Strategic Control of Transverse Jet Shear Layer Instabilities

摘要

This experimental study explores active control of the single gaseous jet in crossflow or transverse jet. Jet nozzlesnthat are flush aswell as elevated with respect to the injection wall are considered. These studies develop a strategy forncontrol based on separate experimental findings [Megerian, S.,Davitian, J.,Alves, L. S. de B., andKaragozian,A.R.,n“Transverse-Jet Shear-Layer Instabilities. Part 1. Experimental Studies,” Journal of Fluid Mechanics, Vol. 593,n2007, pp. 93–129], which indicate that the jet’s shear layer transitions to global instability when the jet-to-crossflownvelocity ratio R lies below a critical range. The R-dependent differences in the stability characteristics suggest thennecessity of a two-pronged approach to the controlled excitation of transverse jet penetration and spread, which isnexplored in this paper. For the transverse jets with relatively large R values, the jet shear layer exhibits convectiveninstability, hence even low-to-moderate-level sinusoidal forcing of the jet can control penetration and spread. For thencase where R is relatively low and the shear layer is globally unstable, the self-excited flow can be affected by strongnsinusoidal forcing at a frequency different fromthe dominantmode, but the effect on the jet’s actual penetration andnspread is not significant. For this regime, strong periodic jet forcing with a prescribed time scale that is related tonoptimal vortex ring generation is required to impact visible jet penetration and spread.