WIND User's Guide - Keyword Reference, ROLL

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ROLL - Specify roll about one of the coordinate axes

ROLL {X | Y | Z} rat x1 x2

The roll keyword allows the user to specify roll about one of the coordinate axes.

rat Rotation rate in radians per second
x1, x2 Coordinates of the center of rotation. The coordinates specified by x1 and x2 depend on the rotation axis, as shown in the following table:

Rotation axis x1 x2
X y z
Y z x
Z x y

Note that in this mode, the calculation is done in inertial space, and the grid is assumed to roll through inertial space at the specified rate. The grid velocity imparts the rotating component. Thus, in order to show the velocity relative to the rotating axes, the roll component of velocity must be subtracted (via the CFPOST post-processing package or another mechanism).

Note also that, unfortunately, unless ROLL is used in a true time-accurate mode which moves the grid each time step (not currently available), as well as giving it velocity, the ROLL capability neglects the rotational potential energy, and so is not correct for high rotation rates.

With this keyword, the velocity vector must be aligned with the coordinate axis. (To get an angle of attack, rotate the grid in GMAN.)

See Also: ROTATE