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000232314 001__ 232314 000232314 005__ 20180913064551.0 000232314 0247_ $$2doi$$a10.1017/jfm.2017.372 000232314 022__ $$a0022-1120 000232314 02470 $$2ISI$$a000411563700007 000232314 037__ $$aARTICLE 000232314 245__ $$aDirect numberical simulation of turbulent slope flows up to Grash of number Gr=2.1 x 10(11) 000232314 260__ $$aNew York$$bCambridge Univ Press$$c2017 000232314 269__ $$a2017 000232314 300__ $$a32 000232314 336__ $$aJournal Articles 000232314 520__ $$aStably stratified turbulent flows over an unbounded, smooth, planar sloping surface at high Grashof numbers are examined using direct numerical simulations ( DNS). Four sloping angles ( alpha = 15 degrees; 30 degrees; 60 degrees and 90 degrees) and three Grashof numbers (Gr = 5 X 10(10); 1 X 10(11) and 2 : 1 X 10(11)) are considered. Variations in mean flow, second- order statistics and budgets of mean- ( MKE) and turbulent- kinetic energy ( TKE) are evaluated as a function of ff and Gr at fixed molecular Prandtl number. Pr = 1 . Dynamic and energy identities are highlighted, which diagnose the convergence of the averaging operation applied to the DNS results. Turbulent anabatic ( upward moving warm fluid along the slope) and katabatic ( downward moving cold fluid along the slope) regimes are identical for the vertical wall set- up ( up to the sign of the along- slope velocity), but undergo a different transition in the mechanisms sustaining turbulence as the sloping angle decreases, resulting in stark differences at low ff. In addition, budget equations show how MKE is fed into the system through the imposed surface buoyancy, and turbulent fluctuations redistribute it from the low- level jet ( LLJ) nose towards the boundary and outer flow regions. Analysis of the TKE budget equation suggests a subdivision of the boundary layer of anabatic and katabatic flows into four distinct thermodynamical regions: ( i) an outer layer, corresponding approximately to the return flow region, where turbulent transport is the main source of TKE and balances dissipation; ( ii) an intermediate layer, bounded below by the LLJ and capped above by the outer layer, where the sum of shear and buoyant production overcomes dissipation, and where turbulent and pressure transport terms are a sink of TKE; ( iii) a buffer layer, located at 5 / z C / 30, where TKE is provided by turbulent and pressure transport terms, to balance viscous diffusion and dissipation; and ( iv) a laminar sublayer, corresponding to z C / 5, where the influence of viscosity is significant.. / C denotes a quantity rescaled in inner units. Interestingly, a zone of global backscatter ( energy transfer from the turbulent eddies to the mean flow) is consistently found in a thin layer below the LLJ in both anabatic and katabatic regimes. 000232314 6531_ $$aatmospheric flows 000232314 6531_ $$aboundary layer structure 000232314 6531_ $$ameteorology 000232314 700__ $$0246172$$aGiometto, M. G.$$g218957$$uUniv British Columbia, Dept Civil Engn, Vancouver, BC V6T 1Z4, Canada 000232314 700__ $$aKatul, G. G.$$uDuke Univ, Nicholas Sch Environm, Durham, NC 27708 USA 000232314 700__ $$0240839$$aFang, J.$$g133327$$uEcole Polytech Fed Lausanne, Sch Architecture Civil & Environm Engn, CH-1015 Lausanne, VD, Switzerland 000232314 700__ $$0242902$$aParlange, M. B.$$g155043$$uUniv British Columbia, Dept Civil Engn, Vancouver, BC V6T 1Z4, Canada 000232314 773__ $$j829$$q589-620$$tJournal Of Fluid Mechanics 000232314 909C0 $$0252105$$pEFLUM$$xU11028 000232314 909CO $$ooai:infoscience.tind.io:232314$$particle 000232314 937__ $$aEPFL-ARTICLE-232314 000232314 973__ $$aEPFL$$rREVIEWED$$sPUBLISHED 000232314 980__ $$aARTICLE