Post on 15-Jan-2016
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SIEMENS, MUELHEIM
Fluid-Structure Interaction for Combustion Systems
Artur PozarlikJim Kok
FLUISTCOMSIEMENS, MUELHEIM, 14 JUNE 2006
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Work performed
Numerical investigation of a cold flow within plenum and combustor chamber and reacting
flow within combustion chamber with the use of commercial CFX code
Reacting flow calculations by using computational code developed at the University of
Twente (CFI)
Design more flexible liner for better fluid-structure interaction (structural Ansys code)
One-way fluid-structure interaction from fluid to structure with the use of CFX and Ansys
(static and dynamic analysis)
Two-way fluid-structure interaction
Backward Facing Step with heat transfer
Participations in DESIRE fire experiment
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Flexible liner
The most dangerous frequencies occur in real gas turbines are below 500 Hz
Present test rig has first eigenfrequency around 200 Hz and low vibration amplitude
To improve response walls on changes in pressure field inside combustion chamber new model of liner with first eigenfrequency below 100 Hz and elevated vibration amplitude was design
To obtain prescribed eigenfrequency
several models of liner with different
in shape, thickness, length of flexible
section was investigated
Fig. 1. Liner configuration
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Flexible liner
ShapeRectangular (50 x 150 mm)
Square (150 x 150 mm)
Thickness 4.0 mm
Flexible part thickness
1.2; 1.0; 0.8 mm
Flexible section length
200; 400; 600; 680 mm
Investigated temperature
Cold case 25 OC
Hot case 760 OC
Investigated models
Structural
Structural with combustion chamber
Structural with combustion chamber and cooling passage
Material Stainless steal 310
Element types
Fluid – Fluid 30
Fluid-Structure – Fluid 30
Solid – Shell 63
Fig. 2. Different shapes of investigated liner
Fig. 3. Model of the numerical connection between structure and cavities
Fluid
Fluid – Structure
Structure
Connection between structural parts
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Flexible liner
Fig. 4. Eigenfrequencies [Hz] in case of a different a) shape, b) length, c) thickness, d) surrounding cavities, e) temperature
Fig. 5. Mode shapes in case of a square cross-section, 0.8mm thickness and 680mm length liner in high temperature, without air cavities
a) b) c) d)
e)
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One – way interaction
Fig.6. Implementing results from CFX to Ansys
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.
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One way interactionAbs. pressure 1.5 bar
Air factor 1.8
Total mass flow rate
90.64 g/s
Number of elements
632 000; mostly in fire zone
ShapeQuarter section with periodic boundaries
Turbulent model k-Combustion model
Eddy Dissipation and Finite Rate Chemistry
Initial conditionsInitial velocity and turbulences are taken from previous full model calculation
Pulsation5% pulsation of equivalence ratio with frequency 100 Hz
Fig. 7. Data for CFX reacting calculation Fig. 8. Velocity and temperature profiles
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One – way interaction
Fig. 9. Liner boundary conditions 7 500 equally distributed elements
One wall taken into account
Simplified geometry (without holes, modular parts together, etc)
Wall treated as clamped on each side
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Damping mechanisms
Frictional damping
Damping of vibration energy in metallic structure itself
Damping by induced flow/acoustic radiation by the liner
Ansys – calculation done with coefficients, which determinate damping matrix [C] as:
[C]= ,
where [M] and [K] are mass matrix and stiffness matrix, respectively
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One – way interaction
Fig. 10. Numerical results of the total deformation and the reduced stress pattern in the case of static analysis in structural code
Numerical calculations was done for two different cases:
transient calculations in CFX and static in Ansys – pressure field exported from CFX to Ansys transient calculations in CFX and dynamic in Ansys – pressure field exported from CFX to Ansys
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One – way interaction
Fig. 11. Deformation shapes obtained during one-way analysis (case dynamic analysis in Ansys)
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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
Slave (CFX) connect to master
Get code infoServe global control info
Serve code infoGet global control info
Get interface meshesDo mapping
Get initial load and restart loads
Serve interface meshesServe initial and restart loads
Serve time step begin and stagger begin
Get
Load transfer Do solve
Load transfer
Load transferDo solve
Load transfer
Get slave local convergenceServe global convergenceServe time convergence
Serve local convergenceGet global convergenceGet time convergence
Numerical codes used:
Ansys 10
Ansys CFX 10
MFX Ansys
All boundary conditions in CFX and Ansys the some as during one – way interaction
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Two – way interaction
Fig. 12. Deformation pattern
Fig. 13. Temperature profile Fig. 14. Pressure distribution
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Two – way interaction
Fig. 15. Pressure distributions along centerline Fig. 16. Max and min pressure at the flexible liner
Fig. 17. Pressure distributions at midpoint near wall Fig. 18. Liner displacement profile at midpoint
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Backward Facing StepWhere:H1 – upstream channel H – step Xr – reattachment length
u/u0
y/H
x/H=4 x/H=6 x/H=10
x/H
Cf*
100
0
Legend:O Jovic data□ SSTx k-
Fig. 19. Flow over backward facing step Fig. 21. Skin friction distribution over bottom wallFig. 20. Axial velocity profiles
x
y
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Backward Facing Step with heat transfer
q
Fig. 22. Flow over BFS with heat transfer Fig. 23. Skin friction coefficient over bottom wall
Fig. 24. Temperature profiles Fig. 25. Stanton number profiles
x
y
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Backward Facing Step with heat transfer
q
uPulsation: sin amplitude 0.2 frequency 10, 100,400, 1000 Hz SST
Fig. 26. Pulsating flow over BFS with heat transfer
Fig. 27. Mean skin friction coefficient Fig. 28. Mean Stanton number
x
y
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Backward Facing Step with heat transfera) b)
c) d)
Fig.29. Axial velocity profiles in case of perturbation with frequency: a) 10 Hz, b) 100 Hz, c) 400 Hz, d) 1000 Hz
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Conclusions The shape, temperature, and the liner flexible section thickness and length have a major influence
on the walls eigenfrequency, minor influence air cavities was observed
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
One-way interaction gives only insight into real system behavior when both analyses are transient.
Two-way interaction shows significant distribution in pressure pattern as a case of vibrating walls
Both, one- and two-way interactions, predicted similar wall deformation and stress
BFS with heat transfer is matched well with experimental results, especially SST turbulence model.
Significant influence of pulsation frequency on flow pattern was noticed
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Future work
Further numerical investigation of one – way interaction from vibrating wall to fluid inside combustion chamber
Flame transfer function analysis
Experimental work at test rig