Simultaneous measurements of temperature and velocity fluctuations in a slightly heated jet combining a cold wire and Laser Doppler Anemometry

Simultaneous measurements of two velocity components and temperature are pe rformed combining Laser Doppler Anemometry (LDA) and cold wire thermometry. LDA is a common technique suitable for velocity measurements in turbulent jets where strong turbulence intensities and reverse flows may exist, but t emperature measurements in association with LDA are difficult because the f ine wire response is altered by the seeding deposit, so that the wire must be regularly cleaned. Results reported herein concern velocity-temperature correlations, as well as velocity and temperature marginal probability dens ity functions and temperature (or velocity) probability density functions c onditioned by the sign of the velocity (or temperature) fluctuation. The ev olution of these various quantities is analysed in order to better understa nd the mixing properties in the near-field of a turbulent jet where the ini tial conditions still have a strong influence. It is shown that, while the velocity field tends to relax rather quickly (within a few nozzle diameters from the exit) to almost gaussian statistics, the temperature properties a re still significantly skewed towards the hot jet exit temperature until x/ D-j about 7-8. On the contrary, the signature of the cold ambient temperatu re vanishes rather quickly. (C) 2000 Elsevier Science Inc. All rights reser ved.