Does Cl and Cd values of an airfoil change with steady and transient simulation?

Does Cl and Cd values of an airfoil change with steady and transient simulation?

 

Welcome to the forum.

What do you mean by "steady" and "transient"? How close to stall? Va or AoA transients? It all depends. Do we really want to get into the turbulent boundary layer issues?

 

Cl and Cd depend on both speed and angle of attack. You get curves like those below for a steady speed and steady angle of attack, meaning that when you change angle of attack, you wait for any transient phenomena to pass before you take a measurement.


I an article that explained why a rudder broke, I read that when you change angle of attack very quickly, as might happen to flow over underwater foils in a broach, then coefficient of lift may rise well above the steady state maximum. I have not yet found an open access scientific paper showing actual measurements, but these paywalled papers look promising, judging by their abstracts:

https://arc.aiaa.org/doi/abs/10.2514/3.45507

https://arc.aiaa.org/doi/abs/10.2514/3.45183?journalCode=ja

 

In "real world" testing, you often find a significant amount of hysteresis in those coefficients, depending on time rate of change, increasing or decreasing AoaA and so on. There is also a variation in sensivity between profiles and 3D conditions. So yes, you should find differences in decent simulations as well.