The transitional boundary layer flow over a flat plate is investigated. The boundary layer flow is known to develop unstable Tollmien-Schlichting waves above a critical value of the Reynolds number. However, it is also known that this transition can be observed for sub-critical Reynolds numbers. In that case the basin of attraction of the laminar state coexists with the sustained turbulence. In...

This book has been awaited in the atmospheric boundary-layer research community for a long time. JohnWyngaard, the author of the book, is by all counts an outstanding figure in the area of atmospheric turbulence studies. His contributions to the field are both numerous and exceptional. As a person, John comprises all the principal qualities of an outstanding scientist and academic: curiosity, w...

In turbomachinery flows, the boundary-layer can remain laminar up to 70% of the chord length, due to a relatively low local Reynolds number on the blade. The high free-stream turbulence intensity penetrates into the laminar boundary-layer by the combined action of turbulence diffusion and pressure fluctuations, and triggers the transition process to a turbulent state. This transition process is...

The primary research goal is to develop techniques to determine subsurface turbulence from remote measurements using infrared imaging of the skin layer. We aim to infer flow rate, turbulence intensity and subsurface-generated turbulent structures from surface temperature patterns. We will take advantage of the two complementary indicators of subsurface flow provided by IR imagery: the thermal s...

Direct numerical simulation of turbulent homogeneous shear ow is performed in order to clarify compressibility e ects on the turbulence growth in the ow. The two Mach numbers relevant to homogeneous shear ow are the turbulent Mach number Mt and the gradient Mach number Mg . Two series of simulations are performed where the initial values of Mg and Mt are increased separately. The growth rate of...

Advances in the visualization and prediction of turbulence are shedding new light on mass transfer in the turbulent boundary layer. These discoveries have important implications for many topics in environmental science and engineering, from the transport of earth-warming CO2 across the sea-air interface, to nutrient processing and sediment erosion in rivers, lakes, and the ocean, to pollutant r...

The mechanism behind the collapse of turbulence in the evening as a precursor to the onset of the very stable boundary layer is investigated. To this end a cooled, pressure-driven flow is investigated by means of a local similarity model. Simulations reveal a temporary collapse of turbulence whenever the surface heat extraction, expressed in its nondimensional form h/L, exceeds a critical value...

The objective of this research is to improve the surface flux and boundary layer turbulence parameterization in COAMPS for lowand high-wind events over the ocean in the context of air-sea interaction. Special emphasis will be placed on flux parameterizations in low-wind regimes in collaboration with CBLAST DRI (Coupled Boundary Layer Layers/Air-Sea Transfer Defense Research Initiative) community.

A number of simplified dynamical problems is studied in an attempt to clarify some of the mechanisms leading to turbulence and the existing proposals to control this transition. A simplified set of boundary layer equations displays a solution that corresponds to the rolls and streaks instability and exhibits its streamwise localized nature. The effect of random phases as a device to control the...

The role of ground-based remote sensors in boundary-layer research is reviewed, emphasizing the contributions of radars, sodars, and lidars. The review begins with a brief comparison of the state of remote sensors in boundary-layer research 25 years ago with its present-day status. Next, a summary of the current capabilities of remote sensors for boundary-layer studies demonstrates that for bou...