How to calculate the drag for a rotating wheel?

what the boundary conditions that is to be given while doing it in phoenics software?

You can start using the second law of Newton.

Need a clear definition of drag.

If the drag is defined by the shear stress only, you need to know what is the principle direction of the drag.

In Phoenics it is possible to get the value of velocity components which can be used to evaluate the shear stress at the wall.

The second question may depend on the frame of reference and the translation of the rotating wheel. Hope other will correct me if I am wrong

Thank you for your reply. Let me try in the mehtod that you said. This is related to my project work, Aerodynamics of Rotating Wheels, so im working on it. Can you give me a suggestion to do in Phoenics like in which turbulence models can I do that. I have got some papers related to this topic and in all they have take the k-epsilon turbulence model. Any suggestions..?

I have an experience on rotating disc. Does it similar? If so, the drag that you have briefly mentioned is normally called windage (let me know if I am wrong). You need to know the windage power in order to approximate how much energy required to rotate the disc at the precribed rotatinonal speed.

If you are considering the rotating disc system, k-e model with wall function formulation has been used at high rotatinonal speed. In some other rotating disc configurations, the turbulence model may requires modification for improving the main flow predictions. In this case, you may try other advanced turbulence models available in PHOENICS. Please let me know if you have manage to compute ones.