Rationale behind frozen wake assumption

Dear Avi,

Although states associated with the dynamic wake are not included in a linearized model based on frozen wake, linearization with frozen wake is a better approximation of the linearization one would obtain with dynamic wake than one would obtain with equilibrium wake. As shown in the following forum topic: Gain Scheduling - #10 by Jason.Jonkman (particularly Ville’s post dated Nov 25, 2010), the sensitivity of power to pitch with equilibrium wake shows a similar trend to that of frozen wake, but (inaccurately) shows a loss of control authority—whereby the sensitivity is near zero—at rated conditions. As such, the use of frozen wake in the linearization process is recommended.

Linearization with frozen wake is now a standard feature of the linearization capability of FAST v8 with AeroDyn v15.

I hope that helps.

Best regards,