How bladed determines the gradient for dynamic stall calculations?
Bladed versions affected: all Bladed versions adopting two-point approximation method.
Date of last article update: 2 March 2023
Bladed determines the gradient based on the two distinct values obtained from the lift polar (to be precise normal force polar) provided by the users. One is at an angle of attack equals zero and the other one is at an angle where the normal force becomes zero. This is illustrated in figure below. A linear slope can then be determined. In case of semi-symmetric airfoil where the zero lift angle of attack is located at angle of attack equals zero, the gradient of the polar exactly at this location is used as the chosen value. From Bladed 4.13, a new method namely "linear fit gradient" approach was introduced and is more robust than the two-point approximation method, see Linear fit gradient method