Week 1: Channel flow simulation using CONVERGE CFD

As Converge-studio, Cygwin, and Paraview are installed in the system, So we begin with geometry design, and in this we create a box formation and check its normals, which must be pointed in the direction of the flow. After that, a diagnosis is done to check for any kind of geometrical error. After veryfing it, the case setup is set as per the given inputs and boundary conditions. In this case, all the basic parameters are selected with specific values, and all these values are setup together as input files for the model. At last, export the input files into the folder.

The simulation follows, which can be converged by using the Cygwin interface, which is required for giving the command to the software.In Cygwin, first we go to the directory where the input files are present and then command them for simulation. This simulation can be done automatically at the back  end, and the output files are generated in the same folder as the results of the simulation.

Then those output files have to be exported in Paraview to see the results in the different interfaces and also in their plots in the Converge Studio. For importing the output files in Paraview, first we need to convert the data into a ".vtm file," which is done in the "Post-Processing 3-D" option in Converge-Studio. Then all the 3D and 2-D analyses of the results are analysed separately. The rest of the plots can be seen in Converge-studio itself, specifically under the "line-plotting option."

By doing so, I was able to obtain all of the required results for this particular challenge and take screenshots of them.The CFD analysis of this problem is done three times for three different mesh sizes, and the results are attached in a word file. Kindly find it below.

Detailed explanations about the plots:

1. The cell count plot shows that as the mesh size decreases, the number of total cell counts increases, indicating that decreasing the mesh size increased the number of cells.We can also understand that by the same token, in the fixed volume, if the mesh size decreases, that means the per-mesh volume also reduces. So to equalise the sum-total volume of meshes with the total volume of the geometry, more cells are required, which increases the cell count. Here, the total cell count is near about 25000, 46000, and 100000, respectively, for cases 1, 2, and 3.

2. The mass flow rate plots appear to be very unstable at first touch, but as the flow cycled on, convergence took effect.After achieving the convergence shown in the graph, we observe that the mass of the flow that enters the geometry from the inlet per unit of time is equal to the mass of the flow that exits from the outlet. But due to the sign conventions, the input and output flows are represented, respectively, as positive and negative values for comparison.

3. The velocity plots also look unstable in the starting phase, but as the flow loops after a few circulations, the flow achieves its convergence as in the case of flow rate. After achieving the convergence shown in the graph, we observe that the initial velocity is nearly equal to the velocity at the outlet. But due to the sign conventions, the input and output flows are represented respectively as positive and negative values for differentiation. But along with this, if the simulated results of the Paraview file are analysed, the velocity varies as the flow goes away from the wall. This is due to the no-slip criteria that we selected for simulation. The overall velocity curve follows a parabolic curve in the direction of the flow, with the layer of the flow along the wall being very close to static/rest and the flow-velocity increases relatively fvery high in the middle. As the mash size decreases, the local variation in the velocity flow becomes more apparent.

4. The pressure graphs look unstable in the starting phase, but as the flow goes on, after some time, the flow achieves its convergence, as in the case of flow rate. The initial unstable pressure plot is very similar to the velocity plot. The pressure at the inlet and outlet remains the same throughout the time, but at different magnitudes because of the different initial conditions that are given to both ends in the case setup for making fluid flow inside the channel. In addition, a constant change is observed from the inlet to the outlet in the simulated results, in the direction of the flow, in the Paraview file. As the mash size decreases, the local variation in the velocity flow becomes more fine and clear.

Thankyou

Animation link: https://youtu.be/8VJX_w25Nl0 

Anubhav