Steady State Simulations to Compare the mixing effectiveness in Tee Geometry Using Ansys Fluent

AIM: To setup steady state simulations to compare the mixing effectiveness in Tee geometry. 

• Case 1 
  • Short mixing tee with hot inlet velocity of 3m/s
  • Momentum ratio of 2
• Case 2 
  • Long mixing tee with hot inlet velocity of 3m/s
  • Momentum ratio of 2
• Case 3
  • Short mixing with hot inlet velocity of 3 m/s
  • Momentum ration of 4

where Momentum ratio = velocity at cold inlet / velocity at hot inlet

PROCEDURE:

1. Geometry Importing and Volume Extraction:

• First open Ansys Workbench and click on Fluid Flow (Fluent) and drag it to the GUI screen.
• Then double click on geometry to navigate to Ansys Spaceclaim. Here open the required file.
• The short mixing tee geometry will look as below:

The long mixing tee geometry is as follows:

• Since the analysis is only done for the wet volume hence only that is volume is extracted. For this select volume extract -> select edges and select the edges where fluid has contact with the body. The geometry with dimensions will look as below:

Short tee model:

Long tee model:

• Now after the wet volume is extracted the dry volume which is the shell is not to be included for the simulation. For which Suppress for Physics option is selected for the shell.

2. Meshing:

• Now the geometry is meshed using the mesh option available in the workbench. Here tetrahedral mesh type is used.
• The mesh size is 4mm i.e. 4e-003 m and the meshed model is as below:

meshed model for short tee geometry:

meshed model for long tee geometry:

• The faces of the geometry are given their respctive names as below:

3. Solving:

• Now the meshed component is solved using ansys fluent for which double click on setup option in workbech GUI to navigate to Fluent.
• Here the boundary conditions are set and solutions are obtained.

CASE -1 :

           INLET-X:

           temperature = 25 C , velocity = 3m/s

           INLET-Y:

           temperature = 10 C , velocity = 6m/s

Residual plot:

It is seen that after 250 iterations the plot pattern is repeating . Hence the convergence iteration is 250.

Temperature plot:

Standard Deviation plot:

CASE - 2:

           INLET-X:

           temperature = 25 C , velocity = 3m/s

           INLET-Y:

           temperature = 10 C , velocity = 6m/s

Residual plot:

Here the solution is converging at 180 iteration.

Temperature plot:

Standard Deviation plot:

CASE -3 :

           INLET-X:

           temperature = 25 C , velocity = 3m/s

           INLET-Y:

           temperature = 10 C , velocity = 12m/s

Residual plot:

Here as mentioned in the console and also from the plot the solution is converging at 137 iteration.

Temperature plot:

Standard Deviation plot:

4. Post processing:

• Now after obtaining the solutions the model is post processed to see the results. For which double click on results in the workbench GUI to navigate to CFD post.
• For the given geometry a plane is created on which the simulation results can be observed and they are as follows:

CASE -1 :

Temperature plot:

Velocity plot:

CASE -2 :

Temperature plot:

Velocity plot:

CASE -3 :

Temperature plot:

Velocity plot:

TABLE:

CONCLUSION:

From the above discussed results we can infer that the best mixing effectiveness is achieved in case-3 and this can be seen in the respective temperature contour plot. Here due to the high velocity of cold fluid, a good amount of turbulence is generated which can be seen in the pressure contour plot and thus helping the cold air to penetrate further into the moving fluid resulting in good mixing efficiency.

Also from the table we see that the standard deviation in the 3rd case is very low when compared to the other two cases. Apart from this, convergence is also achieved at a faster rate. Though being a short tee geometry it is being successful in reaching low temperatures. All these factors make this tee geometry the most effective one.