Azimuthal instability in an impinging jet: adiabatic wall temperature distribution

The present work has been aimed at gaining some new insights into instability phenomena arising when an air jet impinges on a flat plate under certain conditions. At a critical Mach number, depending on the impingement distance, the jet loses its circumferential appearance with the formation of evenly equidistant azimuthal structures, whose number and location depend on the nozzle geometry and on the flow conditions. The instability is investigated in terms of pressure and adiabatic wall temperature; the latter is measured by means of an infrared scanning radiometer. Entrainment effects are found to play a key role in the priming and evolution of the instability.