ABSOLUTE INSTABILITY CONDITIONS FOR VARIABLE-DENSITY, SWIRLING JET FLOWS

Two different vortex sheet models are used to study the transition fro m absolute to convective instability in variable-density swirling jet flows. It is found that swirl enhances the tendency for absolute insta bility in a jet issuing into a non-swirling medium when the vortical c ore of the swirling how is small compared to the jet radius. When the size of the vortical core approximate the size of the let, the effect of swirl on promoting absolute instability is quite weak. The vend tow ard absolute instability is accentuated when the jet is heated relativ e to the ambient. If the how external to the jet also possesses swirl, the tendency tox ard absolute instability is increased when the jet s hear layer is centrifugally unstable according to Rayleigh's criterion (i.e., the circulation decreases with increasing radius) and is decre ased when the shear layer is centrifugally stable. (C) Elsevier, Paris .