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SIEMENS, MUELHEIM 1 1 Fluid-Structure Interaction for Combustion Systems Artur Pozarlik Jim Kok FLUISTCOM SIEMENS, MUELHEIM, 14 JUNE 2006

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SIEMENS, MUELHEIM 2 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

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SIEMENS, MUELHEIM 3 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

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SIEMENS, MUELHEIM 4 4 Flexible liner Shape Rectangular (50 x 150 mm) Square (150 x 150 mm) Thickness4.0 mm Flexible part thickness 1.2; 1.0; 0.8 mm Flexible section length 200; 400; 600; 680 mm Investigated temperature Cold case 25 O C Hot case 760 O C Investigated models Structural Structural with combustion chamber Structural with combustion chamber and cooling passage MaterialStainless 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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SIEMENS, MUELHEIM 5 5 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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SIEMENS, MUELHEIM 6 6 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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SIEMENS, MUELHEIM 7 7 One way interaction Abs. pressure1.5 bar Air factor1.8 Total mass flow rate 90.64 g/s Number of elements 632 000; mostly in fire zone Shape Quarter section with periodic boundaries Turbulent model k- Combustion model Eddy Dissipation and Finite Rate Chemistry Initial conditions Initial velocity and turbulences are taken from previous full model calculation Pulsation 5% pulsation of equivalence ratio with frequency 100 Hz Fig. 7. Data for CFX reacting calculationFig. 8. Velocity and temperature profiles

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SIEMENS, MUELHEIM 8 8 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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SIEMENS, MUELHEIM 9 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 coefficients, which determinate damping matrix [C] as: [C]= , where [M] and [K] are mass matrix and stiffness matrix, respectively

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SIEMENS, MUELHEIM 10 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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SIEMENS, MUELHEIM 11 One – way interaction Fig. 11. Deformation shapes obtained during one-way analysis (case dynamic analysis in Ansys)

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SIEMENS, MUELHEIM 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. Master (Ansys) created socket Slave (CFX) connect to master Get code info Serve global control info Serve code info Get global control info Get interface meshes Do mapping Get initial load and restart loads Serve interface meshes Serve initial and restart loads Serve time step begin and stagger begin Get Load transfer Do solve Load transfer Do solve Load transfer Get slave local convergence Serve global convergence Serve time convergence Serve local convergence Get global convergence Get 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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SIEMENS, MUELHEIM 13 Two – way interaction Fig. 12. Deformation pattern Fig. 13. Temperature profileFig. 14. Pressure distribution

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SIEMENS, MUELHEIM 14 Two – way interaction Fig. 15. Pressure distributions along centerlineFig. 16. Max and min pressure at the flexible liner Fig. 17. Pressure distributions at midpoint near wallFig. 18. Liner displacement profile at midpoint

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SIEMENS, MUELHEIM 15 Backward Facing Step Where: H 1 – upstream channel H – step X r – reattachment length u/u 0 y/H x/H=4 x/H=6 x/H=10 x/H Cf*1000 Legend: O Jovic data □ SST x k- Fig. 19. Flow over backward facing stepFig. 21. Skin friction distribution over bottom wall Fig. 20. Axial velocity profiles x y

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SIEMENS, MUELHEIM 16 Backward Facing Step with heat transfer q Fig. 22. Flow over BFS with heat transferFig. 23. Skin friction coefficient over bottom wall Fig. 24. Temperature profilesFig. 25. Stanton number profiles x y

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SIEMENS, MUELHEIM 17 Backward Facing Step with heat transfer q u Pulsation: 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 coefficientFig. 28. Mean Stanton number x y

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SIEMENS, MUELHEIM 18 Backward Facing Step with heat transfer a) 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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SIEMENS, MUELHEIM 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

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SIEMENS, MUELHEIM 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

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