Difference between Cd_i and Cd_v

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Hiroshi Takeuchi asked 10 months ago

Does anyone explain to me the difference betwen Cd_i and Cd_v with detail ? I believe Cd_i ‘s ‘i’ is inviscid and Cd_v ‘s ‘v’ is viscous. In case of using ‘ from Cl – xflr5 method’ option within the analysis definition, Cd_v is based on the polar data of airfoil, I guess. Is Cd_v is the viscous part of Cd number or the total ( inviscid plus viscous ) Cd number ? I’d like to confirm that if I should use Cd_v number only in case of calculate the local drag force on main wing or not.
Regards,
Hiroshi

Main Wing
y(m) Re Ai Cd_i Cd_v Cl CP.x(%) Trans.top Trans.bot Cm_i Cm_v Bending.mom Vd.x Vd.y Vd.z F.x F.y F.z 
-16.950000 133257.777027 -1.559368 0.009003 0.015059 0.330708 0.392781 0.814491 0.990264 -0.044319 0.143337 0.000000 0.000000 -0.074104 -0.191920 -0.017404 0.112491 0.284553

techwinder Staff replied 10 months ago

Hello,
Yes, CD_i is the inviscid part of the drag and CD_v is the viscous part.
Cd = Cd_i + Cd_v
I tried to explain things in the “Theoretical background” presentations which you will find linked on the xflr5 web page.
Hope this answers the question.
André

Hiroshi Takeuchi replied 10 months ago

Thank you for your quick response. I understand the definition of Cd_i and Cd_v and will refer the presentation later.

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