Anikesh Pal

ALE–VMS formulation for stratified turbulent incompressible flows with applications

A numerical formulation for incompressible flows with stable stratification is developed using the framework of variational multiscale methods. In the proposed formulation, both density and temperature stratification are handled in a unified manner. The formulation is augmented with weakly-enforced essential boundary conditions and is suitable for applications involving moving domains, such as fluid–structure interaction. The methodology is tested using three numerical examples ranging from flow-physics benchmarks to a simulation of a full-scale offshore wind-turbine rotor spinning inside an atmospheric boundary layer. Good agreement is achieved with experimental and computational results reported by other researchers. The wind-turbine rotor simulation shows that flow stratification has a strong influence on the dynamic rotor thrust and torque loads.

The spatial evolution of fluctuations in a self-propelled wake compared to a patch of turbulence

The primary focus of this study is to contrast the influence of the mean velocity profile with that of the initial turbulence on the subsequent evolution of velocity and density fluctuations in a stratified wake. Direct numerical simulation is used to simulate the following cases: (a) a self-propelled momentumless turbulent wake, case SP50 with a canonical mean velocity profile, (b) a patch of turbulence, case TP1 with the same initial energy spectrum as (a), and (c) a patch of turbulence, case TP2 with a different initial energy spectrum with higher small-scale content. The evolution of the fluctuations is found to be strongly dependent on the initial energy spectrum, e.g., in case TP2, the kinetic energy is substantially smaller, and the late-wake vortices are less organized. The effect of the mean velocity field is negligible for mean kinetic energy (MKE) of the order 10% of the total kinetic energy and the evolution in this case is similar to a turbulent patch with the same initial energy spectrum. In...

On the vortex dynamics of flow past a sphere at Re = 3700 in a uniformly stratified fluid

Vortex dynamics in the flow past a sphere in a linearly stratified environment is investigated numerically. Simulations are carried out for a flow with Reynolds number of Re = 3700 and for several Froude numbers ranging from the unstratified case with Fr=∞ to a highly stratified wake with Fr = 0.025. Isosurface of Q criterion is used to elucidate stratification effects on vortical structures near the sphere and in the wake. Vortical structures in the unstratified case are tube-like and show no preference in their orientation. Moderate stratification alters the orientation of vortical structures to streamwise preference but does not change their tube-like form. In strongly stratified cases with Fr≤0.5, there is strong suppression in vertical motion so that isotropically oriented vortex tubes of approximately circular cross section are replaced by flattened vortex tubes that are horizontally oriented. At Fr = 0.025, pancake eddies and surfboard-like inclined structures emerge in the near wake and have a reg...