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-   -   Reason for Lift Coefficient Error (http://www.cfd-online.com/Forums/fluent/91550-reason-lift-coefficient-error.html)

jsuf August 15, 2011 05:12

Reason for Lift Coefficient Error
 
Hi everyone,

I've been running some simulations for an airfoil at various angles of attack (up to 6 degrees) with properties;

Re = 1000, laminar model, second order density based solver, free stream velocity = 1 (varied viscosity to obtain Re).

I'm getting lift and drag coefficient errors of order 5-10%, which for what I'm doing is ample. However, my drag coefficient is much more accurate than my lift. I'm curious as to what mechanisms would cause this, as I would expect drag to have a greater error (due to difficulties in resolving boundary layer).

Is there anything in particular in a mesh or Fluent setup which would affect lift in this way?

On a side note, I've also noticed that my 3D tests (allowing wing tip effects) are much more accurate than my 2D. I didn't expect this either. My 3D models are simple swept face versions of my 2D ones.

Thoughts?

Regards,
Josh


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