Reduced-Order Modeling of Laminar-Turbulent Transition in Large-Eddy Simulations

Speaker: Philipp Hack, Center for Turbulence Research, Stanford University
May 9, 2019

Presentation

Abstract

The modeling of the laminar region and the prediction of the onset of transition remain key challenges in the numerical simulation of boundary layers. The issue is of particular relevance in wall-modeled large eddy simulations which require 10 to 100 times higher grid resolution in the thin laminar boundary layer than in the turbulent regime (Slotnick et al., NASA/CR-2014-218178, 2014). This talk examines the potential of the nonlinear parabolized stability equations (PSE) to provide an accurate, yet computationally efficient treatment of the growth of disturbances in the pre-transitional flow regime. The PSE capture the nonlinear interactions that eventually induce breakdown to turbulence, and can as such identify the onset of transition without relying on empirical correlations. Since the local PSE solution at the onset of transition is an approximate solution of the Navier-Stokes equations, it provides a natural inflow condition for large-eddy and direct simulations and avoids unphysical transients. Application to classical H-type transition scenario shows that a combined PSE/LES approach can closely reproduce the skin-friction distribution obtained in reference DNS while reducing computational cost by several orders of magnitude. The talk concludes with an outlook on the modeling of bypass transition and a new framework under development which seeks to overcome critical limitations of the PSE.

Biography

Philipp Hack is a research associate at the Center for Turbulence Research at Stanford University. His computational and theoretical work on the stability of shear flows was awarded in 2013 with the EPSRC Doctoral Prize Fellowship and in 2015 with a DFG Research Fellowship. Philipp Hack joined the group of Parviz Moin at the beginning of 2015 after receiving his Ph.D. from Imperial College London in 2014. His current research interests include flow instability, optimization, and reduced-order modeling.

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