A class of subgrid stress ~SGS! models for large-eddy simulation ~LES! is presented based on the idea of structure-based Reynolds-stress closure. The subgrid structure of the turbulence is assumed to consist of stretched vortices whose orientations are determined by the resolved velocity field. An equation which relates the subgrid stress to the structure orientation and the subgrid kinetic ene...

This paper summarises some of the recent progress that has been made in understanding astrophysical plasma turbulence in the solar wind, from in situ spacecraft observations. At large scales, where the turbulence is predominantly Alfvénic, measurements of critical balance, residual energy and three-dimensional structure are discussed, along with comparison to recent models of strong Alfvénic tu...

In my thesis I study two different models of turbulence. The first part of my research concerns the, so-called, shell models of turbulence. Shell models had attracted a lot of interest as useful phenomenological models that mimics certain features of the Navier-Stokes equations (NSE). The shell models capture different aspects of the real turbulent flows, such as the energy cascade, an anomalou...

The turbulent flow in a tangential inlet / tangential outlet vortex tube is numerically simulated using a modified   k turbulence model. The results are compared to experimental measurements from literature. The modified model shows better agreement with the local tangential velocity measurements compared to the standard and RNG   k turbulence models. The flow structure is also demonstrated...

Atmospheric turbulence has significant influences on both the trajectories and strengths of wake vortices. In this paper, a quasi-wavelet method is used to generate a random atmospheric turbulence field based on the von Kármán spectrum, in which atmospheric turbulence is represented by groups of random eddies. An inviscid wake vortex system, out-of-ground effect or in-ground effect, is immersed...

As part of a more general program of developing multiple-scale models of turbulence, Schiestel suggested a derivation of the homogeneous part of the dissipation rate transport equation. Schiestel's approach is generalized to rotating turbulence. The resulting model reproduces the main features observed in decaying rotating turbulence.