MANIPULATION OF A JET IN A CROSS-FLOW

The effect of forcing on the mixing and velocity field of a jet in a c ross flow is investigated for a jet-to-cross flow velocity ratio of R = 1.0 using reactive-Mie-scattering flow-visualization and two-color P article Image Velocimetry (PIV) techniques. Reactive-Mie-scattering im ages are used to assess the effect of forcing on molecular mixing, whe reas double-exposed two-color PIV images are employed to obtain instan taneous velocity and corresponding vorticity distributions. The jet em anates from a square conduit and is manipulated by four piezoelectric actuators - one mounted along each side of the jet conduit near the je t-exit plane. Time-and phase-averaged distributions of velocity and rm s velocity fluctuations in the x-y plane z = 0 are also obtained. A no vel approach is employed for processing jet and cross-flow fluids base d on the size of the seeding particle. The present results show that w hen 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 th e 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. Manipulatio n 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 enhancem ent. Unlike in streamwise forcing where the jet fluid remains mainly i n the central portion of the spanwise surface, spanwise forcing induce s strong spanwise jet undulations. (C) 1998 Elsevier Science Inc. All rights reserved.