Channel flow simulation using CONVERGE CFD
Aim- To study the flow characteristics of fluid passing through a square channel and comparing the results for different mesh sizes.
Governing equation- The equation used to solve this case is Navier-Stokes Unsteady equations. It comprises of 5 equations continuity, x-momentum, y-momentum, z-momentum, and energy equation. But for this case, the energy equation is not used since there is no gain or loss of energy and the temperature is constant throughout the simulation.
Objective- The objective of this problem is to simulate fluid flow passing through a square channel of dimensions x=0.1m, y=0.01m, z=0.01m. 3 base mesh is created with every mesh having a smaller mesh size than the previous case and pressure, velocity contours plot are compared so that a suitable mesh can be selected which gives accurate results.
Description- First the geometry to be simulated is created in Converge Studio and then the geometry is checked for any errors. The geometry is grouped into faces so that respective boundary conditions can be assigned and then the case setup is done. For this project, we will be running a steady-state simulation with a number of cycles 10,000 and end time 1s. It is a laminar flow simulation since it is simple fluid flow passing through a square channel and hence no turbulence model is selected. For case1 the mesh size applied is 2e-4m in all directions and then becomes finer for further cases. In this project, the whole geometry is refined and no specific region is refined.
Geometry-The dimensions of the square channel are x=0.1m, y=0.01m, z=0.01m.
Material-Air
Boundary Condition-Inlet: Pressure inflow of 100001 Pa
Outlet: Pressure outflow of 1e+5 Pa
Top-bottom: Fixed wall
Sidewalls: 2D
Initial Condition- Pressure:1e+5 Pa and temperature:300K
Mesh- a) Mesh size:2e-4m
b) Mesh size:1.5e-4m
c) Mesh size:1e-4m
Results-For Mesh size 2e-4m
Pressure contour
The pressure is high at the inlet and low at the outlet which means that the flow takes place from left to right.
Velocity contour
The velocity at the walls is almost zero because of the no-slip condition at the wall which gives rise to viscous forces and it increases at the center of the channel since boundary layer effect is negligible.
Velocity plot
This is actually a graphical representation of the velocity contour at a specific section of the channel. On the x-axis, we have channel height and on the y-axis we velocity.
Link to the velocity animation:https://youtu.be/YfBwggdZifM
For Mesh size 1.5e-4m
Pressure contour
The pressure is high at the inlet and low at the outlet which means that the flow takes place from left to right.
Velocity contour
The velocity at the walls is almost zero because of the no-slip condition at the wall which gives rise to viscous forces and it increases at the center of the channel since boundary layer effect is negligible.
Velocity plot
This is actually a graphical representation of the velocity contour at a specific section of the channel. On the x-axis, we have channel height and on the y-axis we velocity.
Link to the velocity animation:https://youtu.be/gDCGgcDcJwg
For Mesh size 1e-4m
Pressure contour
The pressure is high at the inlet and low at the outlet which means that the flow takes place from left to right.
Velocity contour
The velocity at the walls is almost zero because of the no-slip condition at the wall which gives rise to viscous forces and it increases at the center of the channel since boundary layer effect is negligible.
Velocity plot
This is actually a graphical representation of the velocity contour at a specific section of the channel. On the x-axis, we have channel height and on the y-axis we velocity.
Link to the velocity animation:https://youtu.be/3Zj7kk9aXUs
Conclusion
From the pressure plots, we can see that the pressure is low at outlet than the inlet which means that flow is taking place from left to right. This also ensures that there is no backflow or reverse flow taking place at the outlet.
The velocity at the walls is ~0 because of boundary layer effect and it increases in the center to attain free stream velocity. This phenomenon is also evident from the velocity plot which shows the variation of velocity w.r.t the channel height.
As the mesh size reduces the cell count increase but this also helps in increasing the accuracy of the simulation. This can be seen in the case3 velocity plot where the steps in the graph are small and it's smoother to achieve parabolic characteristics.