P r and specific heat at constant pressure Cp were kept constant. Density is evaluated from the 

equation for ideal gas. 

The flow configuration considered presently, representing a vertical circular tube with air flowing 

in upward direction, was experimentally investigated by Shehata and McEligot (1998, Int. J. 

Heat and Mass Transfer, 41:4297-4313) and by means of DNS by Satake et al. (2000, Int. J. Heat 

and Fluid Flow, 21:526-534) and Bae et al. (2006, Physics of Fluids, 18(075102)). After a portion 

of a fully-developed pipe flow (length = 4D, with D being the pipe diameter) with constant wall 

temperature Θw the air enters a 30D-long pipe subjected to intensive heating (with negligible 

buoyancy effects). The thermal boundary conditions correspond to a constant heat flux. Three 

different heating rates were considered q + 

i = 0.0018, 0.0035 and 0.0045. According to the reference 

data originators, these values relate to the turbulent, sub-turbulent and laminarizing regimes. In 

the latter case some laminarization phenomena have been observed. The influence of strong heating 

of a gas flow (as, e.g., encountered in gas combustors and similar high-temperature reactors) is 

primarily manifested through a severe variation of the fluid properties (density, viscosity) leading 

consequently to important structural changes. The most important changes are concentrated in 

the immediate wall vicinity. The strongest modification of flow structure, deviating substantially 

from the equilibrium conditions, occurs in the inner part of the temperature layer. Accordingly, 

the density decrease and viscosity increase led to the thermal boundary layer growth and 

viscous sublayer thickening (relative to the boundary layer thickness reduction) causing the flow 

acceleration, which, if sufficiently strong, can suppress turbulence resulting in flow laminarization. 

The model results obtained follow closely the experimental and DNS findings manifested especially 

through the laminar-like profiles of the velocity and temperature fields. The behaviour of 

Reynolds stress components is in accordance with a severe suppression of the turbulence intensity 

due to local acceleration caused by a strong viscosity increase. 

Numerical and experimental investigations of thermal convection in an inclined narrow 

gap 

O. Sommer (TU Chemnitz), H. G. Heiland (SUVIS GmbH, Chemnitz), G. Wozniak (TU Chemnitz) 

The knowledge of the fluid behaviour in inclined cavities is of fundamental importance as far as 

heat and mass transfer are concerned. The interest in this subject is particulary increasing due 

to the rapid process in microtechnologies. We therefore studied the flow- and temperature field of 

such flows numerically as well as experimentally using CFD and PIV/ T, respectively. We present 

and discuss the numerical and experimental results of our investigations and explain the applied 

techniques. 

Gas exchange of almost leak-tight display cases 

Johannes Strecha, Herbert Steinrück (TU Wien)


A requirement for display cases for art objects is to be leak tight. However, due to design constraints 

there a are tiny gaps resulting in a gas exchange between the interior of the show case and 

its environment. Usually the leak-tightness is being quantified by the so-called air exchange rate, 

the ratio of the gas volume exchanged between display-case and environment per unit time and 

the volume of the display-case. Commonly the concentration of a tracer-gas in the display-case is 

monitored to calculate the air exchange rate. For this purpose a certain tracer-gas exchange-law is 

assumed, usually a linear exchange-law. We present experimental results that disqualify a linear 

exchange law and find that it is a special case, not applicable in general. 

We review the gas exchange mechanism through the gaps Taking hydro static pressure differences 

due to temperature and concentration differences of the tracer gas and diffusion into 

account a non linear exchange model is derived and validated experimentally. 

We conclude that in general the tracer-gas concentration has a significant influence on the gas 

exchange and therefore the assumption of a linear exchange-law is discouraged. Instead we suggest 

the introduction of two parameters: one that characterizes the air-exchange in the diffusion-driven 

limit and one that takes the influence of hydrostatic pressure into account. Strategies to identify 

these parameters will be presented and demonstrated. 

