Absolute inviscid instability of a ring jet with back-flow and swirl

The absolute instability of a ring jet with back-flow and swirl has been in vestigated on the basis of the inviscid linearized theory for incompressibl e flow. An axisymmetric disturbance mode is found to be only convectively u nstable. The first azimuthal mode can become absolutely unstable, if the ri ng jet has a back-flow on the jet axis, and an additional swirl can increas e the instability. However, for large swirl the absolute instability is sup pressed. A ring jet without back-flow becomes absolutely unstable only in t he presence of swirl. (C) Elsevier, Paris.