Experimental observations of instability modes in a rectangular jet

The instability modes of a jet issuing from a rectangular nozzle of aspect ratio 4 have been studied experimentally at exit Mach numbers ranging from 0.03 to 1.5. Depending on the exit Mach number, several distinct characteristics are identified according to the arrangement of the flow structure with respect to the jet centerline. In the very low velocity range, U ≤ 20 m/s, a symmetric mode prevails. An antisymmetric mode dominates at all other Mach numbers, except in the range 0.6 ≤ M ≤ 0.85, where both symmetric and antisymmetric modes exist and there is a continuous switching between them