Non isothermal simulation of non-Newtonian flow in the shot sleeve of semi- solid 

die casting processes 

Roudouane Laouar, Olaf Wünsch (Universität Kassel) 

This work deals with a numerical study of the flow of metal in the semi-solid state in the shot sleeve 

of horizontal die casting machine during the injection process. With the discovery of shear thinning 

and the thixotropic behavior of partially solidified alloys under vigorous agitation, a new era in 

forming technology was started, namely semi-solid metal (SSM) processing. The new technology 

promises several important advantages in comparison with the traditional die casting processes. 

In the semi-solid state, metallic alloys consists of solid particles suspended in a liquid Newtonian 

matrix and consequently modeling approaches known from classical suspension rheology can be 

applied. In the equilibrium state, semi-solid alloys are shear-thinning and different descriptions in 

form of material equation are used in literature. In the present work, the Herschel-Bulkley model, 

which contains a yield stress and a shear-thinning viscosity, was used in order to demonstrate 

the effect of the nonlinear viscosity to the flow pattern in the shot sleeve. The used numerical 

model, which considers the problem as two-dimensional, is based on the conservation equations 

of mass and momentum, and describes the free surface using the volume-of-fluid method. The 

motion of plunger is simulated by using a layering dynamic mesh method. The numerical results 

are obtained by using a CFD code that is based in the finite volume method. The influence of 

different parameters as yield stress, the power law index and the temperature in the flow dynamics 

is to be discussed. A comparison between a Herschel-Bulkley fluid and a shear-thinning fluid with 

no yield stress limit is presented. 

Simulating of a pressing process of a viscoelastic polymer melt 

Ammar Al-Baldawi, Olaf Wünsch (Universität Kassel) 

A well known and often used method to obtain anisotropic polymer films is the so-called pressing 

process. Here, films are squeezed under high temperatures, pressure and deformation rates. To 

simulate such a process, the polymeric matrix is treated as a non-Newtonian, viscoelastic melt. 

Experimental investigations of it predict a shear thinning and elongational hardening/softening 

behavior. The modeling of this behavior is done with a generalized Maxwell Model. Where the 

generalization is obtained using a Phan-Thien and Tanner anisotropic molecule movement tensor 

for high deformation rates [1,2].


Simulating this process leads to a hyperbolic equation set of mass conservation, momentum 

balance and material model. Therefore, the simulation needs to be stabilized; here the DEVSS 

method is used. Furthermore, the ALE method is used to interpolate between the Euler and 

Lagrange description method in connection with a cell-layering method to obtain big changes in 

the calculation domain. 

In this work we present some simulations to show the difference between the classical approaches 

using a generalized Newtonian viscosity to model the polymeric matrix and the viscoelastic 

model. Here, the major difference is shown to be the pressure field and its influence on the velocity 

field and the extra stress tensor. For this end we use a flow type parameter to show the elongation 

types in the regions and the differences [1]. 

[1] A. Al-Baldawi, O. Wünsch, Some new aspects of the invariants of the rate of deformation 

tensor and their application on viscoelastic polymer melts, Accepted for publication in 

Technische Mechanik (2011) 

[2] O. Wünsch, Laminar Fluid Flow with Complex Material Behavior in Devices of Mechanical 

Engineering, Int. Journal of Emerging Multidisciplinary Fluid Sciences, 1-4, 255-267 (2009) 

S9.6: Laminar flows and transition VI Thu, 16:00–18:00 

Chair: Suad Jakirlic S1|01–A2 

Direct numerical simulation of MHD duct flow at high Reynolds number 

Dmitry Krasnov (TU Ilmenau), Oleg Zikanov (University of Michigan), Thomas Boeck (TU Ilmenau) 

Evolution of turbulent flow of an incompressible, electrically conducting fluid is studied numerically 

in a square duct subjected to a uniform magnetic field B. The magnetic field is applied in 

the vertical (wall-normal) direction, the walls are perfectly insulating. The governing equations 

are the Navier-Stokes system with the additional Lorentz force term j × B, where j is the electric 

current. There are two governing parameters, the Reynolds number Re = UqL/ν and the Hartmann 

number Ha = BL σ/ρν, which characterizes the strength of the applied magnetic field B. 

