THE INFLUENCE OF TEMPERATURE ON THE MEASUREMENTS OF REYNOLDS STRESSESIN SHEAR FREE TURBULENCE NEAR A WALL

Temperature changes have a significant influence on the measurements o f Reynolds stresses in turbulent boundary layers. As compared to the s panwise velocity fluctuations the streamwise turbulence intensity is e specially sensitive to temperature deviations. Although this is a gene ral statement its importance is clearly elucidated in a shear-free tur bulence near a solid wall, since the mixing due to turbulence producti on is minimized in this flow. A consequence of temperature influence o n hot-wire measurements is that frictional heating from the wall has p roduced contradictory results in different experiments on shear-free t urbulence. In the current paper, measurements of streamwise and spanwi se turbulence intensities have been conducted at different wall temper atures, thereby simulating the contradictory results mentioned above. A simple model has been developed showing that the turbulence intensit ies are affected by both the rms. value of the temperature fluctuation s and the correlation between fluctuating temperature and velocity. Th ese correlations are measured and the developed model is used to expla in deviations in earlier measurements on sheer-free turbulence. Moreov er, the individual magnitudes of the two correlations in the temperatu re correction are estimated and their individual importance is discuss ed.