D. Tordella

F. De Santi

J. Riley

English

DE SANTI, FRANCESCA

TORDELLA, Daniela

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)

04 August 2020POLITECNICO DI TORINORepository ISTITUZIONALETwo-dimensional shearless turbulent mixing: kinetic energy selfdiffusion, also in the presence of a stable stratification / F.De Santi; D. Tordella; J. Riley. - STAMPA. - 5(2011), pp. 14-14. ((Intervento presentato al convegno 5th EuropeanPostgraduate Fluid Dynamics Conference tenutosi a Gottingen, Germany nel August, 9-12, 2011.OriginalTwo-dimensional shearless turbulent mixing: kinetic energy selfdiffusion, also in the presence of a stablestratificationPublisher:PublishedDOI:Terms of use:openAccessPublisher copyright(Article begins on next page)This article is made available under terms and conditions as specified in the  corresponding bibliographic description inthe repositoryAvailability:This version is available at: 11583/2447776 since:DLR Institute of Aerodyamics and Flow Technology5th European Postgraduate Fluid Dynamics ConferenceGöttingen, Germany9-12 August 2011Two-dimensional shearless turbulent mixing: kinetic energy selfdiffusion, also in the presence of a stable stratificationF. De Santi1, L. Ducasse1, J. Riley2, D. Tordella11Dipartimento di Ingegneria Aeronautica e Spaziale, Politecnico di Torino, Italy2Mechanical Engineering Department, University of Washington, WATwo-dimensional turbulence is important in many natural and engineering contexts. It presents some special and interest-ing phenomena that does not occur in three dimensional turbulence. Moreover, it also idealizes geophysical phenomena inthe atmosphere, oceans and magnetosphere and provides a starting point for the modeling of these phenomena [1, 2, 3, 4].In this contest, we would like to present new results concerning the turbulent energy transport in the simplest kind oftwo dimensional inhomogeneous flow, a turbulent shearless mixing process generated by the interaction of two isotropicturbulent fields with different kinetic energy but the same spectrum shape [5]. The self diffusion of kinetic energy isobserved in two cases: with and without a stable density stratification.In the unstratified case the simulations of mixing with different values of the energy ratio show that, asymptotically in time(in the limit of the observed range), the turbulent diffusion is much larger than the one measured in three dimensions[6, 7],see the full time history in the movie. The analysis of velocity third and fourth moments indicates that the flow is highlyintermittent. Moreover, the temporal autocorrelation of the vorticity, at some fixed points, does not depend on the ratio ofenergy used and on the position. We can interpret this results in term of the existence of a long-range interaction.In the stratified case the evolution of the flow changes significantly [8, 9]. The energy profile in the mixing region is lowerthan the minimum value imposed by the initial condition, which shows the effect of the buoyancy force work. Finally,the velocity skewness enlightens the generation of an inverse energy flow and intermittent penetration from the low to thehigh energy field even in the case of mild stratification.References[1] Davidson, P.A.: An introduction to magnetohydrodynamics, Cambridge university press, 1988[2] Kundu, P. and Cohen, I.:Fluid Mechanics, Academic press, 2002[3] Tritton, D.J.: Physical fluid dynamics, Oxford science publications, 2006[4] Kellay, H. and Goldburg, W.: Two-dimensional turbulence: a review of some recent experiment, Rep. Prog. Phys.,2002, vol. 65, 845-894[5] Veeravalli, S., and Warhaft, Z.: The shearless turbulence mixing layer, J. Fluid. Mech., 1989, vol.207, 191-229[6] Tordella, D. and Iovieno, M. and Bailey, P.R.: Sufficient condition for Gaussian departure in turbulence, Phys.Rev.,2008, vol.77[7] Tordella, D. and Iovieno, M.: Numerical experiments on the intermediate asymptotic of shear-free turbulent transportand diffusion, J.Fluid Mech., 2006, vol. 549, 429-441[8] Riley, J. and Lelong, M.P.: Fluid Motions in the presence of strong stable stratification,Ann. Rev. Fluid Mech., 2000,vol. 32, 617-657[9] Riley, J. and deBruynKops, S.M.: Dynamics of turbulence strongly influenced by buoyancy, Phys. Fluids, 2003, vol.15, 2047-2059[10] Tordella, D., Iovieno M.: Small scale anisotropy in the turbulent shearless mixing. Under revision for Phys. Rev.Lett., 2011.1

Two-dimensional shearless turbulent mixing: kinetic energy selfdiffusion, also in the presence of a stable stratification

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Two-dimensional shearless turbulent mixing: kinetic energy selfdiffusion, also in the presence of a stable stratification

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