suction simulation on an airfoil using fluent

For my final year project, I am implementing suction on the NACA 23012 airfoil to improve aerodynamic performance, however, after specifying a suction inlet as a velocity BC and inputting the necessary data, my lift values are too high and oscillating. (for 0 AoA, Cl=4)

The velocity at the suction slot is half that of the velocity at the inlet of the flow domain. the turbulent intensity is 0.01%

the Reynolds number is 6,000,000 and the flow is subsonic incompressible.

How best do I implement suction in the simulation and specify it's corresponding boundary conditions?

Is the suction a pressure inlet or outlet?

Also, since the pressure at the suction slot is less than the atmospheric pressure, do I put a negative sign when inputting the gauge pressure?

Thanks.

Comments

  • RobRob UKForum Coordinator
    edited June 2019

    What you've set sounds sensible. How do the mesh and flow field look? Post images into the message as staff are not allowed to open attachments. 

  • akin3rdakin3rd Member
    edited June 2019

    here is the mesh

     

    the close-up view of the mesh;

    the pressure field about the airfoil

    the velocity field:

    and the lift coefficient at 0 AoA:

    to keep things in perspective, the lift coefficient value for the same airfoil without suction is about 0.12.

    The boundary condition that is best to simulate suction is what I am after. is it a pressure outlet or inlet? or a velocity inlet or mass flow rate inlet? 

    Thanks 

  • RobRob UKForum Coordinator
    edited June 2019

    Assuming it's incompressible flow a velocity boundary is fine. Otherwise you need to decide whether it's a fixed pressure or massflow system.  

    I'd also review the mesh: from the look of it you've over refined some regions and not been overly careful with the jump in cell size. Have a look for the Youtube air/aero foil videos. Also remember you need to mesh for the airfoil shape AND suction port. 

  • akin3rdakin3rd Member
    edited June 2019

    by meshing for the suction port, do you mean I cant just take a bit out of the airfoil wall (which is what i did) and create a new boundary condition?

    closely looking at the pictures of the mesh and the flow domain I attached as requested, there is no suction cavity present. Just a part of the upper surface of the airfoil that has been set as a suction BC. Basically, the flow is being sucked into nothing as what I am after is the effect of suction on the airflow around the airfoil and subsequently aerodynamic performance.

    could you please provide a pictorial representation of what you mean ( if you have any).

    With regards to the mesh, is the jump in cell size around the airfoil wall or after the trailing edge?

    Thanks 

     

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