# Derivative of lift with respect to angle of attack

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 April 5, 2016, 15:42 Derivative of lift with respect to angle of attack #1 New Member   Ryan Barrett Join Date: May 2015 Posts: 15 Rep Power: 9 I have been trying to use the adjoint method to get the lift derivative with respect to angle of attack for a 2D airfoil. I have been trying to use the ROTATION design variable, but I am confused on the syntax. I have been using Code: `DEFINITION_DV = (6, 1.0 | airfoil | x_Axis, y_Axis, z_Axis, x_Turn, y_Turn, z_Turn )` But I am confused on what to put for x_Axis, x_Turn, etc. For a 2D airfoil if you wanted to find the derivative of the angle of attack would you turn the z axis a small amount like this?: Code: `DEFINITION_DV = (6, 1.0 | airfoil | 0, 0, 1, 0, 0, 1e-4)` Thanks! kmandar likes this.

May 24, 2016, 23:17
#2
Senior Member

Heather Kline
Join Date: Jun 2013
Posts: 309
Rep Power: 12
Quote:
 Originally Posted by Ry10 I have been trying to use the adjoint method to get the lift derivative with respect to angle of attack for a 2D airfoil. I have been trying to use the ROTATION design variable, but I am confused on the syntax. I have been using Code: `DEFINITION_DV = (6, 1.0 | airfoil | x_Axis, y_Axis, z_Axis, x_Turn, y_Turn, z_Turn )` But I am confused on what to put for x_Axis, x_Turn, etc. For a 2D airfoil if you wanted to find the derivative of the angle of attack would you turn the z axis a small amount like this?: Code: `DEFINITION_DV = (6, 1.0 | airfoil | 0, 0, 1, 0, 0, 1e-4)` Thanks!
Since the angle of attack is set at the freestream, you should look into whether the Sens_AoA output is appropriate to your purpose.

In terms of the rotation variable, I took a peak in the code and it looks like it takes the first three numbers as the origin of rotation, and the second set of three as the other end of the rotation axis. The value of the design variable is the angle, in degrees. In other words, you should specify (0,0,0, 0,0,1) to have a rotation axis pointing in the positive Z direction with a rotation center of (0,0,0).

The syntax for defining a rotation using an FFD box is also listed in the config_template file:

% - FFD_ROTATION ( FFD_BoxTag, x_Orig, y_Orig, z_Orig, x_End, y_End, z_End )

 Tags angle of attack, gradient, su2