Arnab Banerjee Mechanical Engineering IUPUI MSME Thesis Presentation Advisor: Prof. Razi Nalim

1. Prediction And Design Of Fuel-Air Mixing in a Combustion Wave Rotor Using Two-Dimensional Unsteady Moving Mesh Flow Computation Arnab Banerjee Mechanical Engineering IUPUI MSME Thesis Presentation Advisor: Prof. Razi Nalim November 27, 2005

2. Develop a methodology to study multidimensional effects of wave rotors and apply to NASA four-port pressure exchanger using commercial CFD code Predict the fuel-air mixing in an internal combustion wave rotor (ICWR) Determine key parameters that affect the fuel-air distribution in a wave rotor and improve understanding to obtain desired fuel distribution Objectives of the present work

3. Wave Rotor: A device for energy exchange efficiently within fluids of differing densities by utilizing unsteady wave motion Two configurations studied here NASA four-port pressure exchanger Internal combustion wave rotor (ICWR) Introduction

4. Turbine inlet pressure is 15% -20% more than compressor exit pressure ideally Increased overall engine thermal efficiency and specific work NASA four-port pressure exchanger Inlet from the Burner Exits to Turbine and Burner Inlet from the compressor Partially cut away 3D view Schematic of a gas turbine topped by a four-port wave rotor

5. Internal Combustion Wave Rotor (ICWR) Wave Rotor Compressor Turbine Schematic of ICWR • Constant Volume Combustion

6. 2D & 3D view of wave rotor

7. Developed in-house by Khalid (2004-05) Hexagonal unstructured grid Parametric geometry and grid Grid and geometry stored in small portable files Variable port/rotor channel counts and shape Tailored grid clustering Imports and exports STAR-CD files 3D and “unwrapped” simultaneous view Runs easily on laptops (windows) Pre- and Post- Processing Package

8. Results of two grid packages IUPUI in-house code Star-Design

9. Past 1-D simulations Paxson and Nalim 1-D code (1997) Berrak and Nalim Detonation 1-D code (2004)

10. Past 2-D simulations Piechna et.al (2004) wave rotor Welch (1997) NASA 4-port Kerem & Nalim (2002) single channel

11. Arbitrary Sliding Interface MARS (Monotone Advection Reconstruction Scheme) – 2nd order accurate PISO predictor-corrector algorithm Corrector stages below specified limit (20) indicates convergence reached for specified residual tolerance Solution Methodology

12. Arbitrary Sliding Interface

13. Use shock tube with different grid resolutions representing the range of CFD simulations carried out Calculated artificial diffusion from known equation Compared these values with physical diffusivity in simulations Estimating Artificial Diffusivity

14. Shock tube Ti Physical Diffusivities: Thermal diffusivity for air ~0.00002 Turbulent diffusivity for ICWR case ~0.5 Distance along tube

15. AVIDD Linux Cluster Huge Scratch space Batch Scheduling Accessible from outside of network (SSH) Dual CPU PC Quick turnaround Debugging Manual decomposition 15 Hardware Resources

16. Welch (1997) simulated NASA 4-port configuration using code validated against experiment 2D unsteady, laminar, compressible, ideal gas, adiabatic walls, no leakage IUPUI simulation Same as above and also included passage to passage leakage Methodology Development

17. Grid Resolution

18. Grid discretization comparable to Welch (1997)

19. Computed instantaneous total temperature 400 1200 IUPUI Welch-2D

20. Interface skewing between cold driven flow and hot driver flow not seen in one-dimensional computations Hot driver gas coats the trailing end of the high pressure exit port thus discharging more hot gas to the burner

21. Computed instantaneous static temperature contours showing close up view of passage gradual opening process and 2D flow features IUPUI Welch-2D

22. Include multidimensional effects Include turbulence modeling (k-epsilon with wall functions) Include species transport equations Include property dependence on mixture composition and temperature Examine the effect of fuel-air distribution on combustion Fuel-Air Mixing in an Internal Combustion Wave Rotor (ICWR)

23. Boundary Conditions - from Alparslan, Nalim and Synder (2004) • Inlet was specified as total conditions • Total pressure at inlet segments  109 KPa • Total temperature at inlet segments  291 K • Exit port was specified as static conditions • Static pressure at  72 KPa • Hot gas injection port • Static temperature  600 K • Combustion using one-step reaction combined time scale model C3H8 + 5O2  3CO2 + 4H2O • the reaction time scale is the sum of the dissipation and chemical kinetics time scales.

24. ICWR geometry

25. Grid Resolution Ignition port

26. Inlet species compositions Species Mass Fractions Air Inlet Fuel-air Inlet Fuel or Air Inlet Direction of Flow

27. Non-Combustion Pressure waves for time converged solution 10.5 KPa 182.6 KPa

28. Fuel distribution for one-dimensional and two-dimensional Red indicates stoichiometric fuel-air mixture, the desired fuel fraction for the ignition region

29. Fuel-air interface at the middle of the inlet has expected skew (tangential non-uniformity) due to passage opening to fuel over time Fuel-air interface forming at the beginning of the inlet is less skew The skew of interface maybe something useful to control Shape of fuel-air interface

30. Close-up view of first inlet segment opening to rotor passage“tufts indicate flow vectors relative to rotor” Vabs Vrel General velocity diagram Vabs Vrel Modified relative velocity diagram for present case

31. All the inlet port segments have the same total pressures First inlet segment has higher static pressure than other segments due to higher pressure from rotor passage Thus absolute velocity in the first inlet segment is lower than other segments Non-axial relative velocity forces more fuel into the trailing side of the passage Developing more uniform fuel-air interface

32. Reduced total pressure at first inlet segment

33. Increased total pressure at first inlet segment

34. Decreasing total pressure at first inlet segment has backflow  not helping in the fuel distribution shape in other passages The fuel-air interface is skewed similar to fuel air interaction in middle of inlet ports Increasing total pressure at first inlet segment causes no backflow The fuel-air interface is skewed too Results of varying total pressure at first inlet segment

35. Adding air-buffer as first inlet segment

36. The non-axial relative velocity in the first inlet segment which doesn’t have fuel  doesn’t influence the filling of fuel in passage The fuel-air surface is skewed similar to the fuel-air surface in the middle of the inlet port Results from air buffer case

37. Close-up view of inlet port opening to rotor passage – with & without air buffer Fuel sent in from first inlet segment Air sent in from first inlet segment

38. Boundary conditions obtained from 1-D detonation model. The present case is studied for deflagration and 2-D  incompatible with 1-D BCs Modified BCs to velocity  high flow causing choke exhaust Used case to study general effect of fuel-air distribution on combustion Setup - combustion case

39. Combustion with fuel-air coming in from first three inlet segments Ignition port

40. Combustion air coming in from first inlet segment acting as air-buffer Ignition port

41. Premature ignition when fuel-air mixture from first three inlet segments due to hot products from previous cycle Presence of air buffer as first inlet segment prevents premature combustion Results of combustion case

42. Skewness (tangential non-uniformity)

43. Comparison of penetration of fuel for both configurations

44. Developed methodology for 2-D wave rotor simulation Compared with published 2-D simulation results by Welch (1997) Used commercial solver for CFD simulations Applied methodology to ICWR Studied multidimensional factors affecting fuel-air distribution on few configurations With no air buffer – skew can be affected by timing, total inlet conditions Premature ignition can be prevented by air-buffer To do a higher fidelity simulation, of a given wave rotor configuration, include a finer grid based on NASA 4-port wave rotor and geometry and boundary conditions obtained from one-dimensional deflagration. Conclusions