Here Uq are the mean flux velocity, L is the duct half-width and σ is the electrical conductivity. 

The Joule dissipation selectively damps out fluctuations of velocity perpendicular to the magnetic 

field that can result into anisotropy of turbulent eddies. For strong magnetic fields the 

anisotropy can evolve into 2D structures stretched along the direction of the magnetic field. Two 

major ingredients are necessary to achieve the 2D states: (i) the Reynolds number Re should 

be large, that amounts to intensive turbulent fluctuations and (ii) the interaction parameter 

N = Ha 2 /Re should exceed 1, which also means strong magnetic fields. 

In our simulations Re = 100000 and Ha = 0 ... 400. For the present study a series of DNS was 

performed at the grid resolution of 2048 × 769 × 769 points that amounts to more than 1 billion 

points as a problem size. The numerical method is based on highly conservative finite-difference 

discretization of the second order, the flow solver is hybrid-parallel (both MPI and Open MP 

interfaces). 

As Ha increases the flow transforms from nearly isotropic turbulence at Ha = 0 to a spatial 

anisotropy at Ha > 200. At Ha = 300 the core flow becomes essentially laminar, the turbulence 

remains small-scale near the side walls, but becomes large-scale, weak, and strongly anisotropic 

towards the core flow. Finally, at Ha = 400 the fluctuations die out and the flow becomes laminar. 

The quasi-2D structures have been identified in a clear-cut way by applying the so-called


lambda-2 criterion. The results of the lambda-2 visualization at Ha = 300 and 350 show a region 

with clearly expressed 2D structures stretched along the magnetic field. We have also found 

transformation of the mean velocity similar to our previous study on channel flow under spanwise 

magnetic field. This behavior is observed in the cross-section perpendicular to the magnetic field 

for a range Ha ≈ 100 ... 200. During this transformation the classical log-layer almost disappears 

and is replaced by a linear dependence. 

Visualisation of the Ludford column 

André Thess (TU Ilmenau), Oleg Andreev (Forschungszentrum Dresden-Rossendorf) 

The formation of TTaylor columnsïn rotating flows is well known: When a liquid flows over a 

truncated cylinder in a rotating systems, a stagnant region forms above the cylinder. It has been 

known for quite some time that an analogous phenomenon, the LLudford columnëxists when a 

liquid metal flows across a truncated cylinder under the influence of a magnetic field parallel 

to the axis of the cylinder. Since liquid metals are opaque, it is impossible to visualise Ludford 

columns. Using an electrolyte instead of a liquid metal and a high magnetic field created by 

a superconducting magnet we visualise for the first time the Ludford column and discuss their 

properties. We discuss further ways in which optical flow measurement can be applied to better 

understand magnetohydrodynamic flows. 

Separation of magnetic particles in channel flows by BEM 

J. Ravnik, M. Hriberek (University of Maribor), F.Vogel, P. Steinmann (Universität Erlangen- 

Nürnberg) 

In-line separation of suspensions can become difficult in in case of particles with comparable values 

of densities. For flows in micro devices in such cases gravitational settling is inefficient, and other 

separation techniques must be applied. In case of magneto active particles, the action of Kelvin 

magnetic force in a non-uniform magnetic field could be used in order to achieve a higher degree of 

particles separation. The contribution therefoe deals with Euler-Lagrangian formulation of dilute 

two-phase flows. The Boundary element based computational algorithm solves the incompressible 

Navier-Stokes equations written in velocity-vorticity formulation. The nonuniform magnetic field 

was defined analytically for the case of a set of long thin wires. The particle trajectories were 

computed by applying the 4th order Runge-Kutta method. The computed test case consisted of 

a narrow channel with laminar flow of suspension under Re=1-10. Particle trajectories under the 

influence of a nonuniform magnetic field were computed for the case of magnetite and aluminium 

particles suspended in water. The efficiency of separation on basis of particle trajectories for different 

values of Re number and magnetic field strength was performed, clearly indicating superior 

separation of magneto active particles. 

