LASER-DOPPLER ANEMOMETRY MEASUREMENTS IN AN AXISYMMETRICAL TURBULENT JET

The present study was performed to investigate experimentally some asp ects related to the characteristics of turbulent jet flow using laser Doppler anemometry (LDA) as a measuring technique. It includes the fol lowing: (1) investigation of the effect of the velocity bias on the ex perimental results of the mean and fluctuating velocities, (2) study o f the effect of upstream conditions on the mean and turbulent velocity profiles at the jet exit plane, (3) measurement of the decay rate of the center line longitudinal mean velocity and compared results with e mpirical correlations, (4) examination of the achievement of self-pres ervation of the jet flow, (5) investigation of whether the flow is app roaching isotropy, (6) measurement and documentation of the distributi on of the radial mean as well as turbulent velocity profiles. The axia l and radial velocity components were measured simultaneously at the s ame location of the flow using a 5 W argon-ion laser Doppler anemometr y. The LDA operated in the fringe Pattern mode, in two-component color s, and in the backscattering detection mode. The present study was car ried out for the Reynolds number Re-e=10(4) (based on the nozzle exit diameter D and the center line longitudinal mean velocity at the nozzl e exit diameter U-e) up to an axial distance of 45D. In addition, seve n cases of initial upstream conditions were investigated. The obtained results revealed that no correction for the velocity bias is needed w hen the turbulence intensity is low (below 15%). Further, the mean vel ocity profiles cannot uniquely identify the state of a jet flow. In ad dition, the effect of the upstream conditions is pronounced mainly in the near field region. Meanwhile the jet flow approaches a certain deg ree of isotropy in the far field. (C) 1996 American Institute of Physi cs.