Transient simulation of flow over a Throttle Body using Converge CFD
Aim:
The major objective of this project was to perform a transient simulation for the flow of air over a throttle body when the throttle is moving at some angle in Converge Studio and post-process the results using ParaView.
Introduction:
The report contains a detailed description of the transient simulation over a Throttle valve using converge CFD software, solving it using CYGWIN and post-processing the result using ParaView. Various steps are discussed in this report while making a case set up for the case study. This report contains a detailed description of the case study with grid sizing, line plots, and contours. In this simulation, the throttle valve is rotating by a given angle during the simulation.
The throttle inside the pipe is aligned parallel to the plane of the pipe. The blue face represents the throttle valve, pink represents the outlet and dark green represents the inlet whereas light green is elbow wall.
In this Project, the throttle valve is rotating about its axis during the time of the simulation. The rotation angle is dependent on the function of time and position of angle.
Rotate by `25 degree` from 0 to `2 ms`
Rotate by `25 degree` from 2 to `4 ms`
Rotate by `25 degree` and come back to original position by `8 ms`
1.Geometry Creation
First of all, the Elbow body along with throttle step geometry was setup using converge CFD software. The geometry was separately prepared using different CAD package ie. Solidworks, then .stl file was imported to Converge Studio to set up the case study.
Image 1: Elbow body along with Throttle
*Each face of the step was split into multiple triangles.
The Geometry can be downloaded from this link: Elbow Geometry
To create the geometry, the geometry was uploaded from the different CAD software package. Then the geometry clean up was done along with inlet and outlet catch creation. All the normal vector were pointing out for this geometry, so we wanted it to point inside and normal to each surface. Normals point the direction of the fluid region generally. The command "Transform" was used to make the normal inside pointing the direction of the fluid region.
The Geometry was a check for if the geometry has any open surface.
Then the normal edge checked and from the diagnostic dock, everything was checked.
2.Boundary Creation
After creating the elbow Geometry, The Boundry tag was created along with different boundary id and coloring. A total of 4 different boundaries tag was created for so many different split triangles of the elbow with each face split into multiple triangles. To create the boundaries naming, the "Boundary" command in the "Geometry" dock was used, and then the faces were appointed to appropriate tags along with id.
Image 2: Boundary creation representing the different id and color.
The four different boundaries were Inlet, Outlet, Elbow Wall, and Throttle.
3.Case-Study Setup
The various parameter was considered while setup this case study. The case study setup dock was used to set up the problem which appears on the right-hand side of the converge studio.
Image 3: Case Setup Dock.
3.1 Application Type:
In order to run a steady-state simulation, firstly, under the Application type in the setup tree, a "Time-based" simulation must be selected.
3.2 Materials:
Under the material tab "Gas simulation" was selected and "Air" as a predefined mixture.
Gas: Air
Global Transport Parameters: Fixed value
by default, the following value is considered.
Prandtl Number : 0.9
Schmidt Number : 0.78
Species: Oxygen-O2 & Nitrogen-N2
Reaction Mechanism (mech.dat) was selected for this problem.
3.3 Simulation Parameters
The Transient solver was selected for running this case study along with a "Pressure based" solver.
Calculation
Pipe length=0.2m
Average Velocity=185m/s
Speed=Distance/time
therefore, Time=0.00123 sec
we are simulating ten times of flow through time that is 10ms
The Following Simulation parameters were selected for running this simulation.
3.4: Boundary Conditions
In this tab, The volumetric region and physics for each boundary were defined.
| Boundary_Name | Boundary_Type | Paramter_Defined | Boundary ID |
| 1.Inlet | Inflow | 150000.0 Pa | 3 |
| 2.Outlet | OutFlow | 100000.0 Pa | 4 |
| 3.Elbow Wall | Wall |
Specified Value(300k) Law of wall |
1 |
| 4.Throttle | Wall |
Specified Value(300k) Law of wall |
2 |
In this problem, the throttle is made move at some angle about an axis of rotation so the coordinate points have been assigned in order to rotate it.
Rotation Center: -0.0761535, 0.0390774, 0.0201742
Rotate About: -0.794573, -0.607168, 0
In this Project, the throttle valve is rotating about its axis during the time of the simulation. The rotation angle is dependent on the function of time and position of angle.
Rotate by `25 degree` from 0 to `2 ms`
Rotate by `25 degree` from 2 to `4 ms`
Rotate by `25 degree` and come back to original position by `8 ms`
3.5: Initial Conditions and Events
Volumetric Region was created in order to assign this to all the boundary tag.
Species:- O2 (0.23) & N2 (0.77)
Pressure :101325Pa
Temperature:300K
3.6: Physical Models
A turbulent model was selected out of so many models.
3.7: Grid Control
The case study was run using a fine mesh grid size. So different case study was set up in order to study the effect of value when the mesh is more refined.
Base mesh sizes are,
| S.No. | Dx(m) | Dy(m) | Dz(m) |
| 1 | 0.002 | 0.002 | 0.002 |
Fixed embedding was done in order to capture more cells near to throttle in order to get more precise data.
Scale : 3 & Embed Layers: 2
3.7 Output/Post-Processing
Post-Variable Selection- Existing value
Output Files- Time interval for writing 3D output files-0.001 s
The time interval for writing restart files -0.01
The case study was solved using CYGWIN and the post-processing was done in ParaView.
Meshed Geometry
Case Study: dx=dy=dz=2e-3 m
Image 3: Meshed Geometry with Fixed Embedding on Throttle.
Result
Line Plots & Contours
Velocity Data
Pressure Data
Mass Flow Rate
Total Cells
Conclusion
Many things can be noted from this simulation:
The flow just behind the throttle is thrilling due to less gap between valve and elbow wall and this also causes the pressure drop therefore there is a drastic drop in velocity just behind the valve. In the total number of cell plot, the data is always changing its due to because of changing mesh due to valve movement.
The Fixe embedding of mesh provides enough cell capture which enables us to capture more data and mesh is properly oriented when the valve is moving.
The Case study can be downloaded from this link: Case Study TRANSIENT SIMULATION