Week 4.2: Project - Transient simulation of flow over a throttle body

Week 4.2 Challenge – Trasient Simulation of flow over throttle body

Aim: - Transient simulation throttle valve inside the pipe with difference in pressure.

Objective: -

1. To study the importance of throttle valve in flow simulations.
2. To set up the transient simulation for throttle valve.
3. To create the embedding mesh near to throttle valve for better convergence.
4. To post process the results from the simulation.
5. To plot the graph of pressure, mass flow rate and velocities.

Introduction: -

To regulate the flow inside the pipe and to maintain the pressure across the domain throttle valve are used. This valves are operated manually or automatically through sensors and actuators. The application of throttle valve is seen in engine to actuate flow inside the cylinder and maintaining it according to applications. In engine the flow of coolant is also regulate by the butterfly valve which is one of the throttle valve in action. The throttle valve assembly is inserted between the two pipes where they are joined.

Solution Methodology: -

The transient simulation is setup for this problem. The geometry comprises of throttle valve inside and it is in three-dimension structure. As it is a flow simulation the thickness of pipe is not required. For this simulation, the rotation of throttle valve is required because of transient simulation does allow to rotate the valve for cycles. In converge studio the pre-processing is done for creating domain for fluid inside the pipe. The patch option is used to create the closing face for inlet and outlet. The simulation is run for 0.01 seconds.

Pre-Processing: -

1. Geometry

The geometry is imported directly in the converge studio by drag and drop method. The geometry is in the millimeter by default but the converge work in SI unit hence it is required to scale the geometry in meters.

Using the geometry transform option in which scale tool is used to convert the dimension into meters. The scale factor is 0.001 is applied.

After completing the scaling of the geometry, it is required to clean the geometry by closing the flow domain. This is done by finding the boundary with open faces.

As it stated earlier, the thickness of body is not required for the simulation. Hence the outer faces of the body are need to be deleted. Similarly, the faces with open edges need to be patched. This can be done using hotkeys after selecting the face by angle options. Or user can go to repair tab in which delete option can be used to delete the specific face in geometry.

After deleting the surface which are not required for the simulation, it is necessary to patch the open faces. This can be done using the open edge option in the selection toolbar which only allows to select the open edges present in the geometry. The patch option can be find out from the repair tab in which patch option present. The patch option capture the open edge and connect it with creating a face. This has to be done on the both side of elbow to make it as inlet and outlet face.

2. Boundary Creation

The creation of boundary in the converge studio is the main aspect to for meshing the geometry. As converge use mesh free method like cut cell meshing, it requires enclosed geometry for successful operation. The boundary creation is done in the boundary tab of the geometry setup section in which flag option is used. Four boundary are created in the setup which are wall, throttle, inlet and outlet. The wall is selected as elbow outer space, throttle is selected as the body inside elbow. The selection of body inside elbow can be done by hiding elbow after assigning to the boundary which make only throttle and other faces to be seen. After this the remaining two faces can be selected as inlet and outlet.

3. Case Setup

A) Type of Application of Simulation

The simulation type for the problem is transient in nature. Which is a time based approach.

B) Material type

The fluid for the simulation is simply Air without considering the species input file as it was not required.

C) Simulation Parameter

The solver setup is being set up to transient with simulation mode with as full hydrodynamics. The gas flow solver is consider as compressible in nature.

The simulation will be treated as pressure based approach as the velocity of the flow is very low. The Navier-Stoke pressure velocity scheme is consider as PISO as it mostly work for irregular mesh with better convergence.

The simulation time parameter for the problem is consider as 0.01 seconds. The maximum CFL limit for the problem is again consider as 1 for remove blowout of simulations.

D) Boundary Conditions

i] Inlet

ii] Outlet

iii] Wall Elbow

iv] Wall Throttle

In this case of transient simulation there is need of rotating the throttle valve because of conditions. To rotate the valve in the prescribe location it require rotation center and the axis around which it is rotating. This co-ordinate can be taken from the converge studio itself using 'Arc Normal' Method. It allows user the measuer the rotating center and rotation axis of the part.

Step 1- Hide the other faces of Throttle.

Step 2- Use of Arc Center Method.

In this method user has to select the three vertex location which will provide the required co-cordinates.

After selecting the three vertex, one has to click apply in the message box it will show the co-ordinates

This information has to be feed in the throttle boundary condition with an input file which have the co-ordinate data also the time data with respect to amount of angle by which throttle has to be move

The motion of throttle valve is given below:

From 0 to 2 milisecond throttle will move by 25 degree

From 2 to 4 milisecond throttle will stay at 25 degree

from 4 to 8 milisecond throttle will come to original position.

It is important to set the input file as .in format or it will not take into account.

E) Initial Conditions and Region

For the PDE to solve, it required intial conditions and boundary conditions. For this problem pressure and temperature are consider as initial conditions. In the convege studio it is necessary to create the region before assigning the boundary conditions because in the boundary condition one has to select the region associate with respective boundary conditions hence it is better practise. The air has to be taken into consideration for the region of interest for the simulations.

F) Meshing

The meshing parameter for the problem is consider as 2mm. The area near the throttle is slender, to capture the flow parameter near the throttle valve it is necessary to create more number of element. This can be done by creating embedding mesh in the region near throttle valve. The parameter for embedding is given below:

G) Output files

The total output files required for simulation will be something around 100. Hence the time interval to write 3D files can be calculated as:

Time interval for Writing 3D output files = 0.01/100 = 0.001

4. Solution

The solution of problem can be start using Cygwin application in which command 'mpiexec.exe -n 8 converge.exe restricted' is used to excute the simulation. The 8 represent the number of processor used in the simulation.

5. Results

1) Mesh in Simulation

2) Mesh Near the Throttle Valve

3) Velocity Contour at 2 Milisecond

4) Velocity Contour at 4 Milisecond

5) Velocity Contour at 8 Milisecond

6) Pressure Contour at 2 Milisecond

7) Pressure Contour at 4 Milisecond

8) Pressure Contour at 8 Milisecond

9) Video Animation of Pressure Contour

10) Video Animation of Velocity Contour

11) Pressure Plot

12) Mass flow rate

13) Velocity Plot

14) Total Cell Count

15) Time taken for Simulation

Conclusion: -

1) From the contour and plot it can be seen that, from the start of deflection of throttle valve, there is an area below the throttle valve have less velocity and it is obstructing the flow very well.

2) From 2 milisecond to 4 milisecond the velocity and pressure are constant which can be seen in plot as well as in contours. The velocity is around 129 m/s and pressure drop of 1.1e5 pascals.

3) The static pressure has been drop in the near vicinity of throttle valve as it has start moving. The total pressure at inlet was around 1.5e5 pascals as stated in the boundary conditions. In the total pressure plot it can be seen that after throttle valve coming to normal position the pressue is increasing and being constant after 8 milisecond to 1.17e5 pascals.

4) From the transient simulation of throttle valve problem, it can be seen that lowering the area of flow cause the velocity to decrease initially and then sudden increase at the outlet due to sudden expansion of flow.