Week 4.1: Project - Steady state simulation of flow over a throttle body

Aim

The aim of this challenge is to simulate the flow over a throttle body inside an elbow

Objectives

• Simulation of flow over a throttle body
• Post processing of the results for flow variables

THROTTLE BODY

In fuel injected engines, the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main. The throttle body is usually located between the air filter box and the intake manifold, and it is usually attached to, or near, the mass airflow sensor. Often, an engine coolant line also runs through it in order for the engine to draw intake air at a certain temperature (the engine's current coolant temperature, which the ECU senses through the relevant sensor) and therefore with a known density.

The largest piece inside the throttle body is the throttle plate, which is a butterfly valve that regulates the airflow.A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term throttle has come to refer, informally, to any mechanism by which the power or speed of an engine is regulated, such as a car's accelerator pedal. What is often termed a throttle (in an aviation context) is also called a thrust lever, particularly for jet engine powered aircraft. For a steam locomotive, the valve which controls the steam is known as the regulator.

STEADY-STATE SIMULATION OF A THROTTLE BODY

Case Setup:

1. Open converge studio console
2. Drag and drop the throttle valve model in graphics panel.
3. To ensure better flow simulation, we delete the outer covering of the elbow wall>> select triangle entity selection>> choose angle mode>> select the outer elbow wall>> select delete
4. 
5. Follow the similar procedure for the inlet and outlet section as given in step 3.
6. 
7. 
8. The inlet and outlet section are open and will generate open edge error.
9. To remove the error we provide patching>> select edge tab>> select open edge mode>> go to repair section>> select the inlet and outlet edge>> select patch and the apply. The openings will get closed.
10. 
11. 
12. Go to option>> select bounding box. The dimension of the box will be highlighted>> change the scale to 0.001 in order to convert to meters.
13. The geometry is now created.
14. 
15. We conduct a diagnosis check to remove all the geometrical errors
16. 
17. Go to the right-hand side case set up option, there we will find many setting up option.
18. 
19. Select application option>>select time based option.
20. 
21. Go to materials>> select gas simulation >> click ok
22. 
23. Go to global transport parameters >> select ok.
24. 
25. Go to simulation parameters>> select run parameters>> choose steady state solver with full hydrodynamic case.
26. 
27. Go to steady state monitor>> provide monitor variable as mass flow rate>> select target type boundary>> select target as outlet
28. Provide the min no of cycles for steady state solver>> provide monitor delay start, sample size.
29. 
30. Select simulation time parameter>>provide end time as 15000 cycles>> provide initial and min time step of 1e-9 and max time step of 1
31. 
32. Go to solver parameter setting>> choose density based >> go to equation >>select pressure and set precondition to none>> go to solver control and define the cfl limit to 0.5
33. 
34. Go to boundary>> define all boundary region name with ID
35. For inlet > > choose inflow type
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37. 
38. For outlet > > choose outflow type
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40. 
41. For elbow wall > > choose wall type
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43. 
44. For throttle > > choose boundary type as wall
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46. 
47. Go to initialization>> choose region give name as region0>> specify the composition of species
48. 
49. Go to turbulent model>> select RNG kepsilon
50. 
51. For grid control>> provide the grid sizes in x, y, z direction as 2mm
52. 
53. Define fixed embedding to refine the grid at the throttle section>>select fixed embedding>>select boundary ID as throttle>>give embedding scale of 3 and layers 2
54. 
55. Go to post variable selection>> select the variables for post processing
56. Go to output files>> provide the no of output files to be dumped.
57. 

BOUNDARY CONDITIONS

Inlet boundary

1. Inflow Boundary
2. Pressure = 1e5 bar
3. Mixture - air
4. Temperature = 300 K

Outlet Boundary

1. Outflow Boundary
2. Pressure = 1 bar
3. Mixture - Air
4. Temperature = 300 K

Throttle

1. Wall Boundary
2. Wall Motion - Stationary
3. Temperature = 300 K
4. Turbulent Kinetic Energy - zero normal gradient
5. Turbulent Dissipation - Wall Motion
6. Turbulent Model - RNG K-Epsilon

Elbow Wall

1. Wall Boundary
2. Wall Motion - Stationary
3. Temperature = 300 K
4. Turbulent Kinetic Energy - zero normal gradient
5. Turbulent Dissipation - Wall Motion
6. Turbulent Model - RNG K-Epsilon

Simulation run:

1. Export all the case set up from the converge studio
2. Go to Cygwin>> go to desired path or directory
3. Type the command mpiexec.exe -n 4 converge.exe to run the simulation.
4. To post convert the output files, go to Cygwin>> type the command as ex -n 2 post_convert_msmpi_64.exe

Geometry:

Elbow joint contains the throttle body over which we are interested to see the flow over the body.

Mesh:

Mass flow rate:

The mass flow rate is high initially and becomes stable at 0.007kg/s after reaching 10000 cycles. The fluctuation of mass flow is due to variation of inlet static pressure and decrease in velocity. The outlet mass flow rate increases and becomes stable at

Density variation:

Inlet density variation is caused due to mass flow variation. The inlet density attains stability at 1.45kg/m3 after reaching 10000 cycles. At outlet section density increases and reaches stability at 1.3kg/m3 at 8000 cycles. The fluctuation is caused due to variation of mass flow at the throttle region.

Total pressure:

The inlet total pressure remains constant all over the cycles of iterations. The outlet pressure increases and becomes stable at 135000Pa after reaching 10000 cycles. This variation of pressure is due to mass flow moving at the outlet section from the corners of throttle wall and causing rise in total pressure.

Static pressure:

The inlet static pressure is very high initially and after encountering the valve gradually decreases and becomes stable at 12000Pa after reaching 10000 cycles. The outlet pressure remains constant because of less variation of mass flow at outlet.

Average velocity:

The inlet average velocity variation is very high at starting and then reaches stability at 190m/s after reaching 12000 cycles. The high outlet velocity is due to low is due to low static pressure difference at the throttle region.

Procesors used for computation:

The total no of cell count used for running the simulation is around 35518 cells, while in processor 0 no of cells used is 8998, for processor 1 no. of cell count is 8769, for processor 2 no. of cell count is 8996 and for processor 3 no of cell count is 8755. The simulation is run in parallel to reduce the computation time.

Discussion:

From the steady state simulation of throttle valve, it is seen that pressure at the inlet is higher than the outlet. The mass flow variation is encountered at the throttle valve front position. The velocity at the inlet position is higher, but some region of high velocity is seen to leak from the corner of the throttle section. At the outlet the flow seeration takes place from the throttle surface and the outlet velocity reeduces down to attain a steady state value . The density variation also a function of mass flow variation and pressure difference. The flow seperation can be seen to take place when pressure tends to drop down.

Conclusions:

1. The steady state simulation is performed to observe the effect of flow seperation across the region of throttle section. The maximum velocity of 3.2e2m/s is observed at the inlet and low velocity of 50m/s at the outlet.
2. The pressure variation is seen to be fluctuating at the inlet and while encountering the valve, the pressure rises up. The outlet pressure becomes low and further detaches the flow seperation.
3. The grid refinement is done at the throttle section to capture accurately the flow behaviour. With refinement the computational cell count is higher and time taken to complete the simulation increases.