Week 1: Channel flow simulation using CONVERGE CFD

Aim: Channel flow simulation using CONVERGE CFD with different Grid Sizes. Plot contours of velocity, pressure and mass flow. And Create animation. Discuss the results.

Introduction and Theory:

1. As Suggested, Channel flow simulation has been set up in CONVERGE.
2. In this channel simulation, Air is flowing through the channel from one to another end.
3. This channel is a square box. One end is maintained just above atmospheric pressure and another at atmospheric pressure.
4. Having this difference in pressure makes airflow from a high-pressure point to a low-pressure point.
5. During this simulation, the temperature is considered as room temperature. 300K

   This setup had the same inlet pressure and initial pressure.

   

Case Setup:

1. In converge, we are selecting a Time-based application for this project.
2. For materials, we are selecting a predefined mixture as Air which has Oxygen and nitrogen as species of this mixture.
3. In this project, turbulence models are not included. This project was running for the maximum limit of 15000 cycles and after every 100 cycles restart files and result snapshot was recorded.
4. The solver parameters were defaulted to Navier stokes equation-based PISO solver.
5. This particular project is an example of steady-state simulation.
6. The channel is assigned different boundary conditions:
   1. inlet (High pressure point)
   2. outlet (low-pressure point)
   3. Walls (top and bottom)
   4. 2D sliced walls (front and back)
7. After setting up the grid size, variables for post-processing were selected. (velocity, mass flow, pressure, density, temperature)
8. After exporting input files, using CYGWIN (command prompt) was used to simulate the project setup.
9. Output files were later converted using CONVERGE studio for post-processing in ParaView.

• After the setup, different cases were post-processed based on the base mesh(grid) size. Results are as following in this table:

Mesh Size 1 dx = 2e-4m, dy = 2e-4m, dz = 2e-4m	Mesh Size 2 dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m	Mesh Size 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

Summary of Comparative results:

1. Total cell counts increase as base grid size decreases from 2e-4 to 1e-4. Due to this reason, the computation time increases. Also, the computation is nothing but approximation with an initial guess and later converging. This means local mesh specification is necessary rather than global mesh edit. Cell counts are increasing from to 25000 cells to 100,000 cells.

2. The velocity and pressure contours are more refined as the base grid size is decreased.

3. The average velocity plot, total/static pressure plot, average mass flow plot for inlet boundary is decreasing and for the outlet is increasing. This is because to attain the equilibrium between inlet and outlet boundary conditions.

4. In the ParaView, a plot over the line can be seen for Velocity in x-direction of air molecules against point on Y-axis. Due to adhesion and no-slip condition between air molecules and the wall of the box, we can see a gradient curve of the velocity profile.

• Here is the animation of the flow where you can see: velocity contour, pressure contour, mass flow, the mass flow of N2.

• Here is the glyph plot to show the direction of the flow-through channel viz. left to right (+x axis).

Conclusion: Channel simulation with 3 different mesh configurations have been analyzed and plots, contours have been obtained using ParaView.