Channel flow simulation using Converge CFD

Introduction :

In this project, a flow through a channel has been set up using Converge 3.0 software from Convergent science. Converge software is a high performance computing CFD package used in industry with applications like IC engines, Fuel injectors and sprays, Exhaust after treatment etc. 

The Solver is ran using a command line interface program called Cygwin and post processed in Paraview.  

The case is run for 3 different meshes and multiple explanatory plots have been created to explain the Fluid flow.

Geometry Creation in Converge Studio : 

Shape - Box : 

Center : Xdir - 0.05 m 

Size of box : Xdir - 0.1m Ydir - 0.01m Zdir - 0.01m

The geometry simulated is going to be in 2D boundary condition, the image below represents the front side to visualize. 

Meshing : 

The Case is solved for 3 different Mesh sizes, They are mentioned as below 

Case 1 : 

This is the baseline mesh at 2.5e-4 m size elements. 

Total Cell count for Case 1: 

Xdir : 0.1/2.5e-4 = 400 cells ; Ydir : 0.01/2e-4 = 40 cells

Total cell for 2D , x*y = 16000 cells

Case 2 : 

This is slightly refined case with 2e-4 m sized elements.

Total Cell count for Case 2: 

25000 cells

Case 3 :  

This is a highly refined case with 1.5e-4 m sized elements with almost double the total elements than previous one. 

Total Cell count for Case 3 : 

44443 cells

Case Setup : 

1. Application type : Time Based

2. Material : Air mixture ( Gas simulation) 

3. Gas Species : 02 , N2 .

4. Solver : Steady state solver , Fully Hydrodynamic. 

5. Gas flow solver : Compressible.

6. Misc : Momentum , Energy on 

7. Steady state monitor :  On. - min cycles : 500

8. Monitor Variables : Avg Velocity at Outlet

9. Simulation Time parameters : 

i. Start 0 cyc

ii. End : 15000 cyc. 

iii. Initial Time-step : 1e-9s

iv. minimum Time-step  1e-9s

v. Max time-step 1s.

10. Solver scheme : Piso algorithm 

11 Pressure : No preconditioner .

12. Boundary Conditions : 

i. Inlet : Inflow ; Pressure : 100001 Pa ; Temp : 300k ; Species : O2 , N2.

ii. Outlet : Outflow ; Pressure : 100000 Pa ; Temp : 300k; Species : O2, N2. 

iii. Top-bottom-walls : Stationary : Fixed : No-slip

iv. Front : 2D

v. Back : 2D

13. Regions & Initialization : 

14 Volumetric Region created : Speciies : O2,N2 .

15. Output Files : Time interval for writing 3D output data files : 100 cyc.

16. Max restart files saved : 3 

 Solution & Post Processing : 

The Input files are exported from converge, then the solver is executed using cygwin command line interface. After which the output files generated are again ran using cygwin to convert them for post processing software Paraview. 

The solution reaches convergence before 15000 cycles are completed and the solution is terminated when the tolerance is reached. For each case this value is different. 

Case 1. 

The simulation run time for case 1 is 593.4 seconds

Velocity Contour : 

The blue color indicates least velocity whereas red indicates Highest velocity.

Velocity plot : 

The velocity profile is parabolic as we can see at x = 0.08 m. The step formation observed is due the mesh size. As seen from the contour on the left, the wall region has high viscosity and at the wall its no slip , hence we can see the velocity being nearest 0 and thus increasing as it moves further away from the wall. 

Pressure Contour : 

Pressure Plot :

The Case was set up for the fluid to flow due pressure difference of 1 pa , and that is what we observe in the plot below, at inlet the pressure is 1 pa greater and as proceed to the outlet the pressure reduces to 100,000 pa. 

Mass flow rate : 

For the mass flow rate observed , the bound id 1 represents inlet and similarly 2 represents outlet. We can see the mass flow rate linearly increases and then reaches a convergence at ~5500 cycles. This satisfies the mass conservation equation at inlet & outlet. 

Case 2. 

The simulation run time for case 1 is 1190.93 seconds

Simulation took longer time due to Finer mesh size

Velocity Contour :

Velocity plot : 

We can observe the slight changes in velocity as the mesh was made finer from the contour.  Also due to finer mesh size the plot looks smoother.

Pressure Contour : 

Pressure Plot :

The plot looks smoother due to the finer mesh size.

Mass flow rate : 

Case 3. 

The simulation run time for case 1 is 3053.128 seconds

Velocity Contour : 

Velocity plot : 

theres Slight change in velocity due to finer mesh size. We can see the parabolic curve properly forming. Very smoother looking plot. 

Pressure Contour : 

Pressure Plot :

The plot looks extremely smoother. 

Mass flow rate : 

Mass conservation can be observed. 

 Animation : 

The fluid flows from left side inlet to outlet right side, we observe the velocity slowly increasing as number of cycles are iterated, it is observed the wall regions the fluid adheres due to no slip condition and velocity is nearly 0 there and it forms a parabolic curve following hydrodynamic eqns. 

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