Flow over a backward facing step at different base mesh sizes
A Gas Flow simulation was setup using air at 300K with an inlet pressure of 101325Pa pressure and 110325 as the outlet pressure on a backward facing step. Therefore there was a pressure difference of 10,000 Pa. Three simulations were done with different base grit/mesh sizes. The velocity and pressure plots were obtained.
The first simulation was done with base mesh size of 1e-3. The total simulation time was 166 seconds.
The velocity contours diagram and the one along with the streamlines.
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972116.png\")
The Velocity magnitude along with the streamlines diagram![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972162.png\")
The Pressure Contours Diagram
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972225.png\")
The graphical plot for all different variables
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972302.png\")
The second simulation was done with base mesh size of 6e-4. The total simulation time was 358 seconds.
The velocity contours diagram and the one along with the streamlines.
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972445.png\")
The Velocity magnitude along with the streamlines diagram
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972427.png\")
The Pressure Contours Diagram
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972479.png\")
The graphical plot for all different variables
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546972520.png\")
The third simulation was done with base mesh size of 4e-4. The total simulation time was 973 seconds.
The velocity contours diagram and the one along with the streamlines.
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546973094.png\")
The Velocity magnitude along with the streamlines diagram
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546973123.png\")
The Pressure Contours Diagram
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546973158.png\")
The graphical plot for all different variables
![\"\"](\"//edxengine-live-courses-files.s3.amazonaws.com/1546973184.png\")
A video animation showing how the simulation progressed and how over time the velocity contour had taken shape until the system reached a steady state.
From the results,
It can be seen that a vortex/recirculating region is created at the begining of the step and a secondary smaller one is created further ahead. There is also an eddy created at the left corner at the begining of the step region. Also a pressure drop is observed when the step begins as the this region as a divergent nozzle due to the increase in area.
The velocity magnitude plots get sharper as the mesh size decreases, however there isn\'t much difference in the plot between the base mesh size 6e-4 and 4e-4. But 6e-4 takes much longer computational time in comparison.
Therefore i suggest 1.5e-4 as the most appropriate mesh size.