Project Transient simulation of flow over a throttle body

Transient simulation of flow over a throttle body

• Aim:

- Perform transient simulation flow over a throttle body.

- Throttle body is rotated about 25degrees.

- Post process the results and plot the necessary graphs and contours.

- Create a flow animation to depict the flow characterestics and show the movement of throttle body.

• Procedure:

1. Upload the stl file onto converge studio, remove the thicknes by using the delete option under repair.

2. Close the open edges by creating inlet and outlet surfaces to close the geometry.

3. Asssign boundary flagging for each boundary appropriately.

4. Assign throtlle boundary flagging by hiding the outer wall partially and then assign boundary to throttle by choosing surface select.

- Case setup:

1. Application type: time based

2. Materials:

a. Gas simulation: air

b. Global transport properties: Deafult

c. Species: O2 and N2

3. Simulation parameters:

a. Run parameters:

Transient solver, full hydrodynamic, compressible

b. Simulation time parameters:

- End time- 0.01 cycles

Calculating end time:

End time is calculated by analysing the flow time from the inlet to outlet and the inlet velocity at which the flow generates, by knowing these 2 parameters, we can calculate the end time.

Since, length of the pipe is approx 0.18m and velocity at inlet = 82 m/s

Therefore, end time = distance of pipe/ inlet velocity

Which implies, 0.18/82= 0.0021 sec

It takes 0.0021 secs for the flow to complete 1 cycle, we can have 4 cycles which is 4x0.0021= 0.0087 `~=`0.01secs

- Time step- 1e-6

- min time step- 1e-6

- max time step- 1

- Convection CFL number- 0.5

c. Solver Parameters-

- Solver type- density based solver

- Equations- pressure- change preconditioner to none

4. Boundary Conditions-

a. Inlet- Inflow

- Total pressure- 1.5e5 Pa

- Initial temp- 300K

- Species boundary condition- add air

b. Outlet- Outflow

- Pressure- 1e5 Pa

- Backflow - temp= 300k

- add air

c. Elbow wall - Walls

no slip condition- The contact region between wall surface and fluid region tends to create high friction and create a 0 velocity of fluid flow, and due to viscosity of fluid, the fluid layers tend to undergo shear stress and have high pressure and overlap on eachother which eventually forms a fully developed region where velocity is max and constant and having low pressure.

d. Throttle body: Wall- Rotating

Since throttle is a separate surface creating an obstruction it acts as a wall, and given a roatating angle of 25degree, therefore the rotation is assigned.

By measuring the arc center and arc normal, we can assign the center of origin and axis of rotation.

5. Initial Conditions and Events:-

- Regions and Initialization:

Pressure- 1.5e5 Pa

Temperature: 300K

Add- air

6. Physical Models:-

- RNG k-epsilon

7. Grid Control:-

a. Base Grid:

dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

b. Embedding:

- Boundary type, Near the Throttle body, permanent mode embedding.

Scale- 3

Number of layers- 2

Embedding is the means by which we can refine the mesh to a value that is lower than the prevalent base size. This is especially useful if we are looking to refine near wall to capture the boundary layer or the wake of a body more accurately.

8. Post-Processing:-

- Post Variable Selection:

Select the parameters needed to be post processed.

- Output files:

We need to set a time interval for the files to be saved during each set of iterations. It is best suited to have a min of 100 saved files for every simulation. Therefore we need to calculate the time interval for writing the output files based on our end time given in run parameters.

Restart files help in restoring the files if there is a sudden power cut/ crash which is not helpful or might end up loosing the entire data, therefore the restart files helps in resuming the simulation form the point we lost contact. Restart files time interval can be same as the writing files interval which is safe and healthy.

In this case- since the end time is 0.01, we can have a time interval of 0.0001 and the total files created will be 100.

• Results:

1. Mesh grid:

- Full body mesh:

- Throttle body mesh:

-Cell count:

- Throttle body mesh movement animation:

2. Mass flow rate:

3. Inlet:

- Total pressure:

- Static pressure:

- Average velocity:

4. Outlet:

- Total pressure:

- Static pressure:

- Average velocity:

5. Velocity contour:

- velocity streamline:

6. Pressure contour:

7. Velocity flow animation:

• Conclusion:

- Transient simulation flow over a rotating throttle body is achieved.

- It can be observed as the flow travels through the moving throttle body, pressure is increased at the inlet to throttle body region and a drastic decrease in pressure at the throttle body to outlet region.

- Wake region is formed on the throttle body dure to flow separation which is creating recurculation region.

- It can be obsereved that the ue of throttle body controls the air flow depending on the rotation of the throttle body which is useful in reducing fuel consumption.

- Embedded mesh is moving along with the throttle body movement which creates a lot of mesh regeneration, which can be observed the fluctuation of the cells in the cell count graph.