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Wave Rotor Research Group-IUPUI Prediction And Design Of Fuel-Air Mixing in a Combustion Wave Rotor Using Two-Dimensional Unsteady Moving Mesh Flow Computation.

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Presentation on theme: "Wave Rotor Research Group-IUPUI Prediction And Design Of Fuel-Air Mixing in a Combustion Wave Rotor Using Two-Dimensional Unsteady Moving Mesh Flow Computation."— Presentation transcript:

1 Wave Rotor Research Group-IUPUI 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 Wave Rotor Research Group-IUPUI Objectives of the present work 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

3 Wave Rotor Research Group-IUPUI Introduction 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)

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

5 Wave Rotor Research Group-IUPUI Internal Combustion Wave Rotor (ICWR) Wave Rotor CompressorTurbine Schematic of ICWR Constant Volume Combustion

6 Wave Rotor Research Group-IUPUI 2D & 3D view of wave rotor

7 Wave Rotor Research Group-IUPUI Pre- and Post- Processing Package 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)

8 Wave Rotor Research Group-IUPUI Results of two grid packages Star-Design IUPUI in-house code

9 Wave Rotor Research Group-IUPUI Past 1-D simulations Paxson and Nalim 1-D code (1997)Berrak and Nalim Detonation 1-D code (2004)

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

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

12 Wave Rotor Research Group-IUPUI Arbitrary Sliding Interface

13 Wave Rotor Research Group-IUPUI Estimating Artificial Diffusivity 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

14 Wave Rotor Research Group-IUPUI Physical Diffusivities: Thermal diffusivity for air ~0.00002 Turbulent diffusivity for ICWR case ~0.5 Distance along tube TiTi Cell size (cm) Artificial diffusivity (m 2 /s) 2.50~1.5 1.00~0.5 0.25~0.05 Shock tube

15 Wave Rotor Research Group-IUPUI Hardware Resources AVIDD Linux Cluster –Huge Scratch space –Batch Scheduling –Accessible from outside of network (SSH) Dual CPU PC –Quick turnaround –Debugging –Manual decomposition 15

16 Wave Rotor Research Group-IUPUI Methodology Development 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

17 Wave Rotor Research Group-IUPUI Grid Resolution

18 Wave Rotor Research Group-IUPUI WelchIUPUI Rotor Passage Grid Dimensions (nodes)115 x 41123 x 41 Rotor Wall Tangential Spacing (in cm)8.90E-039.00E-03 Rotor Wall Tangential Spacing (in cm)6.40E-026.20E-02 Inlet & Outlet Port Grid Dimensions (nodes)85 x 151 Low Pressure Exhaust Port Dimensions (nodes) 85 x 16585 x 151 Port Wall Tangential Spacing (in cm)8.90E-039.00E-03 Rotor/Port Interface Axial Spacing (in cm)6.40E-026.00E-02 Rotor Interior Axial Spacing (in cm)0.25 Grid discretization comparable to Welch (1997)

19 Wave Rotor Research Group-IUPUI Computed instantaneous total temperature 400 1200 IUPUIWelch-2D

20 Wave Rotor Research Group-IUPUI 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 Wave Rotor Research Group-IUPUI Computed instantaneous static temperature contours showing close up view of passage gradual opening process and 2D flow features IUPUIWelch-2D

22 Wave Rotor Research Group-IUPUI Fuel-Air Mixing in an Internal Combustion Wave Rotor (ICWR) 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

23 Wave Rotor Research Group-IUPUI 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 Wave Rotor Research Group-IUPUI Rotational speed of the rotor (rpm)4100 Number of cycles per revolution1 Rotor angular velocity (rad/s)429.2 Number of passages20 Passage length (meters)0.7747 Mean passage width (meters)0.062 Mean radius (meters)0.199 Gap b/w rotor end wall & blade (meters)0.005 ICWR geometry

25 Wave Rotor Research Group-IUPUI Grid Resolution Ignition port

26 Wave Rotor Research Group-IUPUI Inlet species compositions Air Inlet Fuel-air Inlet Fuel or Air Inlet Direction of Flow Species Mass Fractions

27 Wave Rotor Research Group-IUPUI Non-Combustion Pressure waves for time converged solution 10.5 KPa 182.6 KPa

28 Wave Rotor Research Group-IUPUI Fuel distribution for one-dimensional and two-dimensional Red indicates stoichiometric fuel-air mixture, the desired fuel fraction for the ignition region

29 Wave Rotor Research Group-IUPUI Shape of fuel-air interface 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

30 Wave Rotor Research Group-IUPUI Close-up view of first inlet segment opening to rotor passage “ tufts indicate flow vectors relative to rotor” V abs V rel General velocity diagram Modified relative velocity diagram for present case V abs V rel

31 Wave Rotor Research Group-IUPUI Developing more uniform fuel-air interface 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

32 Wave Rotor Research Group-IUPUI Reduced total pressure at first inlet segment

33 Wave Rotor Research Group-IUPUI Increased total pressure at first inlet segment

34 Wave Rotor Research Group-IUPUI Results of varying total pressure at first inlet segment 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

35 Wave Rotor Research Group-IUPUI Adding air-buffer as first inlet segment

36 Wave Rotor Research Group-IUPUI Results from air buffer case 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

37 Wave Rotor Research Group-IUPUI 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 Wave Rotor Research Group-IUPUI Setup - combustion case 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

39 Wave Rotor Research Group-IUPUI Ignition port Combustion with fuel-air coming in from first three inlet segments

40 Wave Rotor Research Group-IUPUI Combustion air coming in from first inlet segment acting as air-buffer Ignition port

41 Wave Rotor Research Group-IUPUI Results of combustion case 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

42 Wave Rotor Research Group-IUPUI Skewness (tangential non- uniformity)

43 Wave Rotor Research Group-IUPUI Comparison of penetration of fuel for both configurations

44 Wave Rotor Research Group-IUPUI Conclusions 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.


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