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arXiv · 1909.01652

Thermal transients in a U-Bend

Alex Skillen·Małgorzata J. Zimoń·Robert Sawko·Ryan Tunstall·Charles Moulinec·David R. Emerson
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Abstract

We study numerically the propagation of a hot thermal transient through a U-bend via an ensemble of wall-resolved large eddy simulations. Conjugate heat transfer between fluid and solid domains is accounted for. The flow is in a fully turbulent mixed convection regime, with a bulk Reynolds number of $10,000$, a Richardson number of $2.23$, and water as the working fluid (Prandtl number = $6$). These conditions lead to strong thermal stratification, with buoyancy-induced secondary flows, and the generation of a large and persistent recirculation region. The evolution of Dean vortices as the thermal transient passes is studied. It is found that baroclinic vorticity generation dominates over a large period of the transient, due to the thermal inertia of the wall. Gravitational buoyancy leads to a reversal of the counter-rotating vortex pair. The impact of this reversal on the swirl-switching and secondary-current losses is assessed. It is found that low frequency modes are suppressed in the reversed-vortex state.

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Alex Skillen, Małgorzata J. Zimoń, Robert Sawko, Ryan Tunstall, Charles Moulinec, David R. Emerson. 2019-11-12. Thermal transients in a U-Bend. https://doi.org/10.1016/j.ijheatmasstransfer.2019.119039

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