Converge CFD

Flow over backward facing step using Converge CFD

OBJECTIVE-Simulate the flow over backward facing step

Case-1:  Grid size- dx=2e-3, dy=2e-3, dz=2e-3

Case-2: Grid size- dx=1.5e-3, dy=1.5e-3, dz=1.5e-3

Case-3: Grid size- dx=1e-3, dy=1e-3, dz=1e-3

Geometry-A geometry backward facing step was created.

Setup-

Applications-

-General flow

Materials-

-Air

Simulation Parameters:

-Pressure based steady state solver

-Start time-0, End time-15000 cycle

-Intial time step=minimum time step=1e-6 s

-Maximum time step=1 s

Boundary conditions-

-Inlet- INFLOW-Total pressure-110325 pa

-Outlet- OUTFLOW-Total pressure-101325 pa

-Top & bottom- WALL

-Front- 2D

-Back – 2D

Regions & Initialization:

Boundaries are assigned to region

Temperature and pressure set to 300K and 101325pa

Species-Air

Grid control: 2mm,1.5mm,1.2mm respectively

Fixed Embedding:Top and bottom-scale-1 ,layers-1

Case-1:  Grid size- dx=2e-3, dy=2e-3, dz=2e-3

Mesh-

Total cell count:

We can see from the below graph that the total cell count is 2000.

Graphs to check the convergence of the solution from line plotting module:

The below graphs contain the mass flow rate, velocity , pressure at inlet and outlet respectively.We can see from these graph that the solution has attained a constant value after around 3000 cycles in all the plots.So we can conclude that the solution has reached a steady state.

Mass flow rate at inlet:

Mass flow rate at outlet:

Pressure plot at inlet and outlet:

Velocity plot at inlet and outlet:

Results-

Velocity Contour:

Pressure Contour:

Velocity vector near recirculation region:

The wake region can be seen from the below vector plot.We can see the recirculation region just behind the step.

Case-2: Grid size- dx=1.5e-3, dy=1.5e-3, dz=1.5e-3

Mesh-

Total cell count:

Mass flow rate at inlet:

The below graphs contain the mass flow rate, velocity , pressure at inlet and outlet respectively.We can see from these graph that the solution has attained a constant value after around 5000 cycles in all the plots.So we can conclude that the solution has reached a steady state.

Mass flow rate at outlet:

Pressure plot at inlet and outlet:

Velocity plot at inlet and outlet:

Results-

Velocity Contour:

Pressure Contour:

Velocity vector near recirculation region:

The wake region can be seen from the below vector plot.We can see the recirculation region just behind the step. 

Case-3: Grid size- dx=1e-3, dy=1e-3, dz=1e-3

Mesh-

Total cell count:

Mass flow rate at inlet:

The below graphs contain the mass flow rate, velocity , pressure at inlet and outlet respectively.We can see from these graph that the solution has attained a constant value after around 5000 cycles in all the plots.So we can conclude that the solution has reached a steady state.

Mass flow rate at outlet:

Pressure plot at inlet and outlet:

Velocity plot at inlet and outlet:

Results-

Velocity Contour

Pressure Contour

 

Velocity vector near recirculation region:

The wake region can be seen from the below vector plot.We can see the recirculation region just behind the step.

Animation:

 

 

Flow Sepatation:

-This is taking place at the back of the step where the area is increased abruptly.

-Due to positive pressure gradient created at this zone,the flow start moving backward.

-As a result the flow separtes and a recirculation region is formed due to flow in opposite direction.This is also called wake region.

Conclusion:

1. The simulation for three different grid size were run.

2. With decrease in grid size the contours became smoother and more accurate results were found.

3. Embedding helped to capture the physics nears walls more prominently.

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