Abstract:
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The incompressible Navier-Stokes equations constitute an excellent mathematical
modelization of turbulence. Unfortunately, attempts at performing direct simulations are
limited to relatively low-Reynolds numbers because of the almost numberless small scales
produced by the non-linear convective term. Alternatively, a dynamically less complex
formulation is proposed here. Namely, regularizations of the Navier-Stokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive terms are altered in the same vein. In this way, the convective production of small scales
is effectively restrained whereas the modified diffusive term introduces a hyperviscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient
is a self-adjoint linear filter whose local filter length is determined from the requirement that vortex-stretching must stop at the smallest grid scale. In the present work, the performance of the above-mentioned recent improvements is assessed through application to turbulent natural
convection flows by means of comparison with DNS reference data. |