Week 4.2: Project Transient simulation of flow over a throttle body
Aim: To set up transient simulation of flow over the throttle body.
Procedure:
To create / import geometry:
1) click on file > import > import STL then select the path of.STL file to be imported and click import.
2) After importing geometry delete the thickness and patch the open edges. to delete thickness Repair>Delete>triangle select triangle using by angle and click apply to delete surface. to patch open edges Repair>Patch>Free Edge Loop select the edge to be patched and click apply.
3) Click on diagnosis to check for any errors. If all the normals are pointing inside the geometry then we can move ahead if not we can flip the orientation of normals inside using Transform > Normals > Propogate change from a single triangle select a triangle and hit apply.
4) Next step is boundary creation.
Case Set up:
1) Click on begin case set up to start case set up select application type as time-based and Predefined mixture as the air. Uncheck reaction mechanism and check species.
2) In run parameters select solver type to be the transient-state solver. uncheck used shared memory.
3) In simulation time parameters enter the start time as 0 sec. To calculate the end time measure the length of the elbow and check the average velocity at the inlet then divide the length of the elbow by the velocity.
t=(length of the elbow)/(Avg. Velocity at the inlet)
l= 0.176m
v= 80 m/s
t=0.176/80
t=0.0022 sec
4) It takes 0.0022 secs for the flow to flow from the inlet to the outlet we want the flow to simulate for 3-4 times of that so End time =t*4
End time =0.0022*4
End time = 0.0088 secs
5) Set inlet as inflow boundary Inlet - Inflow P= 1.5e5Pa T=300K Species: Air
Outlet - Outflow P=1e5Pa T=300K Backflow species: Air
Elbow_Walls - Walls
Throttle- Walls and select the law of the wall
In the transient state we want the throttle body to rotate by 25 degrees from 0-2ms to 2-4 ms it should stay at that position and from 4-8 ms it should get back to its original position. For that first, we need to find the axis of rotation and centre of rotation of the throttle body.
i) To find the axis of rotation Measure>Direction>Arc normal and select any three points on the top face of the cylinder and click apply. copy the coordinates of arc normal and paste them in the boundary condition tab.
ii) To find the coordinates of the arc centre copy the coordinates named arc centre and paste them into the boundary condition tab.
iii) after adding the rotation axis and rotation center we need to add the rotation rate of the valve. for that click on the use file as we need to change the rotation rate according to the time parameter so add four rows to be
Time | Angle
0 0
0.002 25
0.004 25
0.008 0
and then name the file as throttle_position.in and click on accept.
6)Add new reagions in reagions and initialisations and add species to be air and click apply.
7) In the Physical model select RNG k-εε keeping other values as default.
8)The next step is to create a mesh size. While creating mesh keep cell count within the limit to avoid memory overflow. Click on grid control then check on fixed embedding. In embedding select entity type as boundary and boundary ID as Throttle. Select Mode to be permanent and scale as 3 and layer to be 2.
9) In output files change the time interval to write 3D output files to 1 ms so that we can get 10 3-D output files and time interval to write text output files to be 1e-6 secs.
10) Input files are ready for processing. Click on final validation to check for any errors.
Processing input files:
1) Click on file > export > input files
2) Copy and paste licence.lic and mpiexec.exe file in the folder of input files
3) Open Cygwin browse to the input files folder
4) Enter the following commands
mpiexec.exe -n 6 “C:\Program Files\Convergent_Science\CONVERGE\3.0.16\bin\intelmpi\converge.exe” restricted
5) After completion of the process.
6) Copy and paste the post_convert file in the output folder in the cygwin Enter command
mpiexec.exe -n 6 post_convert
7) Enter the Name for the case selection
8) Enter file type to export as Paraview VTK in-line binary format
9) Select yes to put boundary surface output
10) Include all files for post-processing
11) Include all cell variables
Post-processing of files:
1) Open Paraview for post-processing and open a folder named output and open the file with extension .vtm and click apply.
2) Click on slice and along Z normal uncheck triangulate slice and show plane.
3) Select velocity click play and check on visibility change.
Results:
Mesh-
Velocity:
The velocity around the throttle is different, at the edges of the axis along which the throttle rotates velocity is high due to the narrow area. Throttle rotation reduced the area available for the passage of the fluid, which resulted in increased velocity in those regions.
Pressure:
When the throttle valve is at its extreme position it is blocking the airflow which is resulting in the formation of two regions high-pressure region and low pressure region.
Velocity:
Pressure:
Mass flow rate:
The mass flow rate has both positive and negative values due to the conservation of mass at the inlet and outlet.
Total cell count:
The mesh is moving along with the rotation of the throttle causing variation in cell count during the simulation. From 0.002 sec and the 0.004-sec throttle is at a stationary position resulting in the constant cell count.
YouTube:
Throttle Position: https://youtu.be/Gk0NIlEyK7Q
Velocity: https://youtu.be/uWbqzVovF3E
Pressure: https://youtu.be/4u8cHPh2yI8
Streamlines: https://youtu.be/DwO0ozCKZp8