Week 3: Flow over a backward facing step

Objective: Flow Over a Backward Facing Step

We have Simulate the flow over backward facing step in 3 different grid size cases

• Case 1 grid size (dx=dy=dz=2e-3)
• Case 2 grid size (dx=dy=dz=1.5e-3)
• case 3 grid size (dx=dy=dz=1.2e-3)

Case setup of geometry in converge

Case Setup:

Application Type: Time base or General flow

Material: Air and Species (N2=77% & O2=23%)

Simulation Parameter:

1. Run parameter: Solver (steady-state solver)
2. Simulation Mode:(Fully-hydrodynamic)
3. Gas flow solver: (Compressible)
4. Solver Time Parameter: (start time = 0 cyc, End time = 15000 cyc)
5. Initial Time step: 1e-9 sec
6. Minimum time step:1e-9 sec
7. Max convection CFL: 1

Boundary Condition

1. Inlet (Pressure = 110325 pa & Tem = 300k)
2. Outlet (Pressure = 101325 pa & temp = 300k)
3. Front & Back = 2D Wall
4. Top & Bottom Wall = No Slip Wall Condition

Initial Conditions

1. Region and Initialization
2. Species Air (N2=77% & O2=23%)

Case 1: grid size (dx=dy=dz=2e-3)

Mesh:

Total Cell Count: 1943

Mass Flow rate at Inlet:

Mass Flow rate at Outlet:

Velocity profile at inlet:

Velocity Profile at outlet:

Pressure at inlet:

Pressure at outlet:

Vertex Vector orientation:

Velocity Contour:

Pressure Contour:

Result:

Velocity Profile

Prssure Drop down:

• Case 2 grid size (dx=dy=dz=1.5e-3)

Mesh:

Total Cell Count: 3004

Mass Flow rate at Inlet:

Mass flow rate at Outlet:

Velocity Profile at Inlet:

Velocity Profile at Outlet:

Pressure at Inlet:

Pressure at Outlet:

Vertex of Vector Orientation:

Velocity Contour:

Pressure Contour:

Result :

Velocity Profile:

Pressure dropout:

• case 3 grid size (dx=dy=dz=1.2e-3)

Mesh :

Total Cell Count : 4800

Mass Flow Rate at Inlet:

Mass Flow rate at Outlet:

Velocity Profile at Inlet :

Velocity Profile at Outlet:

Pressure Profile at Inlet:

Pressure profile at Outlet:

Vertex of Vector Orientation:

Velocity contour:

Pressure Contour:

Result:

Velocity Profile:

Pressure drop down profile:

Animation Film Velocity :

Animation Film of pressure:

Conclusion:

• The air flow from inlet is higher than outlet this because the backward facing step which change the geometry of fluid domain.
• Deu to backward facing step pressure drop near the step this cause the some fluid particle flow in reverse direction. Which creates Vertices.
• Which the increase the no of cell the the solution becomes more accurate.
• The Increase the grid size of cell increase the no of cell and solution becomes more and more accurate.