THE VISCOUS STABILITY ANALYSIS OF LONGS VORTEX

The viscous stability analysis of Long's vortex is performed. Some qua ntitative disagreements with the inviscid results of previous investig ators are reported. The truncation of the infinite radial domain into a small computational domain utilized in past investigations is found to be the source of these discrepancies. More important, for small flo w forces, a type-II Long's vortex is shown to be destabilized by pertu rbations having positive azimuthal wave number. Based on previous nume rical computations, it had been conjectured that these unstable eigenm odes may not exist. The stability characteristics of the unstable mode s are fully mapped and are presented in detail.