Temperature dissipation in a turbulent round jet

Abstract

Parallel cold wires were used to measure the temperature derivative, in each of the three spatial directions, in the self-preserving region of a turbulent round jet. The temperature derivative variances were inferred from the correlation method and from the temperature derivative spectra after correcting these for the effect of wire separation. Both methods yielded fully consistent results for the components of the average temperature dissipation: the radial and azimuthal values are nearly equal and only slightly larger than the axial component. The resulting departure from isotropy of the temperature dissipation is small, especially when compared with results in other free shear flows. The high-wavenumber behaviour of the corrected temperature derivative spectra conforms closely with isotropy on the jet axis but small departures occur away from the axis. Conditional averages, based on spatially coherent temperature jumps, indicate that, while the organized motion makes a significant contribution to the temperature variance, its contribution to the temperature-derivative variances is small.