Flow Over a Backward Facing Step

Objective:

To simulate the flow over a Backward Facing Step in Paraview by preparing the Case Setup in Converge Studio using three different base mesh sizes.

Theory:

The Backward Facing Step problem holds significant importance in CFD as it is used as a testing base for running codes of different problems especially in turbulence modelling,as there is numerous data available for it.

Procedure:

1. Create the geometry according to the required dimensions in Converge Studio using the Create option. Under that ,select the Triangles option and set up the geometry using From Three Vertices option.
2. Flag and designate the boundary regions using the Boundary option.
3. Create the Case Setup with the required variables.
4. Enter the three different mesh sizes 2e-4m,1.5e-4m & 1.2e-4m in the Base Grid option (use e-3 if e-4 is too demanding for the computer to process).
5. Check for any Case Setup issues by using the Validate All option.
6. Export the input files to a designated folder and run the simulation using Cygwin.
7. Convert the output files obtained from the simulation in Paraview.
8. Simulate the flow for pressure and velocity and plot the graphs in Paraview.

Result:

By simulating the flow of this problem, the change in pressure,velocity and other variables can be observed by the change in geometry.The output results and findings are shown below.

Fig 1.1: The outputs obtained from the simulation

Fig 1.2: Velocity Magnitude

We can observe the velocity variation of the air in Fig:1.2. The velocity is at its highest (shown in red) when the area is less or when the pressure is low. There is a flow separation when the area increases and due to this the velocity decreases. There is also vacuum created (shown in blue) when the area increases.

Fig 1.3: Pressure Variation

The pressure being viewed here is static pressure.It is seen that the pressure is low when the area is less and it starts increasing when the area increases. The pressure also appears to be a little disturbed at the separation point because of the sudden change in geometry.

Fig 1.4: Vector Flow Direction

The direction of flow of air is shown by the vectors in Fig:1.4. The vectors tend to swirl and flow in the reverse direction when the geometry changes. This is because there is a flow separation due to a sudden increasse in the area.

Fig 1.5: Velocity in X axis

Fig 1.6: Velocity in Y axis

Fig 1.7: Velocity in Z axis

Fig 1.8: Velocity Magnitude

Fig 1.9: Pressure Graph