Learning Forum

[maxning]

I have a outer mold line model of a blended wing body UAV and are trying to find whether the aircraft is stable by seeing lift-induced-moment on the UAV's aerodynammic center. I tried using the quarter-chord method, but I am not sure it could work on a blended-wing body. Is there a way to use ANSYS Fluent to find the aerodynamic center of my UAV?

[mcoderon]

Hello,
depending on the profile of the wing and the flying speed the aerodynamic center could deviate from the quarter chord. This should give you an idea whether you have a situation close to the thin airfoil theory the quarter-chord position is based on.
You can find on textbooks generic formulae based on the first and second derivative(wrt the angle of attack) of the LE moment and the normal and tangential forces acting on the wing section that can be combined to find the 2 coordinates of the local aerodynamic center (on a plane). This means that you need to get the solution on multiple angles of attack to estimate the derivatives and then extend the analysis to a 3D case. Especially for complex models it is not just a 1 click solution.

[Farrukh Malik]

HI, couuld you kindly share this formula or a reference text in which it can be found. 

Secondly we can automate using parameter set to calculate cardinal forces at AOA how to compare calculated value of Cm to see where it doesnt change ? 

You help is highly appriciated. 

Regards.

[aitor.amatriain]

I would create a number of points along the chord, to then compute the pitching moment for different values of the angle of attack. The point where the moment does not vary is the aerodynamic center.