Transient simulation of flow over a throttle body

In this challenge, flow over a throttle body is simulated under transient conditions using Converge 3.0. The throttle is completely open during the first 0.002 seconds and for the rest of the simulation, the throttle is at 25 degrees.

Physical Setup:

General	Transient State Pressure Based
Model	RNG k-`ε`
Materials	Air (77% N2, 23% O2)
Simulation Time	Start Time: 0 seconds End Time: 0.01 seconds Minimum Time Step: 1e-9 seconds
Boundary Conditions	Inlet (1.5e5 Pa) and Outlet (1e5 Pa) Elbow-Walls and Throttle (Walls)
Motion of Throttle	zero degrees until 2 ms and for the rest of the simulation 25 degrees

Flow of Project in Converge:

1. Provided geometry is dropped in the Converge workspace.
2. Boundaries are named using appropriate names.
3. Normal directions are checked to be in line with the geometry and flow.
4. Diagnosis is performed to check any discrepancies in geometry.
5. Then appropriate species are selected for the fluid.
6. Simulation Parameters along with the appropriate time steps are set.
7. Boundary conditions are set to the appropriate regions and their corresponding values.
8. The base grid and embedded layers of the considered step size are inserted along with respective directions.
9. Variables for post-processing and time intervals for writing the output and restart files are set and selected.
10. All the input files are stored at the desired location.
11. All the stored input files are executed using the command editor. These input files are executed by Converge Solver in the background.
12. Then the executed files generate the output folder in which data files after every selected cycle intervals are stored which are post-processed for the graphical results.

Geometry:

The elbow pipe geometry with the throttle valve is as shown below. Moreover, it shows how the throttle is rotated over the simulation.

Mesh:

Mesh along the z-plane and variation w.r.t rotation of throttle is as shown below. Mesh of size 0.002m is used as the base grid and 2 embedded layers with a scale of 3 are used near the throttle boundary.

Total Cells:

Here the total cells over the simulation time are shown. Cells vary with the rotation of throttle.

Velocity Contour:

Pressure Contour:

Streamlines of Flow over a Throttle Body:

Velocity vector over a Throttle Body:

Pressure at Inlet and Outlet:

Mass Flow Rate

Average Velocity

In the above animations, velocity and pressure contours are shown along the z-plane. Moreover, streamlines and velocity vectors are represented along with the various orientation of the elbow pipe to observe the pressure acting on the throttle valve. It is evident from the above animations that the pressure acting on the leading surface is higher as it obstructs the flow and low-pressure zone exists behind the throttle area (trailing surface) and there is the chance of the recirculation zone created near the trailing surface owing to low pressure. Furthermore, it can be observed from the other plots that the results are converged.

Endtime Calculations:

The end time for the simulation is guessed from the average velocity plot of steady-state simulations. Here the average velocity was 200 m/s and the length of the elbow is approximately 0.2 m. So the time for the fluid to flow through the pipe completely is `≈`0.001s (i.e., 0.2/200). In order to observe the flow of 10 full flows the end time is set as 0.01s.