Week 4.1: Project - Steady state simulation of flow over a throttle body

Steady-state simulation of flow over a throttle body

Aim:

To set up and run the steady state simulation for flow over the throttle body using Converge.

Objective:

• The objective of this project is to set up the steady-state simulation for flow over throttle using Converge Studio and run the simulation using Converge.
• The CAD model of the Elbow pipe with a Butterfly valve is used for the simulation.
• The purpose of this simulation is to observe the effect of the throttle on the flow through the elbow pipe. The butterfly valve will act as the throttle for this simulation.
• This case is simulated for a fully open throttle profile.
• Post-process the result using Paraview

Introduction:

A throttle is a mechanism used to control the fluid flow through a pipe by constricting or obstructing the flow.

A throttle is placed in the air-fuel intake manifold of the internal combustion engine to control the amount of air-fuel mixture flowing into the combustion chamber.

Mostly in the internal combustion engine, the Butterfly valve is used as a throttle body. A butterfly valve is a quarter-turn rotational valve which has a disc mounted on a rotational shaft.

Its simple mechanism, very easy to operate and quick response make it ideal to use as a throttle for an IC engine.

The throttle valve restricts the flow when it is fully closed profile. But in the fully open profile, due to the thickness of the disc, it constricts the flow leading to flow energy losses.

We can use CFD tools to simulate the flow over a throttle body to observe and visualize the effect of the throttle body on fluid flow.

Procedure:

Simulation setup in the Converge Studio:

• Import the CAD model (STL file) of the elbow pipe into the Converge Studio.

• Delete the outer wall of the pipe as they have no purpose in the current simulation.

• Close the open edges to create a water-tight geometry.

• Define the boundaries and assign the name for the boundaries.

• Perform a diagnostic test to look for geometrical errors if any.

• Begin the case setup for the simulation with the Application type as Time-based.

• For the Materials, set Air as a Predefined mixture and uncheck all the options except Gas simulation as we are interested in gas simulation only.

• For the initial condition, assign the region inside the pipe.

• Set up the boundary condition for each boundary.

BOUNDARY CONDITION

Inlet

1. Boundary Type: INFLOW
2. Pressure: 1.5 Mpa
3. Velocity: Zero Normal Gradient
4. Temperature: 300 K
5. Species: Air

Outlet

1. Boundary Type: OUTFLOW
2. Pressure: 1 Mpa
3. Velocity: Zero Normal Gradient
4. Temperature: 300 K
5. Species: Air

Pipe Wall

1. Boundary Type: WALL
2. Wall motion type: Stationary
3. Surface movement: Fixed
4. Law of Wall
5. Temperature: Zero Normal Gradient
6. Turbulent Kinetic Energy:
7. Turbulent Dissipation: Wall Model
8. Near Wall Treatment: Global

Throttle Wall

1. Boundary Type: WALL
2. Wall motion type: Rotating
3. Surface movement: FIXED
4. Law of Wall
5. Temperature: Zero Normal Gradient
6. Turbulent Kinetic Energy:
7. Turbulent Dissipation: Wall Model
8. Near Wall Treatment: Global

• In the Run Parameters, choose a Steady-state solver for the solver and Full hydrodynamic for simulation mode as shown in the figure below for the steady-state simulation.

• Check the Steady-state monitor to stop the simulation when it reaches steady-state.

• Set up the following setup in the Steady-state monitor setting as shown in the figure below.

• Setup the Simulation Parameter setting as shown in the figure below.

• For the Solver Parameter, select PISO for the solver scheme and Density-based solver type.

• For the Turbulence modelling, opt for RANS with the RNG k-epsilon model.

• In the Grid Control case setup, opt for Fixed Embedding.

• Set the Base Grid size as 0.04m as shown in the figure below.

• Setup the embedding near the throttle wall with the scale of 2 and 2 embed layers to capture the boundary layer phenomenon near the throttle wall.

• Export the input file to the working folder.
• Open the working folder in the Cygwin terminal and run the simulation using the following command. ‘mpiexec.exe -n 4 converge.exe restricted </dev/null> logfile &’
• Post-process the results using ParaView.

Results:

Mesh:

Pressure Plot

Static pressure Inlet vs Outlet

Total Pressure Inlet vs Outlet

Pressure Contour

Velocity Plot

Average velocity Inlet vs Outlet:

Velocity Contour:

Mass Flow rate Plot

Mass flow rate Inlet vs Outlet:

Total cell count:

Cells allocated to different processors

Conclusion:

From the above velocity and pressure contour plots, we have 3 observations

- Near the upstream face of the throttle valve wall, there is a sharp increase in the pressure indicating the stagnation region near the throttle valve wall.

- Narrow region in the top and bottom of the throttle valve acts as a constricted region. We observed a pressure drop leads to an increase in fluid velocity in the constricted region.

-A sudden decrease in velocity is observed in the region near the downstream face of the throttle valve wall. This region is the wake region.