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

Aim: The aim of the project is to simulate the flow through a throttle body. The objective is to understand the development of the flow with the aid of different plots.

Theory:

The throttle valve arrangment which is the subject of this analysis is frequently used in automobiles to regulate the air fuel mixture in the combustion engine. Butterfly valves are the most commonly used valves . In this analysis we would be examining the results under the assumption of steady state.

Throttling is an Isenthalpic process.

Case Setup:-

1. Geometry Creation:- The geometry that was used for the analysis is shown below. An STL file was imported into CONVERGE. It comprised of a number of open edges that were cleaned using a Patch command.

1. Creation of Boundaries: In the geometry which is created above, boundaries such as inlet, outlet , outer body and throttle.

1. Checking Orientation of Normals:Orientation of Normals were checked to ensure all the normals are pointing inwards. This was done using the Normal Toggle
2. Finally a Diagnosis check was run to ensure no errors in the geometry.

B Case Setup

1. Application Type:- This was set to Time based

2.Materials:- This was set to Air

1. i) Gas Simulation: Default properties were retained
2. ii) Global Transposrt Parameters:- Default properties retained
3. Simulation Parameters

- Run Parameters:- Steady state solver was used. Simulation mode was set to Full Hydrodynamic. Gas Flow solver set to Compressible

- Steady State Monitor:- Minimum no of cycles for to be executed for Steady state solver -500

Monitor Start Delay, cyc :- 8000

Sample size cyc :- 1000

- Simulation Time Parameters:- The parameters were set as displayed below. Max CFL limit set to 1.0

- Solver Parameters:- A Pressure based PISO solver was used, Maximum Convection CFL limit set to 0.5.

4. Boundary

- Inlet:- Boundary flow - Inflow

Inlet Pressure- 150000 Pa

- Outlet- Boundary - Outflow

- Throttle:-

- Outer

4. Initial condition and events

The created geometry was selected as the Volumetric Region

5. Physical Models:- Default retained
6. Turbulence Modelling:- RNG-kepsilon turbulence model is used
7. Grid Control:- A Grid size of 0.002 is entered in dx,dy and dz direction

Fixed Embedding was also enabled. This was done to capture the flow around the throttle valve with greater precision.

7. Output/Post Processing:- The variables that we intend to see during post processing are selected. In this case Density, Pressure , Temperature and Velocity were selected.

After setting the above, the input files were exported to a directory

In order to execute the simulation, the directory in which these input files were stored was accessed in Cygwin and the following command was typed "mpiexec.exe -n 4 converge.exe"

After the Simulation was executed, the results were converted into a form which would be compatible with Paraview. This was done using the post_convert.exe command.

Results:-

Surface with Mesh

1) A Slice cut out with normal in Z direction is given below

2) Velocity Contour

2) Pressure Contour

3) Density Contour

4) Velocity Array

It can be seen that the throttle valve does not seal completely and flow occurs along the sides.

Pressure drop across the throttle

From the above plots it is observed that no significant pressure drop is encountered across the throttle.

Plots.

i) Mass Flow Rate

ii) Average Velocities

i

iii) Total Pressure

From the above plot it is seen that while the inlet pressure is constant at 150000 Pa, the outlet Pressure reaches a value of little below 120,000 Pa after 2000 cycles.

From the above plots we observe that the values for mass flow rate, average velocity and total pressure attain convergence after 2000 cycles.

iv) Cell count

Cell count remains a constant at 13000 throughout the computational cycle

Conclusion

It is observed that the solution reaches a steady state at 2000 cycles. No significant pressure drop is encountered across throttle