Wind shear

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

Wind environmental conditions in passages between two long narrow perpendicular buildings

Abstract: This paper presents wind tunnel measurements of pedestrian wind conditions in passages between various configurations of two long narrow perpendicular buildings in open country exposure. The investigated parameters are passage width, building height and wind direction. The measurements were made along the passage centerline. The aim of the paper is to provide more insight in the pedestrian wind conditions in these basic building configurations, to address some contradictory statements reported in the literature and to provide detailed experimental data for Computational Fluid Dynamics (CFD) validation. The results show that the wind speed amplification factors in diverging passages are generally larger than in converging passages. It is also shown that the maximum wind speed amplification factors increase monotonically with decreasing passage width, contrary to some general building design guidelines proposed in the past for such building configurations. Significant issues concerning the use of the experimental data for CFD validation are also discussed. Subject headings: Wind tunnel test; Boundary layer flow; Turbulent flow; Buildings; Wind speed; Amplification; Computational Fluid Dynamics.

An investigation of the structure and dynamics of an intense surface frontal zone

Abstract: Intensive analysis of a pronounced surface frontal zone indicates that the associated horizontal temperature gradient, horizontal wind shear and horizontal divergence are most extreme near the ground and become much more diffuse above the lowest few thousand feet. In an endeavor to account for these structural characteristics, measurements are made of the frontogenetical and frontolytical effects in the fields of temperature and wind, following the motion of the air. In the vicinity of the frontal zone in the lowest levels, these effects are found to be one or two orders of magnitude larger than those generally observed in the free atmosphere. It is indicated that the frontal zone itself is composed of air initially in the warm sector which has been first effectively entrained into the zone through the operation of intense frontogenetical effects and is then subjected to intense frontolysis as it rises within the zone, thus accounting for the observed maximum intensity of the frontal characterist...

Markov chain simulations of vertical dispersion in the neutral surface layer for surface and elevated releases

Abstract: Vertical dispersion in the neutral surface layer is investigated using a Markov Chain simulation procedure. The conceptual basis of the procedure is discussed and computation procedures outlined. Wind and turbulence parameterizations appropriate to the neutral surface layer are considered with emphasis on the Lagrangian time scale. Computations for a surface release are compared with field data. Good agreement is found for the variation of surface concentration and cloud height to distances 500 m downwind of the source. The functional form of the vertical concentration profile is examined and an exponential with exponent ∼ 1.6 is found to give the best fit with simulations. For elevated releases, it is demonstrated that an initial dip of the mass mean height from the simulation can be normalized for various release heights using a non-dimensionalized downwind coordinate incorporating advective wind speed and wind shear. The vertical distribution standard deviation (σ z ), as employed in Gaussian models, shows a fair degree of independence with source height but close examination reveals an optimum source height for maximum σz at a given downwind distance,x. This source height increases with downwind distance. Also the simulations indicate that vertical wind shear is more important than vertical variation of Lagrangian time scale close to the source, with a reverse effect farther downwind.

Influence of Environmental Vertical Wind Shear on the Intensity of Hurricane-Strength Tropical Cyclones in the Australian Region

Abstract: NCEP–NCAR reanalyses have been used to investigate the impact of environmental wind shear on the intensity change of hurricane-strength tropical cyclones in the Australian region. A method of removing a symmetric vortex from objective analyses is used to isolate the environmental flow. A relationship between wind shear and intensity change is documented. Correlations between wind shear and intensity change to 36 h are of the order of 0.4. Typically a critical wind shear value of ∼10 m s−1 represents a change from intensification to dissipation. Wind shear values of less than ∼10 m s−1 favor intensification, with values between ∼2 and 4 m s−1 favoring rapid intensification. Shear values greater than ∼10 m s−1 are associated with weakening, with values greater than 12 m s−1 favoring rapid weakening. There appears to be a time lag between the onset of increased vertical wind shear and the onset of weakening, typically between 12 and 36 h. A review of synoptic patterns during intensification-weakenin...

Volumetric Lidar Scanning of Wind Turbine Wakes under Convective and Neutral Atmospheric Stability Regimes

Abstract: Optimization of a wind farm’s layout is a strategic task to reduce wake effects on downstream turbines, thus maximizing wind power harvesting. However, downstream evolution and recovery of each wind turbine wake are strongly affected by the characteristics of the incoming atmospheric boundary layer (ABL) flow, such as the vertical profiles of the mean wind velocity and the turbulence intensity, which are in turn affected by the ABL thermal stability. Therefore, the characterization of the variability of wind turbine wakes under different ABL stability regimes becomes fundamental to better predict wind power harvesting and to improve wind farm efficiency. To this aim, wind velocity measurements of the wake produced by a 2-MW Enercon E-70 wind turbine were performed with three scanning Doppler wind lidars. One lidar was devoted to the characterization of the incoming wind—in particular, wind velocity, shear, and turbulence intensity at the height of the rotor disc. The other two lidars performed vol...