Three-Dimensional Vortex Interactions.

Abstract : Three-dimensional vortex interactions were investigated in jets with slanted, indeterminate origin exit nozzles, and in mixing layers behind a splitter plate with a swept trailing edge. Flow visualization images were quantitatively processed to characterize complex three dimensional vortex interactions in non axisymmetric jets. Phase conditioned pulsed laser sheet illumination was used to obtain a series of sectional images while rotating the asymmetric nozzle. The sectional images were recombined into an unwrapped representation of the developing vortex systems in the shear layer. Partial pairing of sections of adjacent vortex systems was shown to be responsible for asymmetric shear layer growth. Flow visualization in the flow behind the swept trailing edge showed that two families of instability waves can develop with different orientations with respect to the trailing edge angle. Excitation was shown to enhance waves with orientation parallel to the trailing edge or perpendicular to the mean flow direction, depending on excitation frequency. Streamwise wavelengths of the two wave families were related by their angular separation. Keywords: Fluid mechanics; Shear layers; Jet flows; Passive control; Active control; Image processing; Control of turbulence; Asymmetric nozzles; Slanted nozzles; Indeterminate origin nozzles; Pulsed laser flow visualization; Mixing layers; Instability waves.