Experimental investigation of the electrokinetic flow in microchannels with internal 

electrodes 

Carsten Gizewski, Peter Ehrhard (TU Dortmund) 

In microfluidic devices, electrokinetic phenomena can be engaged to manipulate liquids, particles, 

or cells. In general, electrokinetic phenomena are related to the existence of electrical double 

layers (EDL), which are present e.g. where solid walls are in contact with electrolytes. Due to 

surface charges of the solid, ions of opposite charge are attracted and lead to a thin electrically 

non-neutral zone the EDL. The application of an electrical field, consequently, leads to forces 

onto the fluid inside the EDL, capable of driving a flow within the microchannel. This particular 

flow is termed electroosmotic. If further, the electrodes are placed inside the microchannel, due


to small distances, strong inhomogeneous electrical fields can be induced, which in turn cause 

complex flow fields. This is true despite low applied electrode potentials of a few Volts. Numerical 

simulations of various authors have shown the potential for pumping and mixing of such complex 

flows in microchannels with internal electrodes. 

We focus on the electroosmotic flow within rectangular microchannels of 100 x 200 µm cross 

section. In each microchannel eight pairs of electrodes are placed onto the top and bottom glass 

covers, whereas the offset of the electrodes is chosen differently in each of the microchannels. Due 

to the limited optical access through the glass covers, only the two velocity components which 

are tangential to the glass cover are accessible by means of the micro-particle-image velocimetry 

(µPIV). The expected electroosmotic flow, however, features vortices which cannot be recognized 

within this velocity plane. Therefore, a number of two-dimensional, two-component velocity 

fields are measured at different heights of the microchannel. From an integration of the continuity 

equation, subsequently, the third velocity component, which is normal to the glass cover, can 

be determined at reasonable accuracy. A further difficulty arises from the fact that the microparticles, 

used for µPIV, are not electrically neutral. Hence, in addition to drag forces from the 

electroosmotic flow, they experience electrophoretic forces. Hence, the particle movement appears 

to be a superposition of electroosmotic and electrophoretic effects. 

Flow characterization in a bioaffinity enrichment system for detection of relevant 

microorganisms in food 

A. Osorio Nesme, R. Benning, A. Delgado, (Universität Erlangen-Nürnberg) 

In food industry the quality assurance and consumer protection represent essential requirements 

for preserving high product ratings and competitiveness. Decreases in food quality or risks to 

consumers health must be properly detected in time to avoid image damage to the companies 

or risks from the product liability. In particular, the detection of microorganisms is of great 

importance. In general, this can be carried out by the routine microbiological diagnostic, whose 

negative results can be obtained only after 24 (Staphylococcus aureus) or 48 hours (Bacillus 

cereus). Furthermore, the confirmation of positive samples can take up to 144 hours. From the 

perspective of the current state of art, this analysis time could be for the microorganisms S. 

aureus and B. cereus significantly reduced by means of the development and combination of new 

analytical techniques. In the present study, a new system for direct detection of S. aureus and 

B. cereus (spores) through bioaffinity enrichment is introduced by means of a fully automated 

selective-microarray device (microporous columns) for milk and whey. The system consists of 

a monolithic column with a microporous structure, in which biological receptors (monoclonal 

antibodies or aptamers) are immobilized on the surface. These receptors have a specific interaction 

with the microorganisms (bioaffinity). The matrix (milk) flows through the monolithic column, 

allowing the microorganisms to come in contact with the receptors and get bound to the column 

surface. It has been found that the amount of microorganisms captured during the process depends 

not only on the binding kinetics but also on the flow characteristics. High flow rates signify 

less residence time of the microorganism in the column and therefore less probability of getting 

captured. The flow velocity and flow distribution along the column have a direct impact on the 

binding process (microorganism enrichment). An important part of the present work consists of 

the optimization of the column geometry by means of numerical simulations. The influence of the 

inlet form of the monolithic column on both flow and pressure distribution is investigated.

Section 9: Laminar flows and transition - GAMM 2012

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?