Spatially correlated temperature fluctuations in turbulent convection

By measuring the degree of spatial correlation in temperature fluctuations at two points separated by a distance perpendicular to the mean flow, we are able to determine the viscous boundary layer thickness in turbulent convection. We demonstrate this method using water as the working fluid and find excellent agreement with directly measured results. Furthermore, from the most probable delay time for a thermal disturbance to successively pass the two temperature probes, we deduce the width of the mixing zone and again find very good agreement between the value obtained and that predicted by theory.