(221u) Accuracy Evaluation of Finite Volume Method based Direct Numerical Simulation for Solving Highly Turbulent Flows

Direct Numerical Simulation (DNS) has been carried out in the sub critical regime (Re = 10000) for the flow past a stationary sphere. The critical parameters affecting the accuracy of DNS lies in the degree of accuracy which ultimately is governed by two important parameters, the grid sizing and the temporal resolution. Moreover, for simulating unbounded free shear flows, the appropriateness of the boundary conditions, domain size and the discretization schemes also play an important role. Benchmark DNS of free shear flows using spectral or pseudo-spectral methods have been extensively carried out for low to moderate Re cases. The accuracy of these methods lies in their fundamental formulation which makes them the most favorable choice for DNS. However, these methods have still not been capable of simulating highly turbulent flows. Thus, there have been constant efforts to devise satisfactory methods for fully resolved simulations of high Re flows. Lately, the availability of high performance computing systems, it has been possible to obtain grid sizes of the order of Kolmogorov length scales even for highly turbulent flows. Although these meshes are not perfectly hexahedral, they have proven to be of adequate quality to simulate low to moderate Re flows using the FVM based solvers. In this study, we extend our previous investigation (which was limited to Re=1000) to fully resolve turbulent flows using FVM models. Extensive validation studies have been performed in the present work to evaluate the capability of FVM based discretization schemes for solving turbulent flows on polyhedral meshes. It has been found that with an appropriate combination of discretization schemes, grid sizing and time steps, it is possible to simulate fully resolved flows using FVM based DNS. The present investigation is a step towards our continuous effort of trying to simulate highly turbulent flows using FVM based DNS.

Keywords: Turbulence, energy spectra, discretization schemes, Direct Numerical Simulation.