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Scaling of velocity fluctuations in statistically unstable boundary-layer flows

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  • Xiang I. A. Yang, Penn State University, PA
  • ,
  • Sergio Pirozzoli, University of Rome La Sapienza
  • ,
  • Mahdi Abkar

Much of our theoretical understanding of statistically stable and unstable flows is from the classical Monin-Obukhov similarity theory: The theory predicts the scaling of the mean flow well, but its prediction of the turbulent fluctuation is far from satisfactory. This study builds on Monin-Obukhov similarity theory and Townsend's attached-eddy hypothesis. We present a model that connects the mean flow and the streamwise velocity fluctuations in both neutral and unstable boundary-layer flows at both moderate and high Reynolds numbers. The model predictions are compared to direct numerical simulations of weakly unstable boundary layers at moderate Reynolds numbers, and large-eddy simulations of unstable boundary-layer flows at high Reynolds numbers. The flow is shear dominated. The range of stability parameter considered in this work is <![CDATA[$L/\unicode[STIX]{x1D6FF}, where is the Monin-Obukhov length, and is the boundary-layer height. Reasonably good prediction of velocity fluctuations based on knowledge of the mean velocity profile is obtained.

TidsskriftJournal of Fluid Mechanics
Antal sider19
StatusUdgivet - 10 mar. 2020

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