Laser Doppler anemometry measurements in an axisymmetric turbulent jet

Abstract

The present study was performed to investigate experimentally some aspects related to the characteristics of turbulent jet flow using laser Doppler anemometry (LDA) as a measuring technique. It includes the following: (1) investigation of the effect of the velocity bias on the experimental results of the mean and fluctuating velocities, (2) study of 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 empirical correlations, (4) examination of the achievement of self-preservation of the jet flow, (5) investigation of whether the flow is approaching isotropy, (6) measurement and documentation of the distribution of the radial mean as well as turbulent velocity profiles. The axial and radial velocity components were measured simultaneously at the same location of the flow using a 5 W argon-ion laser Doppler anemometry. The LDA operated in the fringe Pattern mode, in two-component colors, and in the backscattering detection mode. The present study was carried out for the Reynolds number Ree=104 (based on the nozzle exit diameter D and the center line longitudinal mean velocity at the nozzle exit diameter Ue) up to an axial distance of 45D. In addition, seven cases of initial upstream conditions were investigated. The obtained results revealed that no correction for the velocity bias is needed when the turbulence intensity is low (below 15%). Further, the mean velocity profiles cannot uniquely identify the state of a jet flow. In addition, the effect of the upstream conditions is pronounced mainly in the near field region. Meanwhile the jet flow approaches a certain degree of isotropy in the far field.