Non-dimensionalization Cl and Cd from CFD results
 

Dear All,

First of all, I am so sorry if my post is out of topic. I would like to ask a question, which I also posted in the Researchgate:
https://www.researchgate.net/post/No...ating_airfoils [accessed Feb 28, 2016].

So basically I am doing CFD simulation of a rotating airfoil (VAWT), and the standard output of aerodynamic coefficients from the code is based on the inflow velocity. Here is my question:

I am calculating lift (Cl) and drag coefficients (Cd) for a rotating airfoil. Let's say the tip speed ratio (TSR) is equal to 2 and the wind speed is 8m/s. I noticed that due to rotational motion, the airfoil will see an additional velocity tangential to the airfoil body, therefore Cl and Cd should be calculated based on the relative velocity (Vr).

However, when I did this, Cl and Cd were not comparable with the aerodynamic polar in static conditions. Since the dynamic stall (DS) should occur, the lift is expected to increase, and this was not observed when I used (Vr) as reference. Cl was significantly reduced compared to the static polar. Nevertheless, this was not the case when the wind speed was used as the reference. Cl was increased and behaved as usual DS characteristics. Please see the attached picture.
As a note, DS characteristics such as the leading edge vortex creation and convection were clearly observed. So, I am sure that DS is occurring.

Can somebody suggest me an idea? Thanks in advance for your response!

Galih

I found the answer already, cheers...
Galih