Laser Doppler Anemometry Study of a Turbulent Jet in Crossflow

Abstract

Introduction A JET in cross ow is an importantpracticalproblemencountered in turbine cooling, fuel injection, thrust vectoring (vertical/ short takeoff and landingaircraft),andmissile control.Experiments by Fric and Roshko1 and Kelso et al.2 show that there exists a complex vortical  ow in the near Ž eld. The main vortical structures include the horseshoe vortex, the counter-rotating bound vortex pair (CVP), the jet shear-layer vortices, and the upright wake vortices. The majority of experimentaldata existing in the literaturewere obtainedwith conventionalhot-wire anemometry,which is insensitive to  ow direction and can give large errors in regions of high turbulence. The present Note investigates the effect of velocity ratio on both mean  ow topology and skin friction for a round jet exhausting normal to a  at plate raised from the side wall of a wind tunnel. Two-component laser Doppler anemometry (LDA) was employed to measure mean velocity in threemutually perpendicularplanes of the  owŽ eld near the jet exit. The choice of test conditionshas been guided by a wish to supplement existing numerical and experimental studies, notably those of Yuan et al.3 and Kim et al.4; hence, a jet-to-crossow velocity ratio of 3.3was chosen.The lower velocity ratio of 1.3 was included in the study to show parametric effects for a turbulent incoming jet. Thanks to an artiŽ cially thickened turbulent boundary layer developingon the  at plate, skin friction could be determined from velocitymeasurements close to the wall on the planeof symmetry.Results to be presentedare based on a database,5 which includes distributionsof three components of mean velocity, vorticity, turbulent kinetic energy, and all Reynolds stresses.