Evolution and Control of Transverse Jet Instabilities

This experimental study focuses on the quantification of nearfield shear layer instabilities associated with a round gaseous jet injected normally into crossflow. The control of these instabilities via acoustical jet forcing has been the subject of prior and ongoing studies by our group(M'Closkey, R. T., King, J. M., Cortelezzi, L., and Karagozian, A. R., JFM), Vol. 452, pp. 325--335, 2002 for a number of specific jet, crossflow, and excitation conditions. In the present study, in the absence of acoustical forcing, preferred mode instabilities associated with jet shear layer vortices are observed and quantified for a wide range of jet and crossflow conditions. Evidence of the merging of these vortical structures further downstream, along the upper edge of the transverse jet, is also quantified. These transverse jet instabilities and associated merger processes are similar in nature to those for the free jet, yet are stronger in magnitude and are associated with systematically higher characteristic jet Strouhal numbers. The instabilities are further observed to be influenced by the injection wall boundary layer. The benefits of subharmonic transverse jet forcing in terms of optimized jet penetration and spread are explored.