Flow over a backward facing step simulation using CONVERGE CFD
In this project flow over a backward facing step is simulated. Flow over backward facing step simulation is a popular benchmark used to verify turbulence models of CFD setups. It is also used in studying of flow seperation.
Mesh sizes used are as follows:
Mesh size 1: 2.0e-3m
Mesh size 2: 1.5e-3m
Mesh size 3: 1.2e-3m
Boundary conditions are as follows:
Inlet: 110325Pa
Outlet: 101325Pa
Top and bottom wall: Law of the wall condition is used.
The working fluid for the simulation is taken as air. The turbulence model used here is the RNG k-`epsilon`model. The flow is simulated using steady state pressure based solver and the simulation is run for 30,000 cycles for all the three cases. For all the pressure plots below the x-axis is height of the channel (m) and y-axis is Pressure (Pa) and for all the velocity plots below the x-axis is height of the channel (m) and y-axis is the velocity (m/s).
The 2D view of model used for the simulation:
Mesh size 1:
Results for mesh size 1:
Pressure contour:
Pressure plot 0.021m before step:
Pressure plot 0.021m after step:
Velocity contour:
Velocity glyph arrows:
Velocity plot 0.021m before step:
Velocity plot 0.021m after step:
Mass flow rate at inlet and outlet:
Mesh size 2:
Results for mesh size 2:
Pressure contour:
Pressure plot 0.021m before step:
Pressure plot 0.021m after step:
Velocity contour:
Velocity glyph arrows:
Velocity plot 0.021m before step:
Velocity plot 0.021m after step:
Mass flow rate at inlet and outlet:
Mesh size 3:
Results for mesh size 3:
Pressure contour:
Pressure plot 0.021m before step:
Pressure plot 0.021m after step:
Velocity contour:
Velocity glyph arrows:
Velocity plot 0.021m before step:
Velocity plot 0.021m after step:
Mass flow rate at inlet and outlet:
Comparison of total cells count for the three mesh sizes:
Velocity contour animation:
From the simulation it is observed that the flow seperates after crossing the step, it is because after passing the step, the flow gets recirculated from high pressure areas to fill the low pressure areas of the channel this causes adverse pressure gradient in the lower part of the flow as it flows through the expanded channel this causes the flow to seperate. The recirculation region can be clearly seen from the velocity glyph arrows images.