Turbulent channel flow concentration profile and wall deposition of a large Schmidt number passive scalar

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Elsevier France-editions Scientifiques Medicales Elsevier
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The transport of a passive scalar within a turbulent plane channel flow has been theoretically analyzed by assuming that the Schmidt number Sc, associated to the molecular diffusivity of the passive scalar, is a large parameter. Throughout most of the channel cross-section the mean passive scalar density is constant, but adjacent to the walls a thin boundary layer develops embedded in the viscous sublayer, with a relative thickness of order Sc(-1/3). In this narrow region a passive scalar profile arises due to the non-vanishing flux normal to the wall. This profile is parameter independent (universal) and leads to a constant flux of passive scalar that results from the addition of both the molecular diffusion flux and the turbulent transport one. The Sc-asymptotic matching of this profile with the constant core value provides an analytical expression for the wall-normal flux that depends on the fluid dynamics of the carrier flow. By using a DNS code to solve the external turbulent flow, the analytical expression has been quantified and compared with empifical expressions based on experimental data, showing excellent agreement.
Conference on Observation, Analysis and Modelling in Complex Fluid Media held in honor of Roland Borghia, Marseille, FRANCE, JAN 31-FEB 01, 2005
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