On absolute instability of free jets

We analyze the nature of instability (absolute or convective) of a jet velocity profile obtained in preceding experimental studies. It is surprisingly found that local instability of the velocity profile near the orifice is absolute. Physical mechanism of absolute instability is revealed. Hence, absolute instability of a jet does not require counterflow, as was considered before. However, the instability observed in experiments is convective due to rapid spreading of the jet downstream from the orifice and the change of instability nature from absolute to convective. Possible methods of the prolongation of local absolute instability and its applications are discussed.