Turbulent scalar transport behind a line heat source in a uniform shear flow

Abstract

Turbulent dispersion from a line heat source in nearly homogeneous shear flow is investigated and computational turbulence models of the third order scalar transport terms in the Reynolds shear stress equation and the kinematic heat flux equation are developed. For this study, a special wind tunnel has been designed and manufactured which produces a turbulent uniform shear filed. A combination of X-type hot wire for the measurement of velocity fluctuations and a cold wire of $0.6 ㎛$ for the measurement of temperature fluctuations has been devised to simultaneously obtain the cross correlations between the velocity and temperature fluctuations at various orders. The experiments have been performed at two different heating rates. Scaling the data by local characteristic scales enables us to represent the data in a consistent way which is almost independent of the heating rates and the lateral transpart of $\overline{u\theta}$ and \overline{\theta^2}$ is larger than that of lateral transport of $\overline{V\theta}$ and $\overline{\theta^2}$,. Previous models for 3rd order moments have been assessed with the experimental data and it was found that application of a composite timescale between the dynamic timescale and the thermal timescale for the third order moments to the simples gradient transport model yields best overall prediction performance over any existing models including Lumley``s algebraic model equations for the moments. In addition, since the experiment has isolated the effect of uniform mean shear on the turbulent scalar transport, experimental data accumulated by the present study will be useful for further development of more refined second order turbulence models for non-isothermal turbulent flows.