Measurements of turbulent velocity and temperature fluctuations in the wake of a sphere.

Abstract

Decay of mean, variance, and gradient variance of temperature and velocity were measured in the initially heated wake of a sphere in a water tunnel. Dissipation rates of turbulent kinetic energy by viscosity and of thermal variance by conduction within the wake were obtained by differentiation of the measured variance decay and also from direct measurement of the gradient variances. Both dissipation rates were found to decrease with stream wise distance x approximately as #~ 2-4 for up to 60 diam from the sphere. Small-scale temperature and velocity fluctuations were found to be approximately homogeneous for cross sections of the wake normal to the flow. No region of continuous turbulence was found in the sphere wake, even on the wake axis. A velocity spectrum measured on the wake axis normalized using the measured viscous dissipation rate was found to be in good agreement with spectra from other turbulent systems also normalized by Kolmogoroif scaling.