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02 AERODYNAMICS
reduced frequency have been set to match one of the reduced
frequencies of the aforementioned experiment, while the Mach
number has been increased from the experiment’s Mach number
0.12 to 0.4 to reduce computational time. The data set includes field
solutions from Euler as well as from Reynolds averaged Navier-
Stokes (RANS) calculations for four equidistant instants within one
oscillation cycle and for the corresponding static solution (alpha = 9
deg). Comparison of the Euler and RANS solutions shows the well
known differences in strength and spanwise location of the primary
vortex-induced suction peak due to the absence of a secondary
vortex in the Euler solution. The agreement with the experimental
results is very good.
Author
Euler Equations Of Motion; Navier-Stokes Equation; Delta Wings;
Mathematical Models; Numerical Analysis; Oscillating Flow; Vortex
Breakdown
20010009862 British Aerospace Defence Ltd., Military Aircraft and
Aerostructures, Brough, UK
M219 CAVITY CASE
Henshaw, M. J. de, British Aerospace Defence Ltd., UK; Verification
and Validation Data for Computational Unsteady Aerodynamics;
October 2000, pp. 453-472; In English; See also 20010009839;
Copyright Waived; Avail: CASI; A02, Hardcopy
The data contained in this set consists of pressure time
histories measured on the ceiling of an empty rectangular cavity, and
were measured as part of a joint BAe./DERA programme at the ARA
wind tunnel at Bedford during November 1991. The overall programme
consisted of several configurations, with bodies positioned
at various proximities to the cavity, but the data presented here only
considers the empty cavity, configured for both shallow and deep
cases. Data were measured using Kulite transducers along the
centreline of the rig, (which did not coincide with the centreline of the
cavity itself), and, in an alternative configuration, on the centreline of
the cavity. Measurements taken off the cavity centreline, but not
included here, indicated that 3D effects were not significant.
Author
Cavities; Data Acquisition; Pressure Measurement
20010009863 Deutsche Forschungsanstalt fuer Luft- und
Raumfahrt, Inst. of Design Aerodynamics, Brunswick, Germany
DLR CAVITY PRESSURE OSCILLATIONS, EXPERIMENTAL
Delfs, Jan, Deutsche Forschungsanstalt fuer Luft- und Raumfahrt,
Germany; Verification and Validation Data for Computational Unsteady
Aerodynamics; October 2000, pp. 481-487; In English; See
also 20010009839; Copyright Waived; Avail: CASI; A02, Hardcopy
Windtunnel tests were carried out with the aim of establishing a
measured unsteady surface pressure data set in and around a boxshaped
shallow cavity, subject to tangential flow in the transonic
Mach number range. Apart from the baseline case, for which
systematic Mach number and Reynolds number variations were
completed, the main purpose of the tests was to investigate the
effect of certain upstream mounted passive flow control devices on
the cavity oscillations for selected Mach numbers. This chapter
contains the description of two baseline case data sets of unsteady
surface pressures for freestream Mach number M_ = 0.8 and M_ =
1.33 respectively, made available to RTO. The main purpose of the
experiment was to test techniques for the passive control of pressure
oscillations occurring in and near cavities exposed to tangential
transonic flows. Moreover, the phase relation among the different
cavity modes were investigated since the design of devices (passive
and especially active) for control, critically depends on the knowledge
and an understanding of the underlying physical mechanisms
responsible for the resonances driving the phenomenon. Despite its
long term investigation and the corresponding vast literature on
cavity oscillations, reliable prediction schemes exist only for the
frequencies of the oscillation modes. An insight into the phase
relations among the modes however is necessary e.g. in order to lay
out the characteristics of a controller for a closed loop active control
of the oscillations. Therefore the present tests were also performed
to reveal the spatio- temporal phase relation among the modes in the
cavity. The tests were done in the DLR wind tunnel TWG (Transonic
Windtunnel Gottingen) in November 1997. The closed system tunnel
has a test section area of 1m x 1m and is operated continuously. The
cavity oscillation model is mounted on a cropped sting and consists
basically of a flat plate, containing the cutout for the box-shaped
cavity of length L = 0.202 m, width W = 0.03 m and depth D = 0.05
10
m, which in turn is hosted in the fuselage carrying the model.
