Transient simulation of flow over a throttle body

In this project, we are going to simulate flow in an elbow joint that contains a throttle valve. This mechanism is widely used in carburettors and in the piping system in ships. In this project, we will study the flow patterns in the fluid due to the movement of the throttle valve.

 

Main Objective

To simulate transient flow over a throttle valve and post-process the results using ParaView.

 

Geometry

The pre-modelled throttle body was imported into Converge and the geometry was inspected for any surface errors or open edges. After fixing all the errors, the boundaries were flagged and the case was set up.

The elbow pipe with throttle geometry

A meshed view of the pipe

 

Throttle Movement

The throttle valve was programmed to rotate by 25° for 0 – 2 ms and stay in that position for 2 ms; later move back to its original position within the next 4 ms. The completed valve movement can be visualized with the help of the below animation.

 

 

 

Mesh:

Mesh size of 2e-3 was provided in X, Y, Z directions with a fixed embedding of 3 layers and a scale of 3 near the throttle boundary.

 

 

The mesh changes during the flow can be visualised with the help of below mesh animation:

 

 

 

Initial and Boundary Conditions:

The initial and boundary conditions were set to:

Inlet Pressure: 150000 Pa

Outlet Pressure: 100000 Pa

Elbow Wall Temperature: 300K (Law of Wall)

Throttle Wall Temperature: 300K (Law of Wall)

Solver: Transient Flow Solver

Fluid under consideration: Air (O2 + N2)

 

Simulation Time Parameters:

Start Time: 0 ms

End Time: 10 ms

 

Results:

Post processed results are as follows:

 

1. Velocity Profile:

The velocity of the flow over the throttle valve was visualised using ParaView.

The maximum velocity of 310 m/s was recorded when the valve was at 25° from its initial open position where the flow area was obstructed by the valve movement.

 

  

                                                      Velocity Stream flow over throttle valve

 

                                                                        Velocity Contour

 

  

                                                                       Velocity Glyph

 

2. Pressure Profile:

The pressure distribution during the valve movement can be visualized with the help of the below animation recorded using ParaView.

Initially, when the valve was in open position, there was not much pressure difference in the fluid between the entry and exit points of the throttle valve. As the valve began to rotate, the side of the valve facing the flow experiences maximum pressure of 1.5 bar. This pressure is due to the fact that the total kinetic energy of the fluid is converted into pressure energy when the flow is obstructed.

 

  

                                                         Pressure Contour over the throttle body

 

 

                                                      Pressure distribution on the throttle valve

 

3. Mass Flow rate and Average velocity at Inlet and Outlet

From the below graphs, it can be noticed that the mass flow rate and the velocity changes drastically when the valve is changing position in the first 2ms, remains constant when the valve holds its position between 2-4ms and gradually increases as the valve moves back to its initial position and remains constant when the valve has reached its original position.

 

 

4. Total Cell Count

Converge accounts for the change in geometry by generating mesh for each second, resulting in different cell counts when the valve is moving. For phases where the valve is stationary, the cell count remains constant which can be observed between 2-4 ms and 8-10 ms when the valve is not moving.

 

Conclusion:

By understanding the flow behaviour when the throttle moves, we can calculate how to control the flow input such that the output conditions are favourable. For example, if we require the fluid to have high outlet pressure, we can adjust the throttle movement accordingly. We can also further experiment and study flow behaviour when the throttle is opened at different angles.