xiaoqing chen asked 3 months ago
Hello，I encountered a problem. When analyzing a simple shape using the T2 and T6 methods, there are differences in lift, drag, and lift-to-drag ratio, but they are all reasonable. However, the calculated Cpx values are significantly different,as the position of the wing is shown in the picture. Could you please help me check it out?
and the aerodynamic coefficients are 
xiaoqing chen answered 3 months ago
Hello,
A few preliminary comments about the mesh:
– The body’s mesh is not closed at the rear end; in the boundary element method used by flow5, all volumes must be closed otherwise the results are invalid.
– The panels of the front wing are not connected to the fuselage panels; this too is an invalid configuration in panel methods
– The fuselage’s mesh could be made coarser to speed up calculations; this should not affect the results in any significant way
The purpose of the T6 polars is precisely to improve the evaluation of the moments and pressure center.The main problem is the potential numerical interaction of wake panels with the body and wing panels. Wake panels can be displayed in the 3d view. In the present test case, they don’t seem to intersect which is good, but they are in contact which should be avoided if possible by modifying slightly the body geometry for instance.
Lastly when using T6 polars, the recommendation is to used a Vortex Particle Wake. The calculations are significantly longer, but the evaluations of moments and pressure center are much more reliable.
Hope this helps,
André