PMARC-12 Neumann Patches

R. Harris

Hello;

I have some PMARC-12 questions that I was hoping somebody could help me with.

1) My first problem is with using Neumann patches as lifting surfaces. As a test case I performed a run with a single rectangular planform lifting surface with an aspect ratio of 6 and an angle of attack of 10 degrees. Several things seem wrong with my results. First, the wake doublets all have zero strength. I ran the code in the debugger and it appears that the wake doublet strength is calculated in subroutine WAKDUB by subtracting the "upper" and "lower" trailing edge body doublet strengths as described in the users guide and elsewhere. The problem is that subroutine WAKINIT seems to assign the same panel index for both the upper and lower body panels along the wake separation line for Neumann patches. The result is that the doublet strengths cancel. Is this a known problem with the code or am I using it improperly? I can provide my input files if that helps. The other problem is that the lift coefficient seems to be a strong function of the direction which the surface normal is pointed. Any thoughts on these two points would be greatly appreciated.

2) I've been running some "thick" NACA 4 digit series symmetric airfoil sections with the same planform and angle of attack. The lift coefficient seems to be a much stronger function of foil thickness than I would expect from looking at, say, 2-D section coefficient data from Abbot and Von-Doenhoff. Why is this?

Thanks.

Rick Harris