Unsteady surface pressures were measured using flush mounted
Kulite pressure transducers as specified. The static pressures at
three positions on the plate surface upstream of the cavity were
measured in order to determine the actual Mach number of the flow
above the cavity. A geometrical angle of attack of alpha = 1 deg was
set in order to assure non-separating flow at the sharp leading edge
of the plate. The cavity’s bottom surface was made of an aluminium
plate, which could be translated along the x-direction (streamwise)
with the help of a remote-controlled electric motor. Six equally (in chi)
spaced Kulite sensors were flush mounted into the moveable plate.
It was possible to take measurements at arbitrary chi-positions of the
cavity’s bottom surface by moving the plate (and thus the six
sensors) to the desired setting. For each flow parameter this was
done for 12 positions of the plate. From one position to the next, the
plate was advanced upstream in steps of 3 mm. For each of these
settings the time histories of all Kulite sensors (including all nonmoveable
sensors) were recorded simultaneously along with the
static flow data. Thus for each of the 12 positions the phase relation
between all sensors can be evaluated.
Author
Experimentation; Active Control; Transonic Speed; Remote Control;
Pressure Oscillations; Wind Tunnel Tests; Cavity Flow
20010009864 Glasgow Univ., UK
DYNAMIC STALL DATA FOR 2-D AND 3-D TEST CASES
Galbraith, R. A. McD, Glasgow Univ., UK; Coton, F. N., Glasgow
Univ., UK; Green, R. B., Glasgow Univ., UK; Vezza, M., Glasgow
Univ., UK; Verification and Validation Data for Computational Unsteady
Aerodynamics; October 2000, pp. 489-533; In English; See
also 20010009839; Sponsored in part by the EPSRC; Copyright
Waived; Avail: CASI; A03, Hardcopy
Although substantial work has been carried out and much
understanding gained of the phenomena associated with dynamic
stall, our description and understanding of it is incomplete. Even if we
consider the nominally two-dimensional flow associated with most
experiments, some significant anomalies have yet to be explained.
Fully three-dimensional experiments are few and, as might have
been expected, raise more questions than have been answered. The
purpose of the selected cases herein is to provide the computational
fluid dynamic specialists with a variety of test data to assess the
output of their codes. The experimentalists may then obtain additional
information from the CFD specialists so that together the
knowledge and understanding of dynamic stall and the associated
anomalies may be enhanced. As described by Young, the nominally
two-dimensional case is considered to be characterized by a dynamic
overshoot of the aerodynamic coefficients followed by stall
onset and the roll-up of the shed vorticity into a coherent vortex that
convects over the upper surface of the aerofoil and then off into the
mainstream. It is the convection speed of the main vortex (dynamic
stall vortex) in which a distinctive anomaly has been identified by
Green et al. It was observed that certain data indicated an independence
of the convection speed from the motion of the model, whilst
others did not. Of all the influencing factors that could have contributed
to that clear difference of result, such as aerofoil shape, aspect
ratio, surface finish, data reduction software and Mach number, all
but the Mach number had no effect on the observed trends. Green
and Galbraith concluded that the most likely contender causing the
two very different results would be the difference in the Mach number
between the experimental set-ups. Albeit the data sets contained in
section 1 are for low Mach numbers (M = 0.12) they do cover a wide
range of reduced pitch rate. If CFD results reproduce the constancy
of ‘stall vortex’ convection speed observed, then it would be helpful
to recalculate for a few higher Mach numbers; say, 0.2, 0.4 and 0.7.
Although the Glasgow data (covering 14 different models) indicated
an independence of convection speed with regard to the reduced
pitch rate and the reduced frequency, there was a variation between
different models. It was observed, however, that the speed did
appear to be dependent on the shape of the aerofoil and the method
of transition. It appeared that, if a transition strip was placed at the
leading edge (consisting of filtered grit) then the convection speed
was reduced and, similarly, the scatter. Suitably ‘tripped’ data are
contained in section 2. Section 2 presents data from two NACA 00 15
aerofoils of different aspect ratio. It is hoped that the spread of test
cases can be used to assess the quality of prediction of low-speed
dynamic stall. The data are for motions of ‘ramp-up’, ‘ramp-down’
and oscillatory pitch. Both the ramp-up and ramp-down are important