Simulation of flow through a throttle body Steady state

FLOW OVER A THROTTLE BODY: STEADY STATE

The objective of this project is to simulate the flow through a throttle body in steady state conditions. The throttle body is designed using external CAD software and is imported and cleaned for the particular simulation using CONVERGE. The flow of processing is as follows:

1. Import given geometry in .stl format.
2. Given model is edited as per needs.
3. The model is cleaned and necessary boundaries are given.
4. Input files exported to working directory.
5. Converge executable used to produce output files
   • Processors used: 4
   • Series processing
6. All output files post processed using CONVERGE.
7. Simulation run through Paraview and results are obtained.
8. Plots are derived using CONVERGE.

CASE SETUP

The given model:

Dimensions of geometry:

X: 0.107 m

Y: 0.12 m

Z: 0.019 m

As we can see, the geometry is hollow and has a thickness. For our project, we do not need this thickness. Hence, we can select the outer boundary and the extra geometry along with it, and delete it using the delete option or we can use the shortcut \'D\' key too. This creates a pair of open edges at each opening and those ends must be closed. Through repair option, we can patch those edges for a complete geometry with no errors.

After this, the geometry dimensions are changed to:

X: 0.106 m

Y: 0.12 m

Z: 0.017 m

Now, we can assign specific boundaries for each surface. The outer wall is named elbow wall and the throttle is selected as a separate surface and a boundary as a whole.

Given changes of parameters are:

• Fluid medium: Air
• Inlet Pressure(Pa): 1.5 bar (1.5xe^5 Pa)
• Outlet Pressure(Pa): 1 bar (1xe^5 Pa)
• Mesh sizes: dx = dy = dz = 0.002 m
• Embedded mesh along the boundary condition: Throttle
  • Scale: 3
  • Embedded Layers: 2
• Solver used: Pressure based steady state solver
• Time steps:
  • Min time step = 1e-9 s
  • Initial time step = 1e-9 s
  • Max time step = 1 s
• Cycles: 0 - 15,000 cycles
• All other parameters are default.

After the case has been completely set up with appropriate boundaries, the input files are exported to the specific directory-> throttle body flow -> Steady state.

Then, converge executable is run through Cygwin terminal. After the output files have been written, they are post processed using CONVERGE itself.

After that, group files in .vtm format are loaded in paraview to view the 3D output files and simulation configured.

RESULTS

The simulation results are rendered using Paraview after post processing using CONVERGE.

The throttle position for steady state simulation of flow is unchanged:

The mesh:

After the slice option is used for a 2D representation of flow, the throttle visibility is increased and incorporated for a better view of the simulation results.

Simulation:

As we take the velocity contour into account, we can see an unrestricted flow across the throttle body and an increase in velocity near the end of the throttle section at neck. This is due to the reduced area of cross section along the neck turning point and the position of the throttle. Normally we would have nuts and bolts sealing this area and a shaft passing through the throttle to hold it still. Here for simplicity, we get a constricted flow of air resulting in a drop in pressure and increase in velocity at specific regions alone.

The embedded mesh across the throttle:

A closer look at the embedded mesh of the throttle and how it shows the velocity profile and magnitude at the neck. To get a better perspective, let\'s use the glyph option to see how the velocity vector field interacts with the throttle.

Velocity vector field:

For a reduced scale factor, we can clearly see the incoming flow of air through the top and the constriction of flow at the neck and the drop in velocity when it hits at the middle of the throttle as an obstacle. There are no other backflows as the throttle gives way to the flow afterwards.

Pressure contour and vector field:

The pressure vectors with the velocity gradient in the background gives the view of how pressure drops behind the throttle and the constriction at neck that leads to the sudden increase in velocity due to reduced area of cross section.

Velocity and pressure plots using CONVERGE:

After the simulation results have been seen using Paraview, CONVERGE can be used to read the output files and compare results across the inlet and outlet of the throttle body in steady state.

As we can see, the velocity and pressure is conserved across the cycle domain and the velocity reaches a steady state of convergence after around 6000 cycles itself. Hence, the simulation could be run with lesser cycles too which would reduce it\'s computational load and give accurate results as well.

Cycles per rank and Mass flow rate:

The mass flow rate also converges fairly early and the simulation is ran through four processors simultaneously. Hence with a total cell count of nearly 40,000 and roughly around 10,000 cells each, the simulation has an accurate representation of flow model.

This is the total time taken for the simulation to complete and it could have been reduced with fewer cycles to compute and the time taken will also increase for a finer mesh or a transient state model, where the throttle position changes with respect to time to simulate transient results of velocity and pressure profiles.

INFERENCE:

In this project, we got to see the flow mechanics through a throttle body when the throttle does not move or is in a steady state. An animation is created of the simulation and posted on YouTube. We also got to see how pressure and velocity changes when an object interferes with the flow.