Wind shear

About: Wind shear is a research topic. Over the lifetime, 8023 publications have been published within this topic receiving 185373 citations.

Relationship of oceanic whitecap coverage to wind speed and wind history

Abstract: Sea surface images obtained during the 2006 Marine Aerosol Production (MAP) campaign in the North East Atlantic were analysed for values of percentage whitecap coverage (W). Values of W are presented for wind speeds up to circa 23 m s-1. The W data were divided into two overlapping groups and a piecewise, wind-speed-only parameterization of W is proposed that is valid for wind speeds between 3.70 m s-1 and 23.09 m s-1. Segregation of data points based upon a 2.5 hour wind history acted to decrease data scatter at wind speeds above approximately 9.25 m s-1. At these wind speeds W values were greater for decreasing wind speeds than for increasing wind speeds. No clear wind history effect was observed at wind speeds below 9.25 m s-1. Copyright 2008 by the American Geophysical Union.

Modification of mean flow and turbulent energy by a change in surface roughness under conditions of neutral stability

Abstract: A theory is developed which describes the adjustment of the flow of a hydrostatically neutral fluid in the lower portion of a fully-turbulent boundary layer, after an abrupt change in surface roughness. The model is based on the hypothesis that the horizontal shear stress is proportional to the turbulent energy. The theory postulates that the flow is primarily governed by the dominant terms of the horizontal-momentum, continuity, and turbulent-energy equations. The model was solved by numerical techniques on a digital computer. Unlike previous models there are no a priori assumptions about the distribution of velocity or stress, the behaviour of the nondimensional wind shear, mixing length, or momentum-exchange coefficient in the transition region. The theory, in contrast to earlier theories, suggests the distribution of turbulent energy, as well as velocity. An inflection point is predicted in the transition velocity-profile. The nondimensional wind shear is found to differ significantly from unity in the transition region. These predictions agree with observation.

Atmospheric turbulence and its influence on the alternating loads on wind turbines

Abstract: Analysis of measurements on atmospheric turbulence with respect to the statistics of velocity increments reveals that the statistics are not Gaussian but highly intermittent. Here, we demonstrate that the higher quantity of extreme events in atmospheric wind fields transfers to alternating loads on the airfoil and on the main shaft in the form of torque fluctuations. For this purpose, alternating loads are discussed with respect to their increment statistics. Our conjecture is that the anomalous wind statistics are responsible for load changes, which may potentially contribute to additional loads and may cause additional fatigue. Our analysis is performed on three different wind field data sets: measured fields, data generated by a standard wind field model and data generated by an alternative model based on continuous time random walks, which grasps the intermittent structure of atmospheric turbulence in a better way. Our findings suggest that fluctuations in the loads might not be reflected properly by the standard wind field models.

Thunderstorm Initiation, Organization, and Lifetime Associated with Florida Boundary Layer Convergence Lines

Abstract: The initiation, organization, and longevity of thunderstorms associated with boundary layer convergence lines in the Cape Canaveral, Florida, vicinity are examined using data from the Convection and Precipitation/Electrification (CaPE) experiment. The project was conducted during July and August 1991 under low vertical wind shear situations. This observational study is based on Doppler radar, mesonet, balloon sounding, and satellite data. The primary convergence lines studied were the east coast sea-breeze front (ECSBF) and a frequently occurring gust front from the west termed the west coast front (WCF) that originates with storms initiated by the west coast sea-breeze front. Significantly fewer storms were associated with the ECSBF in comparison to the WCF. This was because the convergence with the ECSBF was shallower and weaker and the updrafts were shallow and tilted. The environmental winds were generally westerly near the top of the ECSBF and at storm steering level. As a result, the low-le...