Mixing enhancement via nozzle trailing edge modifications in a high speed rectangular jet

An aspect ratio 3 rectangular nozzle with design Mach number 2 was used to investigate the effects of trailing edge modifications on mixing enhancemen t and to explore the sources of streamwise vorticity at the fully expanded jet Mach numbers 1.75, 2.0, and 2.5. The trailing edge modifications are si mple cut-outs in the plane of the nozzle at the nozzle exit. The investigat ion of mixing and interaction between mixing layers and vortices was perfor med by the laser sheet illumination technique. Through surface flow visuali zations and wall pressure measurements, the investigation of the major sour ce of streamwise vorticity was carried out. In addition, the variation of t hrust generated by the nozzle with modified trailing edges was investigated . In the underexpanded flow condition, the major source of streamwise vorti city was determined to be the spanwise surface pressure gradient on the mod ification. Substantial mixing enhancement was achieved in this flow regime. On the other hand, in the overexpanded flow regime, the role of streamwise vortices in mixing and the source of streamwise vorticity were unclear, an d mixing enhancement was not substantial. No measurable thrust loss or gain was obtained for nozzles with trailing edge modifications, regardless of t he type of modification. (C) 1999 American Institute of Physics. [S1070-663 1(99)00509-7].