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Turbulent natural convection in enclosure is a paradigmatic case for wide class of\ud processes of great interest for industrial and environmental problems.The solid-fluid\ud thermal interaction, the anisotropy of the turbulence intensity in the flow field along\ud with the transient nature of heat transfer processes, pose challenges regarding the\ud numerical modeling. The case of a square cavity with differently heated vertical\ud walls and two horizontal conductive plates is studied at Ra = 1.58 × 109. The study\ud is carried out numerically, using large-eddy simulation together with a dynamic\ud Lagrangian turbulence model and a conjugate heat transfer method to take into\ud account heat transfer at the solid surfaces. First, validation is carried out against the\ud literature experimental and numerical data. The results of validation tests evidence the\ud limitations of using the adiabatic conditions as a model for reproducing an insulator.\ud In fact, the adiabatic condition represents the asymptotic behavior which is often\ud difficult to reach in real conditions. Successively, the model is used to investigate the\ud effect on the flow field of different materials composing the horizontal walls. Initial\ud conditions representative of physical experiment are used. In order to reduce the\ud computational time required for a simulation with insulating materials at the walls,\ud a four-step temperature advancement strategy is proposed, based on the artificial\ud reduction-first and recover-later of the specific heat coefficient Cp of the materials\ud at different stages of the simulation. The conductivity of the solid media is found\ud to influence the flow configuration since heat transfer at the solid walls substantially\ud modifies the turbulent field and makes the flow field less homogeneous along the horizontal\ud direction

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Abstract. In the present paper a state-of-the-art large eddy simulation model (LES-COAST), suited for the analysis of water circulation and mixing in closed or semi-closed areas, is presented and applied to the study of the hydrodynamic characteristics of the Muggia bay, the industrial harbor of the city of Trieste, Italy. The model solves the non-hydrostatic, unsteady Navier-Stokes equations, under the Boussinesq approximation for temperature and salinity buoyancy effects, using a novel, two-eddy viscosity Smagorinsky model for the closure of the subgrid-scale momentum fluxes. The model employs: a simple and effective technique to take into account wind-stress inhomogeneity related to the blocking effect of emerged structures, which, in turn, can drive localscale, short-term pollutant dispersion; a new nesting procedure to reconstruct instantaneous, turbulent velocity components, temperature and salinity at the open boundaries of the domain using data coming from large-scale circulation models (LCM). Validation tests have shown that the model reproduces field measurement satisfactorily. The analysis of water circulation and mixing in the Muggia bay has been carried out under three typical breeze conditions. Water circulation has been shown to behave as in typical semi-closed basins, with an upper layer moving along the wind direction (apart from the anti-cyclonic veering associated with the Coriolis force) and a bottom layer, thicker and slower than the upper one, moving along the opposite direction. The study has shown that water vertical mixing in the bay is inhibited by a large level of stable stratification, mainly associated with vertical variation in salinity and, to a minor extent, with temperature variation along the water column. More intense mixing, quantified by sub-critical values of the gradient Richardson number, is present in near-coastal regions where upwelling/downwelling phenomena occur. The analysis of instantaneous fields has detected the presence of large crosssectional eddies spanning the whole water column and contributing to vertical mixing, associated with the presence of sub-surface horizontal turbulent structures. Analysis of water renewal within the bay shows that, under the typical breeze regimes considered in the study, the residence time of water in the bay is of the order of a few days. Finally, vertical eddy viscosity has been calculated and shown to vary by a couple of orders of magnitude along the water column, with larger values near the bottom surface where density stratification is smaller.

In the present paper we study buoyant (plume) and non-buoyant (jet) fluid injection in a neutrally stratified uniform cross-flow. Both cases are of practical importance in environmental fluid mechanics. The study is carried out numerically, using highly resolved large-eddy simulation in conjunction with the Lagrangian dynamic sub-grid scale model for both momentum and scalar transport equations. The velocity ratio is κ = 8. In the plume case, the Froude number is F = 10, such to allow the use of the Boussinesq approximation. The simulations are successfully validated against experimental data and well established semiempirical relations. The study shows the existence of three different regions as regards the plume evolution, each of them characterised by different peculiarities: in momentum-buoyancy region the plume exhibits an almost steady cylindrical shape with relative small turbulence structures; in deflection region the plume is deviated horizontally and a high shear rate is detected; in entrainment region the vortex pair develops, along with the sausage-like turbulent structure. The comparison between the plume and the jet case shows that the latter has a higher eccentricity while its trajectory height is sensibly lower. Also, the sausage-like structures are not present. Finally, an empirical formula for the jet trajectory is given, although its full validation will require additional studies. Keywords Large-eddy simulation • buoyant jet in cross-flow • turbulence structures • OpenFOAM.