Modelin Multi Element Airfoils

Yashwant Ganti

Hi, I need assistance in modeling a multi-element airfoil. It consists of a 25% T.E flap. The problem I am facing is that I am getting low Cl values for flap deflection of 30 deg. I am getting a value of 1.8 whereas the NACA23015, which is very similar to this airfoil shows 2.5 at the same deflection. I generated my mesh from the following tutorial: instruct1.cit.cornell.edu/courses/fluent/airfoil.

Even though, the tutorial is for a simple airfoil, I used a similar C type grid, with two cuts on the upper and lower surface at the end of the main element and meshed the gap between the main element and the flap using Quad elements and a Map scheme. This gave me a mesh in the form of the streamline pattern which would be expected in the gap. I have a doubt regarding the branch cut at the end of the flap, does it have to follow the flap surface and hence be inclined at the same angle to the horizontal as the flap or can it be horizontal as I have made it. I suspect the problem is with my grid generation and I am in a dilemma about using structured/unstructured grids as I have seen both being used in literature. I am new to grid generation and would greatly appreciate any help.

Also if i were to use a turbulence model, which would be the best. I used a k-epsilon model, with the default values, but when I looked at the y+ values, they were in the range of 300-500. But in the literature they say that y+ should be around 10-30. Please advise me on how to use the correct turbulence model for this kind of a problem.

Thanks, Yashwant.