Manipulation of a jet in a cross flow

The effect of forcing on the mixing and velocity field of a jet in a cross flow is investigated for a jet-to-cross flow velocity ratio of R = 1.0 using reactive-Mie-scattering flow-visualization and two-color Particle Image Velocimetry (PIV) techniques. Reactive-Mie-scattering images are used to assess the effect of forcing on molecular mixing, whereas double-exposed two-color PIV images are employed to obtain instantaneous velocity and corresponding vorticity distributions. The jet emanates from a square conduit and is manipulated by four piezoelectric actuators - one mounted along each side of the jet conduit near the jet-exit plane. Time-and phase-averaged distributions of velocity and rms velocity fluctuations in the x-y plane z = 0 are also obtained. A novel approach is employed for processing jet and cross-flow fluids based on the size of the seeding particle. The present results show that when the jet is unforced, the "wake" of the jet contains a domain in which the magnitude of the velocity is very low compared to that of the cross-flow velocity, suggesting that the fluid within this domain is almost stagnant. When the jet is excited, the low-velocity domain in its wake is substantially reduced through vigorous mixing. Manipulation of the upstream and downstream segments of the jet sheer layer also leads to an increase in the jet penetration into the cross flow (up to 30% as compared to the unforced case) and substantial mixing enhancement. Unlike in streamwise forcing where the jet fluid remains mainly in the central portion of the spanwise surface, spanwise forcing induces strong spanwise jet undulations. (C) 1998 Elsevier Science Inc. All rights reserved.