Flui d- St ructure Interaction for Com bustion Systems Artur Pozarlik Jim Kok

1. FLUISTCOM SIEMENS, MUELHEIM, 14JUNE 2006 Fluid-Structure Interaction for Combustion SystemsArtur PozarlikJim Kok 1

2. 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 2

3. 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 3

4. Flexible liner Fig. 2. Different shapes of investigated liner Fluid Fluid – Structure Structure Connection between structural parts Fig. 3. Model of the numerical connection between structure and cavities 4

5. Flexible liner c) d) a) b) Fig. 4. Eigenfrequencies [Hz] in case of a different a) shape, b) length, c) thickness, d) surrounding cavities, e) temperature e) Fig. 5. Mode shapes in case of a square cross-section, 0.8mm thickness and 680mm length liner in high temperature, without air cavities 5

6. 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.6. Implementing results from CFX to Ansys 6

7. One way interaction Fig. 7. Data for CFX reacting calculation Fig. 8. Velocity and temperature profiles 7

8. One – way interaction • 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 Fig. 9. Liner boundary conditions 8

9. 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 a, b coefficients, which determinate damping matrix [C] as: [C]= a[M] + b[K], where [M] and [K] are mass matrix and stiffness matrix, respectively 9

10. One – way interaction • 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 10

11. One – way interaction 11

12. 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. All boundary conditions in CFX and Ansys the some as during one – way interaction • Numerical codes used: • Ansys 10 • Ansys CFX 10 • MFX Ansys 12

13. Two – way interaction 13

14. Two – way interaction 14

15. Backward Facing Step Where: • H1 – upstream channel • H – step • Xr – reattachment length y x x/H=10 x/H=6 x/H=4 Cf*1000 y/H Legend: O Jovic data □ SST x k-e u/u0 x/H 15

16. Backward Facing Step with heat transfer y x q 16

17. Backward Facing Step with heat transfer • Pulsation: • sin • amplitude 0.2 • frequency 10, 100,400, 1000 Hz • SST u y x q 17

18. Backward Facing Step with heat transfer b) a) d) c) 18

19. 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 19

20. 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 20