| The objective of the present research was to investigate the applicability of large-eddy simulations to predict the characteristics of turbulent wakes of bluff bodies. The problem considered concerns turbulent flow over a square cylinder placed normal to a uniform free stream. The Reynolds number selected for the simulations is 21,400 where detailed experimental data are available. The computation times required for such simulations are quite large because of the fine grids and the large number of time steps that are necessary. Therefore, these calculations have been performed on massively parallel processing computers. The governing equations are approximated by a finite-volume discretization. Several alternate interpolation schemes, including a third-order (QUICK), a fifth-order, and a seventh-order upwinding-biased scheme, have been employed for convection terms. A data-parallel algorithm has been developed on the CM-5 machine, and its performance has been evaluated on various grid sizes in model flow problems and for different partition sizes.; For turbulent flow over a square cylinder, the turbulence evolves gradually with the downstream distance with varying energy spectra and small scale content. The dynamic sub-grid scale model can provide a good spatial distribution of the eddy viscosity as the computed Smagorinsky coefficient varies with time and space. Several calculations with progressive improvement in numerical accuracy and grid resolution have been conducted. The calculated integral parameters and time-averaged profiles of velocities and Reynolds stresses have been compared with the experimental data. Good agreement has been observed in several of the quantities compared, although further improvement is desirable. Further, we have presented some fundamental aspects of the large-scale flow characteristics. We have studied the low-frequency flapping phenomenon which is observed in the auto-correlations and the energy spectra of the fluctuating velocities. We have also presented two-dimensional and three-dimensional vortical structures, and the phase-averaged quantities which have been compared qualitatively with the experiments. |
