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 arrangement 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 a steady state. Throttling is an Isenthalpic process.

A.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 a number of open edges that were cleaned using a Patch command.

• Creation of Boundaries: In the geometry which is created above, boundaries such as inlet, outlet, outer body and throttle.
• Checking Orientation of Normals: The orientation of Normals was checked to ensure all the normals are pointing inwards. This was done using the Normal Toggle
• 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, Gas Simulation: Default properties were retained.
• Global Transport Parameters:- Default properties retained

3. Simulation Parameters:-

• Run Parameters:- Steady state solver was used. The simulation mode was set to Full Hydrodynamic. The gas flow solver is set to Compressible

- Steady State Monitor:- Minimum no of cycles 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 was set to 0.5.

4. Boundary:

- Inlet:- Boundary flow - Inflow

Inlet Pressure- 150000 Pa

- Outlet- Boundary - Outflow,

- Throttle:-

- Elbow Wall:

4. Initial condition and events: The created geometry was selected as the Volumetric Region,

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

- 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:

MESH VIEW:

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

2) Velocity Contour:

2) Pressure Contour:

• 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:

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 a 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:

CONCLUSION:

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