2. Solving 2D Problems

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In this tutorial we will discuss about the 2D problems which involve defining boundary condition and solving them. Iam going to create the nozzle with the air velocity inlet (ideal) and pressure outlet. Improving mesh obtain good result.

  1. Step 1: Starter...

    Open up your ansys workbench and drag the CFD Fluent onto the workspace or double click on it. I name this as Tutorial 1 or can be left default.




    Note: Make sure to open CFD Fluent not CFX.

    Mostly CFX is ignored because it is not supported with 2D models but good for mesh moving methods (will be thought later).

  2. Step 2: Geometry

    Double click on geometry. Iam using design modeler for latest version ANSYS by default opens up space claim. But can be changed to open in design modeler.


    After double clicking or to be on safe side right click and select edit geometry in design modeler. Make sure about geometry units from units tab set as millimeter (in this instance). A home screen of design modeler looks like this:



    Now from left side select any one plane (in this case XY Plane) and then look at face/plane/sketch and the select sketching



    Note: You have to clear with sketching or any model can be imported ( will be thought later)


    You can use line or basic shape from draw tab. Trim or erase from modify tab. Mark dimensions and control values from dimension tab. And constrain tab for adding constrains.

    Now draw a 2D shape of nozzle which look like:


    Note: This might be difficult for first time user but try those, it would be really easy for well versed.

    Now exit the sketching by clicking the modeling next to sketching. Then select concept -> surface from sketch -> select any one line from sketch and hit apply and press generate or F5.



    Resultant surface:





  3. Step 3: Mesh

    Now close the design modeler and on the workbench you must see the green check mark next to geometry and double click on mesh. Wait until the model is loaded. There are only two steps that must be carried.


    Naming selection:

    Make sure to name the edges or faces. This is important.



    Meshing:


    Meshing is a continuous process which involve the clarity of model and solution. After a continuous iteration my model mesh values are below:


    In the above I used face meshing (select one face of the 2D model) because structured mesh cause good result and reduce time of meshing. With each mesh elements of 0.35 mm took me 10 seconds only. After finalizing your mesh click on update to update your mesh onto mesh on workbench. After update close this window and you must see the another check mark next to mesh.




  4. Step 4: Setup and Solution

    These both are controlled in under a same window. This is the important step in CFD Fluent. All terms related to CFD like viscosity, ideal gas, and other constants.


    Now double click on setup, this opens a fluent launcher. You can check the double precision and select the number of cores to be used for solving and hit ok.


    This opens up a window and wait till the model gets loaded and stays still.



    Our model is gonna be steady state with no gravity included with all set, double click on models (left side of page) we are going to change viscous to k-epsilon.



    You must have knowledge with these model types and when should be used. As this is example I use k-epsilon and hit ok.


    Next double click on material ans select air, change the constant density as ideal and hit change/create and press close.



    In cell zone condition make sure the surface body is fluid.


    Double click on boundary condition and select inlet (double click) make sure to check the velocity inlet and enter the velocity value.



    On outlet check the pressure-outlet and gauge pressure is zero. Hit ok.



    Almost everything has been done.

    Now time to initialize the solution. Double click on initialization and choose hybrid initialization and hit initialize button. You have to wait until the initialization is complete for 10 steps.

    Time to solve;

    Now double click on Run calculation and give the number of iteration to be done. As concerned with 2D more iteration value can be given. It is recommended to give value more than 50 for steady state solution. I give 150. click on calculate.



    After solving a graph is plotted. End of solving but sometimes the solution may be converged as earlier before completing given iterations. Beauty of 2D models is that it reduces time.



    On ansys workbench you can able to see two check marks one after other.










  5. Step 5: Post Processing

    After solving close the window of Fluent and double click on results. This open up page.



    Appearance may vary and can be changed according to wish.


    Now time to view the result. For that click on contour and name it.



    When apply is hit you can see the contours of pressure.


    Even the contour can be smoothened by increasing the # of contour.


    Now the result looks like, after hitting apply:




    Now select various parameters like velocity, temperature etc., Even streamlined flow can be viewed like selecting icon next to contour select button and name it.



    Hit apply.









  6. Step 6: Conclusion

    This concludes the final view of 2D analysis in CFD. Hope you guys enjoys this.

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