Laser Doppler measurement of turbulence parameters in a two-dimensional plane wall jet

Abstract

A computer-controlled data acquisition system has been designed and constructed to automate measurement of turbulent velocity correlations in a two-dimensional turbulent wall jet. Measurements are made with a single component laser Doppler velocimeter system in a flow of air on a flat plate with stagnant surroundings. Measurements of a number of turbulence parameters have been completed and compared with existing hot-wire data. The measurements are made at two downstream locations at a Reynolds number, based on slot width, of 14 000. Earlier hot-wire data for a two-dimensional turbulent wall jet in stagnant surroundings show much scatter in the outer region where local turbulence intensities range from 40% to 70%. The laser Doppler velocimeter gives repeatable values and eliminates the bias in hot-wire measurements due to reversing flow and errors in corrections for high turbulence effects. The measured turbulent normal stresses are somewhat higher than those previously reported throughout the flow field. The turbulent shear stress is in good agreement with previous hot-wire results near the wall. Hot wires are shown to indicate low values of the Reynolds stress in the turbulent outer regions where they are affected by strong flow reversals. The new measurements agree well with predictions based on momentum integral methods.