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 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 ow 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-crossow 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 arti 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.
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