Hiroshi Takeuchi asked 1 week ago
I’m facing a curious result using T6 with VPW analysis about Cdi numbers. In case of comparing the result with T2 analysis, the CD numbers in polar curves are similar however spanwise curves of induced drag coefficiency (Cdi) are very different. I checked both spanwise curves with exported file and confirmed that there is no large difference between T2 and T6 analysis regarding F.y number. What was caused this difference?
Type 2 (Fixed lift)
Triangles – Uniform doublet density
Mass = 100.000 kg
CoG_x = 0.011 m
CoG_z = 0.068 m
V∞ = 7.949 m/s
α = 3.500°
CP = (0.0533; -2.81e-11; 0.39) m
CL = 0.9449933
CD = 0.0167025
Type 6 (Control analysis)
Triangles – Uniform doublet density
Mass = 100.000 kg
CoG_x = 0.011 m
CoG_z = 0.068 m
V∞ = 7.919 m/s
α = 3.500°
CP = (0.0743; -2.41e-11; 0.385) m
CL = 0.9523579
CD = 0.0158894
T2 Spanwise
y(m) Re Ai Cd_i Cd_v
0.0625 546674 -0.63098 0.0119395 0.0080198
T6 VPW Spanwise
y(m) Re Ai Cd_i Cd_v
0.0625 544566 -0.536308 0.0692294 0.00802797
techwinder Staff answered 6 days ago
It’s a bug.
In the latest versions flow5 stores and displays in the 3d operating point views the local induced drag calculated from the pressure forces instead of the induced drag calculated in the far-field plane.
Importantly, the plane’s induced drag displayed in the polar views is unchanged and is the one calculated in the far-field plane.
This display bug will be corrected in the next release. Thanks for reporting it.
André
It’s difficult to say without knowing the plane and wing configuration. Differences are expected to occur between T2 and T6 at angle of attacks such that the upstream wake panels are in the same horizontal plane as the downstream wings. The VPW is intended to help solve this problem, however the solution can show large variatons around this critical aoa.
I’ll send you a personal message if you want to share the project file so that I can have a look.
André
Thank you for your quick response. I’ve just sent the project file to you.