Travelling disturbances in rotating-disk flow

The stability curves for traveling disturbances in rotating-disk flow are computed using the sixth-order system of incompressible linear stability equations. The neutral curve has two minima for disturbances with positive frequencies as found earlier by Malik (1986) for stationary disturbances. The upper branch minimum occurs at omega = -2.9, R = 283.6 while the lower branch minimum occurs at omega = 7.9, R = 64.46, where R is Reynolds number. There exists a critical angle of approximately -35.34 deg below which all the waves are linearly damped.