(325d) Flow Structure Effects on Turbulent Transport for Channel and Plane Couette Flow

Turbulent flow and passive heat transfer in plane Poiseuille and plane Couette flows at low Reynolds number have been studied using direct numerical simulation (DNS) in conjunction with the Lagrangian scalar tracking (LST) method [1,2]. Results from DNS/LST have shown agreement with experimental data. Using this method allows further studies that are difficult to conduct with experiments, such as the investigation of how the structure of the turbulent flow affects heat transfer. There is some speculation about the correlation between the velocity structure and the temperature field. Velocity and temperature streaks have been reported for low Prandtl number, Pr, fluids in turbulent channel flow using DNS [3, 4]. These prior investigations have found that the velocity and the temperature streaks show a strong resemblance to each other. In the present work, two types of velocity profiles are studied: one is plane Couette flow and the other is Poiseuille channel flow, and the Pr ranges from 0.1 to 50,000. The instantaneous velocity field and the thermal fields are visualized in a plane normal to the direction of the flow to investigate the connection between the turbulent structure and the mechanism of turbulent heat transport. Length scales are calculated for the available range of Prandtl numbers at different locations across the channel. It appears that larger scales are contributing to the transport of heat as the distance from the wall increases, as is the case for momentum transfer. Turbulent Prandtl numbers can then be predicted by finding the ratio of the turbulent length scales for flow divided by the turbulent transport length scales, and compared to available models for the turbulent Prandtl number.

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