ESTIMATION OF VELOCITY SPECTRA IN VARIABLE-DENSITY JETS USING LASER-DOPPLER ANEMOMETRY

The present paper is concerned with turbulent jet flows in which the d ensity varies due to exchanges of mass. Such flows have gained some at tention over the last few years but, to our knowledge, this is the fir st time results are reported for the influence of density variations o n velocity spectra. Our measurements are obtained by laser-Doppler ane mometry and part of the paper is also devoted to testing several proce dures for estimating spectral densities from the randomly sampled data . Comparisons between turbulent helium and air jets confirm that the l ighter gas jet develops at stations nearer from the exit nozzle and th at the turbulent Reynolds number R-lambda remains the essential parame ter to describe the distribution of turbulent scales in strong variabl e density jets. (C) 1998 Elsevier Science Inc. All rights reserved.