Large-eddy simulation of the lid-driven cubic cavity flow by the spectral element method

This paper presents the large-eddy simulation of the lid-driven cubic cavity flow by the spectral element method (SEM) using the dynamic model. Two spectral filtering techniques suitable for these simulations have been implemented. Numerical results for Reynolds number $\text{Re}=12'000$ are showing very good agreement with other experimental and DNS results found in the literature

Numerical studies towards practical large-eddy simulation

Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria: numerical qualities (precision and spectral characteristics), and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and "low-cost" shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine

Turbulent Compressible Convection with Rotation - Penetration above a Convection Zone

We perform Large eddy simulations of turbulent compressible convection in stellar-type convection zones by solving the Navi\'{e}r-Stokes equations in three dimensions. We estimate the extent of penetration into the stable layer above a stellar-type convection zone by varying the rotation rate ({\boldmath$\rm\Omega$}), the inclination of the rotation vector ($\theta$) and the relative stability ($S$) of the upper stable layer. The computational domain is a rectangular box in an f-plane configuration and is divided into two regions of unstable and stable stratification with the stable layer placed above the convectively unstable layer. Several models have been computed and the penetration distance into the stable layer above the convection zone is estimated by determining the position where time averaged kinetic energy flux has the first zero in the upper stable layer. The vertical grid spacing in all the model is non-uniform, and is less in the upper region so that the flows are better resolved in the region of interest. We find that the penetration distance increases as the rotation rate increases for the case when the rotation vector is aligned with the vertical axis. However, with the increase in the stability of the upper stable layer, the upward penetration distance decreases. Since we are not able to afford computations with finer resolution for all the models, we compute a number of models to see the effect of increased resolution on the upward penetration. In addition, we estimate the upper limit on the upward convective penetration from stellar convective cores.Comment: Accepted for Publication in Asttrophysics & Space Scienc

Impacts of cumulus convection parameterization on aqua-planet AGCM Simulations of tropical intraseasonal variability

Using an aqua-planet version of an atmospheric general circulation model (AGCM), the dependence of the tropical intraseasonal oscillation (ISO) simulation on the cumulus parameterization was examined with three different cumulus schemes-simplified Arakawa-Schubert, Kuo, and moist convective adjustment. The simulated intensity and propagation characteristics of the ISO depend significantly on the choice of cumulus scheme, in which more constrained convection scheme produces stronger intraseasonal variability in tropics. Mean thermodynamic state and the Intertropical Convergence Zone (ITCZ) structure also vary among the simulations, demonstrating that the ISO variability and the mean states are mutually dependent. Following Tokioka et al. (1988), the simplified Arakawa-Schubert scheme was modified by posing a minimum entrainment rate constraint for cumuli, and the relationship between tropical intraseasonal variability and zonal mean rainfall structure was examined. More constraining deep convections, the tropical ISO variability becomes stronger with narrower ITCZ structures. Vertical and horizontal structures of eastward propagating waves appeared in the aqua-planet experiments were further investigated. The vertical structures of propagating waves are consistent with observations of the Madden-Julian Oscillation, but the vertical profile of ISO-modulated heating exhibits a middle-heavy structure and the simulated waves show relatively faster propagations compared with the observed. The horizontal composite structures show the boundary-layer moisture frictional convergence to the east, and divergence to the west of the convective region, and this suggests that a frictional Kelvin wave-CISK mechanism is important to these eastward propagating waves.close635