Numerical Study of Coherent Structures of Turbulence with Large Wall-Normal Gradients in Thermophysical Properties
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Forced-convection heat transfer in a heated working fluid at a thermodynamic state near its pseudocritical point is poorly predicted by correlations calibrated with data at subcritical conditions. This is primarily due to the influence of large wall-normal thermophysical property gradients that develop in proximity of the pseudocritical point on the concentration of coherent turbulence structures near the wall. The physical mechanisms dominating this influence remain poorly understood. In the present study, direct numerical simulation is used to study the development of turbulence structures within a turbulent spot, which is a more controlled turbulence environment than a fully-turbulent boundary layer, with large wall-normal property gradients. It is found that during improved heat transfer, wall-normal density gradients accelerate the growth of the Kelvin-Helmholtz instability in the shear layer enveloping low-speed streaks through baroclinic vorticity generation. This causes hairpin vortices to form at a faster rate and to mutually interact more frequently.
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Copyright © 2015 the author(s). Theses may be used for non-commercial research, educational, or related academic purposes only. Such uses include personal study, research, scholarship, and teaching. Theses may only be shared by linking to Carleton University Institutional Repository and no part may be used without proper attribution to the author. No part may be used for commercial purposes directly or indirectly via a for-profit platform; no adaptation or derivative works are permitted without consent from the copyright owner.
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