A numerical study of atmospheric turbulence effects on wind-turbine wakes is presented. Large-eddy simulations of neutrally-stratified atmospheric boundary layer flows through stand-alone wind turbines were performed over homogeneous flat surfaces with four different aerodynamic roughness lengths. Emphasis is placed on the structure and characteristics of turbine wakes in the cases where the in...

Drift wave maps, area preserving maps that describe the motion of charged particles in drift waves, are derived. The maps allow the integration of particle orbits on the long time scale needed to describe transport. Calculations using the drift wave maps show that dramatic improvement in the particle confinement, in the presence of a given level and spectrum of E3B turbulence, can occur for q(r...

Whether or not a sediment particle is entrained from a channel bed is associated with both average bed shear stress and shear stress fluctuation, the latter being flow-dependent and also related to bed irregularities. In the first part of this study, a preliminary analysis of possible fluctuations induced by bed roughness is presented for the case of immobile plane bed comprised of unisized sed...

Turbulent flows are ubiquitous both in nature and in engineering applications, with far-reaching implications. Turbulence in wall bounded shear flows such as that in pipes, channels and boundary layers feature turbulent transition at Reynolds numbers for which the laminar flow is linearly stable [1], and often do so in the form of discrete patches of turbulence surrounded by quiescent fluid [2]...

Figure 1: Reynolds’ 1883 experiment, still operating at the University of Manchester, UK. Water flows down a long pipe and ink is introduced at the pipe centerline. On the right are the original drawings showing the dye filament in laminar flow (a), and the rapid mixing of the dye and water when the Reynolds number is larger than about 2000 in (b). (c) shows details of vortical structures in tu...

Motivated by recent experimental and numerical results, a simple unifying picture of intermittency in turbulent shear flows is suggested. Integral structure functions (ISF), taking into account explicitly the shear intensity, are introduced on phenomenological grounds. ISF can exhibit a universal scaling behavior, independent of the shear intensity. This picture is in satisfactory agreement wit...

A new non-local mechanism of the global confinement degradation and ion temperature profile stiffness is proposed based on the results of global gyrokinetic simulations. We find that turbulence spreading into a marginally stable zone can increase turbulent transport to a level exceeding the predictions of the local theories. Also, we present the first quantification of the parametric dependence...

According to our observation of turbulence generation, all small length scales are generated by shear layer instability. The size of small vortices should be determined by the smallest stable shear layer, e.g. smallest shear layer like laminar sub-layer in the wall bounded flow. This paper provides a new estimation of the smallest length scale by using the shear layer stability analysis, which ...

Recent observations show Heand N-enhancements in fast rotating O-type stars, while studies on shear mixing in rotating stars have shown that the μ-gradients generally inhibit mixing processes. However, these studies (including ours) ignored the other sources of turbulence, such as semiconvection and horizontal turbulence, which may be present in the medium and may modify the onset of shear mixi...