Lab Home | Phone | Search
Center for Nonlinear Studies  Center for Nonlinear Studies
 Home 
 People 
 Current 
 Executive Committee 
 Postdocs 
 Visitors 
 Students 
 Research 
 Publications 
 Conferences 
 Workshops 
 Sponsorship 
 Talks 
 Seminars 
 Postdoc Seminars Archive 
 Quantum Lunch 
 Quantum Lunch Archive 
 P/T Colloquia 
 Archive 
 Ulam Scholar 
 
 Postdoc Nominations 
 Student Requests 
 Student Program 
 Visitor Requests 
 Description 
 Past Visitors 
 Services 
 General 
 
 History of CNLS 
 
 Maps, Directions 
 CNLS Office 
 T-Division 
 LANL 
 
Thursday, January 27, 2011
2:00 PM - 3:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Postdoc Seminar

Compressible Turbulence: Cascade, Locality, and Scaling

Hussein Aluie
T-5 and CNLS

Seventy years have passed since Kolmogorov's successful theory of incompressible turbulence, yet there is a stark absence of an analogous theory to describe compressible flows. I will briefly discuss the key notions of an inertial-range and the cascade in turbulence. I will present the relevant background and some of the difficulties that have prevented an extension of these concepts to compressible flows. I will then go over some recent developments in this regard. Some of my main conclusions which emerge from this work are: (1) any scale-decomposition aimed at probing inertial-range dynamics must satisfy an “inviscid criterion,” i.e. it must guarantee that viscous effects on the dynamics of large-scale flow are negligible. (2) The inviscid criterion naturally leads to a density-weighted coarse-graining of the velocity field. Such a coarse-graining method is already known in the literature as Favre filtering; however its use has been primarily motivated by appealing modelling properties rather than underlying physical considerations. (3) The non-linear transfer of kinetic energy to small scales is dominated by scale-local interactions. In particular, the results preclude transfer of kinetic energy from large-scales directly to dissipation scales, such as into shocks, in high Reynolds number turbulence as is commonly believed. (4) If the pressure dilatation co-spectrum decays fast enough, I will show that mean kinetic and internal energy budgets statistically decouple beyond a transitional ``conversion'' range. (5) In collaboration with Shengtai Li, Hui Li, and Hao Xu at LANL, we use high-resolution numerical simulations of forced and decaying compressible turbulence to compute, for the first time, pressure dilatation co-spectrum and verify statistical decoupling. (6) The analysis establishes the existence of an ensuing inertial range over which mean subgrid-scale (SGS) kinetic energy flux becomes constant, independent of scale. Over this inertial range, mean kinetic energy cascades locally and in a conservative fashion, despite not being an invariant. Time permitting, I will then discuss rigorous constraints on the scaling of density, velocity, and pressure spectra and structure functions.

Host: Peter Loxley, loxley@lanl.gov