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Measurement of turbulent dispersion behind a fine cylindrical heat source in a weakly sheared flow

Published online by Cambridge University Press:  26 April 2006

Myung Kyoon Chung
Affiliation:
Korea Advanced Institute of Science and Technology, Seoul, Korea
Nam Ho Kyong
Affiliation:
Korea Institute of Energy and Resources, Daeduck, Korea

Abstract

Turbulent structure in a turbulent scalar dispersion field behind a fine cylindrical heat source in a weakly sheared flow is experimentally investigated and previous computational turbulence models for third-order scalar transport terms in the second-order turbulence equations are assessed with the present data.

The mean temperature and r.m.s. temperature profiles are found to be almost Gaussian even in the uniform shear layer. Decay of the peak temperature, mean dispersion and half-widths of the mean temperature and the r.m.s. temperatures are well correlated with corresponding data on the scalar dispersion behind an elevated line heat source in the turbulent boundary layer.

Normalized streamwise heat flux $\overline{u\theta}$ changes appreciably with the downstream distance owing to the influence of the uniform mean shear, whereas normalized vertical heat flux $\overline{v\theta}$ remains the same with the downstream distance. The timescale ratio R between temperature and velocity fluctuations varies from 0.3 to 1.3 across the stream and it asymptotes to a value 0.5 at far downstream.

Assessment of previous models for third-order moments with the present data reveals that application of a composite timescale between the dynamic timescale and the thermal timescale to the simplest gradient transport model yields a better overall prediction performance than any existing models, including Lumley's algebraic model equations for the moments. It was found that the timescale for the streamwise transports of $\overline{u\theta}$ and $\overline{\theta^2}$ is larger than that of lateral transports of $\overline{v\theta}$ and $\overline{\theta^2}$.

In addition, since the experiment isolates 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.

Type
Research Article
Copyright
© 1989 Cambridge University Press

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