A Diffuser containing a fan inside analysis

It is a diffuser in it there is a fan

Simulation in ansys  fluent

Fan speed = 4000 rpm

Quantities to determine :-

  1. Pressure variation
  2. Velocity variation
  3. Flow animation
  4. Flow rate generated due to the fan rotation

I am new to the ansys software so I am not much acquainted to it. I have done this simulation in ansys fluent taking the inlet of the diffuser as a velocity inlet and outlet as a pressure outlet.The problem in this is that I am not able to see the result even if all the calculations are completed successfully. I tried to show and  contour and streamline but it does not show anything.  

I am attaching the iges file of the design.

Please help me!!


  • KremellaKremella Forum Coordinator
    edited July 20


    As Ansys employees, we are not able to download attachments from these posts. Could you please post the images directly here and we should be able to help?

    Are you doing your post processing in CFD post? Or are you using Ansys Fluent for this?


  • edited July 20
    I have tried in both but it is not showing anything..
  • RobRob UKForum Coordinator
    edited July 20

    Please post screen shots of what you're trying to plot & the results. 

  • edited July 21

    The design is open in design modeller. As you can see it has 2 bodies a diffuser and inside it there is a fan.

    Above I have given all the step by step procedure which I have followed for doing analysis. I am not able to find any of the quantities which I have told earlier in my first post. I am also getting an error named that velocity is not a variable. Please help me!

  • KremellaKremella Forum Coordinator
    edited July 21

    Do you have a converged solution? Can you show the residual plot (along with any monitors you might have created) in Fluent? Also, are you able to plot the velocity contour in Fluent?


  • edited July 21

    This above shows the method I used.

    This type of floating point error occured, than I pressed OK and I got this :-

    This are the above residual plot. I don't know whether my solution converged or not . 

    It shows whole black color. I am not getting what it shows?

    This above is the velocity contour, it shows whole blue but in reality it should vary as this is a diffuser. It should be highest in input and lowest in the output and the pressure should be the lowest in input and highest in output.

    This is the X-Y plot about plane 5 , it shows nothing..

    Please help! I am working on this project and I am in urgent need to do the simulation. 

  • edited July 21

    I am also giving some insights on my mesh quality :-

    I have used for the diffuser and fan hex dominant method for meshing.


  • KremellaKremella Forum Coordinator
    edited July 22


    Your solution did not converge. You got a floating-point exception error. This is the reason why you are not seeing the results.

    What is your mesh quality?

    Are you running MRF or sliding mesh analysis? Also, What are your boundary conditions?



  • edited July 24
    In the above post I have showed the pic of the mesh details. It also contains the mesh quality properties ,please reveiw it. I am new to ansys so I am not aware about the MRF or sliding mesh analysis.
    Boundary conditions :-
    1) I have defined the surface of the diffuser from which the air will enter as input.
    2) The surface of the diffuser from which the air will come out as output.
    3) The fan is defined as fan
    4) The outer perifery of the diffuser other than the input and output surface as wall.
    5) I have taken the input as velocity inlet and output as pressure outlet.

    I hope that these are the things that you asked for..thank you for helping me..
  • KremellaKremella Forum Coordinator
    edited July 24

    Please search for the axial fan tutorial on YouTube. You will find examples very similar to what you are trying to attempt. This should help you get to the right model set-up. 

    Could you please follow one of these examples and see if you can verify your model set-up? Please note that these are old videos and you might have some convergence issues with these settings. But, this set-up should provide you a good learning experience. 

    Also, please verify that the min orthogonal quality of your mesh is greater than 0.1 and max skewness is less than 0.9.

    Thank you.


  • edited July 27
    Thank you for helping.
  • KremellaKremella Forum Coordinator
    edited July 27

    You're welcome!

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