Note on the suppression of transient shear-flow instability by a spanwise magnetic field

Shear flow is prone to transient instability in which perturbations having little or no variation in the streamwise direction can grow linearly for a long time if the Reynolds number is large. This behaviour is known to provide a trigger for the development of secondary instabilities and transition to turbulence. It is shown by a simple analysis of Kelvin modes that a spanwise magnetic field is efficient in suppressing this transient instability and therefore in inhibiting the transition to turbulence.