Fluid-Structure Interaction for Combustion Systems - cerfacs

FLUISTCOM
UNIVERSITY OF TWENTE, ENSCHEDE, 18 JANUARY 2006
Fluid-Structure Interaction
for Combustion Systems
Artur Pozarlik
Jim Kok
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UNIVERSITY OF TWENTE, ENSCHEDE

Work performed
• Start: October 2004
• Numerical investigation (CFX) of a cold flow within plenum and combustor
chamber; reacting flow within combustion chamber (burner mouth velocity profile,
species concentration, temperature profile)
• Reacting flow calculations by using computational model developed at the
University of Twente (CFI)
• Design more flexible liner for better structure – fluid interaction by using ANSYS
Code (influence of shape, length, and liner flexible section thickness on walls
stiffness)
• One – way fluid – structure interaction (forces field) by using commercial codes
CFX and Ansys
• First steep into two – way fluid – structure interaction (forces field) by using MFX
Ansys
• Participations in DESIRE fire experiment
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UNIVERSITY OF TWENTE, ENSCHEDE

Test rig development
• Systematic investigation of interaction of fluid to structure and vv
• Present test rig: liner vibrations at very low amplitude
• First eigenfrequency high: 200 Hz
• Improved test rig elevated vibration amplitude
• First eigenfrequency below 100 Hz
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UNIVERSITY OF TWENTE, ENSCHEDE

Flexible liner designing
Shape
Thickness
Flexible part thickness
Flexible section length
Investigated
temperature
Investigated models
Material
Rectangular (50 x 150 mm)
Square (150 x 150 mm)
4.0 mm
1.2; 1.0; 0.8 mm
200; 400; 600; 680 mm
Cold case 25 O C
Hot case 760 O C
Structural
Structural with combustion
chamber
Structural with combustion
chamber and cooling passage
Stainless steal 310
Fig. 1. Liner configuration
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UNIVERSITY OF TWENTE, ENSCHEDE

Eigenfrequencies investigation
Fig.2. Eigenfrequencies [Hz] of the
rectangular and square crosssection
liner with the some flexible
part dimensions (0.8 mm thickness
and 680 mm length)
Fig.3. Eigenfrequencies [Hz] of the
square cross-section flexible liner
part and whole liner structure for the
flexible section lengths 400 and 680
mm
Fig.4. Fluid-structural cold and
hot calculations of the
eigenfrequencies for the liner thin
section length 400 mm and
thickness 0.8 mm
The most flexible liner seems to be square one with dimensions of 5 flexible section 680 mm
length and 0.8 mm thickness
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UNIVERSITY OF TWENTE, ENSCHEDE

Temperature and pressure
dependence investigation
Fig.5. Stress and deformation pattern in case of thermal and mechanical loads
Temperature 760 O C, base fixed in Z direction
Pressure 5000 Pa, basis fixed in all directions
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UNIVERSITY OF TWENTE, ENSCHEDE

Thermoacoustics modeling
• For thermoacoustics and vibration modeling efforts on:
• Turbulent fluid flow
• Combustion
• Induced pressure field
• Structural vibrations
• Acoustics induced by vibrations
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UNIVERSITY OF TWENTE, ENSCHEDE

Reacting flow in CFX and CFI
Abs. pressure
Air factor
Total mass flow rate
Number of elements
Shape
Turbulent model
Combustion model
1.5 bar
1.8
90.64 g/s
632 000; mostly in fire zone
Quarter section with periodic
boundaries
k-ε
•CFX - Eddy Dissipation and
Finite Rate Chemistry
•CFI (reaction progress
variable)
Initial conditions
Initial velocity and turbulences
are taken from previous full
model calculation
Fig. 6. Combustion chamber mesh distribution
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UNIVERSITY OF TWENTE, ENSCHEDE

Comparison CFX and CFI results
CFX
Fig. 7. Reacting flow models:
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CFI
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UNIVERSITY OF TWENTE, ENSCHEDE

One – way interaction, boundary conditions
Fig. 9. Liner
boundary
conditions and
pressure
distribution
CFX -
transient
Ansys
The some model as during steady – state reacting flow calculations with
exception to 5% perturbation of the equivalence ratio
Model consist of 7 500 equally distributed elements
Only one wall is taken into consideration
The liner geometry is simplified (two modular parts are treated as one, no
holes for thermocouple holes, no connection between liner modular parts etc.)
All degrees of freedom from the sides parts of the liner are taken away
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UNIVERSITY OF TWENTE, ENSCHEDE

One – way interaction
One – way interaction is a sequential process of the fluid and the solid physics coupling.
The surface pressure and the shear from the flow in the combustion chamber were computed
by using CFX CFD simulation. The normal and tangential components of mechanical load are
later transferred to the mechanical analysis in the Ansys code. The stress and deformation of
the flexible walls are predicted.
Fig.8. Implementing results from CFX to Ansys
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UNIVERSITY OF TWENTE, ENSCHEDE

One – way interaction, pressure results
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Fig. 10. Numerical
calculations of the total
deformation and the
reduced stress pattern with
the case of 690 [Pa] (left
figures) and 870 [Pa] (right
figures) pressure
difference
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UNIVERSITY OF TWENTE, ENSCHEDE

Two – way interaction
• Numerical codes used:
• Ansys 10
• Ansys CFX 10
• MFX Ansys
• University of Twente input: coding of user interfaces
• Setting of boundary conditions
• Improvement of pressure field calculations
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UNIVERSITY OF TWENTE, ENSCHEDE

Two – way interaction
Two – way interaction is a sequential or simultaneously combined of the fluid and solid physics
analysis. In opposite to one – way interaction both codes: Ansys and CFX serve and receive
information from numerical calculation.
Master (Ansys) created
socket
Get code info
Serve global control info
Get interface meshes
Do mapping
Get initial load and restart
loads
Serve time step begin and
stagger begin
Load transfer
Do solve
Load transfer
Get slave local convergence
Serve global convergence
Serve time convergence
Slave (CFX) connect to
master
Serve code info
Get global control info
Serve interface meshes
Serve initial and restart loads
Get
Load transfer
Do solve
Load transfer
Serve local convergence
Get global convergence
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Get time convergence
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UNIVERSITY OF TWENTE, ENSCHEDE

Two – way interaction, results
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UNIVERSITY OF TWENTE, ENSCHEDE

Conclusions
• The shape, temperature, and the liner flexible section thickness have a major
influence on the walls eigenfrequency. The length of flexible part is only
important in the case of small dimensions, after passing some boarder
dimension have not any influence anymore. Minor influence of the combustion
chamber and cooling passage on the structural modes were noticed. Model of
the liner with 680 mm length and 0,8 mm thickness appears to be the
appropriate one for cases of the FLUISTCOM Project
• Both CFI and the standard CFX model capture the some axial velocity profile
with two recirculation zones which provide a flame stabilization, but some
differences in the flame length and shape were obtained during calculations
• The temperature has only significant influence on the axial liner deformation.
Thermal stresses are very small as a case of the liner modular building
• The pressure pattern obtained during one – way interaction analysis shows
small deformations in the liner structure (about tenth part of mm)
• Two – way interaction more liner modes are observed, 16 also significant fluid
pressure and combustion oscillations are predicted
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UNIVERSITY OF TWENTE, ENSCHEDE

Future work
• Further numerical investigation of one – and two – way interaction
• Heat transfer and combustion calculations during DLR visit
• Flame transfer function analysis by Linear Coefficient Method
• Experimental work at test rig
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UNIVERSITY OF TWENTE, ENSCHEDE