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Weekly Seminar: Spring 2016

Speaker: Dr. Richard J.A.M. Stevens (University of Twente)
Winner of the 2015 Corrsin-Kovasznay Outstanding Paper Award

Title: "Challenging the large eddy simulation technique for turbulent wall-bounded flow with advanced a posteriori tests"
Hosted By: Charles Meneveau (ME)

Date: Friday, March 25, 2016
Time: 11:00 a.m.
Location: Gilman Hall 50 (Marjorie M. Fisher Hall)


Abstract

The logarithmic law for the mean velocity in turbulent boundary layers has long provided a valuable and robust reference for comparison with theories, models and large-eddy simulations (LES) of wall-bounded turbulence. More recently, analysis of high-Reynolds-number experimental boundary-layer data has shown that also the variance and higher-order moments of the streamwise velocity fluctuations u0C display logarithmic laws. Such experimental observations motivate the question whether LES can accurately reproduce the variance and the higher-order moments, in particular their logarithmic dependency on distance to the wall. In this study we perform LES of very high-Reynolds-number wall-modelled channel flow and focus on profiles of variance and higher-order moments of the streamwise velocity fluctuations. In agreement with the experimental data, we observe an approximately logarithmic law for the variance in the LES, with a ‘Townsend–Perry’ constant of A_1 \approx 1.25. The LES also yields approximate logarithmic laws for the higher-order moments of the streamwise velocity. Good agreement is found between Ap, the generalized ‘Townsend–Perry’ constants for moments of order 2p, from experiments and simulations. Both are indicative of sub-Gaussian behavior of the streamwise velocity fluctuations. The near-wall behavior of the variance, the ranges of validity of the logarithmic law and in particular possible dependencies on characteristic length scales such as the roughness length z_0, the LES grid scale \Delta, and subgrid scale mixing length Cs\Delta are examined. We also present LES results on moments of spanwise and wall-normal fluctuations of velocity.

Bio

Dr. Richard Stevens is a FOM YES! fellow at the University of Twente in the Netherlands where he works on the development of large eddy simulations (LES) for wind-farms. He previously worked on this topic with Prof. Charles Meneveau at the Johns Hopkins University. Stevens obtained his master (2008) and PhD (2011) degree cum laude in the group of Prof. Detlef Lohse at Twente University, where he worked on Rayleigh-Benard convection in collaboration with the group of Prof. Herman Clercx at Eindhoven University. He is co-author of over 40 published articles and received various Dutch and European awards for his PhD thesis. Recently, Dr. Richard Stevens received the "Corrsin-Kovasznay Outstanding Paper Award" who is lead author of a recent paper in fluid mechanics for the work's excellence, originality and potential impact for his paper “Large-eddy simulation study of the logarithmic law for second and higher-order moments in turbulent wall-bounded flow”, published in the Journal of Fluid Mechanics (volume 757, pages 888-907, with M. Wilczek and C. Meneveau).



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