Week 1: Channel flow simulation using CONVERGE CFD

AIM: To perform a channel flow simulation using Converge and post-process the result in Para view.

OBJECTIVE:

• To run 3 simulations and compare the results between all the 3 simulations.
• The impact of three different mesh sizes will be studied
• Understand flow development with the aid of plots for velocity, pressure and mass flow rate.

A.CASE SETUP:

A. Geometry Creation:

• Creating the Geometry:- A rectangular channel is created by selecting "Box" under "Create"

• dx, dy and dz values are entered to create a channel as shown below,

• Creation of Boundaries: In the geometry which is created above, boundaries such as inflow, outflow, top and bottom walls, and front and back faces are labelled.

• 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:

• Application Type:- This was set to Time based,

• Materials:- This was set to Air,

i) Gas Simulation: Default properties were retained,

ii) Global Transport Parameters:- Default properties retained,

• 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 denisty-based PISO solver was used, Maximum Convection CFL limit was set to 0.8.

• Boundary: - Inlet:- Boundary flow - Inflow

• Inlet Pressure- 100001 Pa,

• Outlet- Boundary - Outflow,

• Top and Bottom Walls:- Stationary wall with Fixed surface movement used,

• Front and Back faces set to Two D,

• Initial condition and events:

  The created geometry was selected as the Volumetric Region,

• Physical Models:- Default retained,

• Grid Control:- Base Grid. Here the size of the mesh for the three cases is entered,

• 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.

• Also, the frequency of generation of output files was set below,

• Final validation is done, it seems to be no error in the case setup,

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

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:

1) Case-1 ( dx=dy-dz=2e-4):

• View of the Mesh:

• Velocity Contour:

• Pressure Contour:

Plots for :

• Velocity (After approximately 15000 cycles)

• Pressure:

• Mass Flow Rate:

• Cell Count:

• Velocity Animation:

2. Case-2 (dx=dy=dz= 1.5 e-4):

• View of the Mesh:

• Velocity Contour:

• Pressure Contour:

Plots for :

• Velocity (After approximately 15000 cycles)

• Pressure:

• Mass Flow Rate:

• Cell Count:

• Velocity Animation:

3. Case-3 (dx=dy=dz=1.2 e-4):

• View of the Mesh:

• Velocity Contour:

• Pressure Contour:

Plots for :

• Velocity (After approximately 15000 cycles)

• Pressure:

• Mass Flow Rate:

• Cell Count:

• Velocity Animation:

CONCLUSION:

• It is observed that velocity in the initial case is highest but as the mesh is coarse it is generally not preferred to be accurate. In the next two cases, it was calculated more accurately.
• The pressure obtained in all the cases remains constant. This is because both the inlet and outlet are provided with constrained boundary conditions.
• The mass Flow Rate at the outlets for the refined cases is almost the same. When both inlets and outlets are compared, we can observe a positive flow and a negative flow.
• Hence, as the grid size increases the results obtained are much clear and more accurate.
• The channel flow simulation using Converge CFD is performed. With different mesh sizes, accurate results are obtained.
• Various plots, contours, profiles, and animations are generated in order to get a clear understanding of how the flow is inside a channel with the help of Converge CFD software.