ORIGINAL: zhuxiyu
Thank you guys for all of this great information. Does the lift and drag coefficient in air vary much with the size of the foil? What I am trying to do is to do the CFD model, but I am not sure if my lift and drag results will be correct. That is why i want to compare my results to a relatively standard value. Thank you again.
CFD = Computational Flow Dynamics? Or is this something else?
As noted by the others already airfoil performance varies greatly as the Reynolds number falls. More importantly at the very slow or very small region is that the flow dynamics tends to collapse at the extreme low Re's. Xfoil, being designed and written to closely model the flow behaviour noted by Eppler and Selig, does a fairly decent job of indicating the range of size and speed where the flow becomes unpredictable. If you run Xfoil and lay in numbers in the 10K to 100K range you'll see that the lower ones all look like jagged broken glass. Then at some point there'll be one curve that looks semi normal and for numbers higher than that they smoothen out and look like siblings just like you'd expect to see from higher numbers. The jagged results of the lower Re's are indicative of the unstable back and forth separation bubble behaviour that can occur at the very low reynolds numbers such as found on smaller and slower models.