NUMERICAL ANALYSIS OF LARGE SCALE STRATIFIED FLOWS AROUND AN HORIZONTAL STRIP M. Riahi Khalloufi 1 H. Houcine 1 , P. Fraunie 2 , Y. D. Chashechkin 3 , A. Gharbi 1 1 Laboratoire de Mécanique des Fluides, Faculté des Sciences de Tunis, Université El Manar, 2092 Tunis, Tunisie 2 Université de Toulon, Aix-Marseille Université, CNRS/INSU, IRD, MIO, UM 110, 83957, La Garde Cedex, France 3 Institute for Problems in Mechanics of the Russian Academy of Sciences, Moscow, Russia, chakin@ipmnet.ru Abstract A numerical investigation of the stratified flow developing around a thin horizontal plate at moderate Reynolds numbers is presented. Direct numerical simulations or Large eddy simulations based on the JETLES numerical code are compared to linearized analytical solution concerning large scale structure of the flow. Key words: Stratified flows, Large eddy simulation, Internal waves, Wakes. 1 Introduction The density stratification has been investigated during last years as an important topic in environmental and technological flows. Density changes lead to specific set of phenomena, especially internal and lee waves and anisotropic turbulence due to inhibition of vertical mixing by stratification [1]. A numerical model adapted from the JETLES code [2] has been developed and validated [3]-[6] from laboratory experiments [7]-[8] performed in a salty water channel at low Reynolds number exhibiting reasonable agreement with data of Schlieren visualization, density marker and probe measurements of internal wave fields. In continuation to previous work concerning a vertical strip towed in a channel, new numerical results are presented for the more delicate case of horizontal plate. In this approach, the large scale structure of the flow is compared to a previous derived analytical solution [9] when the fine structure of the flow as introduced in [10] and occurring at high Reynolds numbers are presented in a companion paper (Y.D. Chashchkin & I.V. Zagumenny, same issue). 2 Numerical tools In this investigation, uniform flow of a stratified fluid with density profile ρ(z), of horizontal velocity U and buoyancy frequency z g N d dρ ρ = past a body of characteristic dimension D is considered (equivalent to a body moving with the same speed in opposite direction in a quiescent stratified fluid). The major dimensionless parameters governing this problem are the Froude Number ND U Fr = the Reynolds number ν UD = Re and ratio of intrinsic length scales D C Λ = (where       = z d ln d ρ Λ is a stratification length scale). Ratio of dissipative coefficients defines the Schmidt number S κ ν = Sc ( ν is kinematic viscosity and S κ is salt diffusivity). The set of the dimensionless parameters provide conditions of numeric and small scale laboratory modeling of environmental flows. The numerical code used herein was adapted [3-5] from the JETLES solver (courtesy of Verzicco and Orlandi [2]) to variable density flows. The second order finite difference discretization in combination with a third order Runge Kutta time marching procedure is quite efficient for fast unsteady flows at a reasonable computational cost. The 3D code has been rewritten in Cartesian mesh and equation of salinity transport has been added to account for density effects. The mean flow is assumed two dimensional, as TOPICAL PROBLEMS OF FLUID MECHANICS 191 _______________________________________________________________________ DOI: http://dx.doi.org/10.14311/TPFM.2016.026