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This study represents a comprehensive analysis of the wind climatology for the Toronto area based on the daily National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis 1 data extracted for the period 1948-2014. The research is focused on investigating wind speed and wind direction distributions, long-term wind trends, and low-frequency wind spectrum. The results are given at the sigma-995 level. Westerlies are active in about 50% of the time in year. The strongest winds are coming in from 240° direction and the windiest seasons are winter and fall, followed by spring. A trend analysis shows that statistically significant and positive wind speed trends are present for both the omnidirectional mean annual wind speeds as well as for the winds associated with the most prevailing wind directions. Winter and fall winds had positive trends whereas negative wind speed trends in the summer and spring seasons are negligible. The spectral analysis of wind speed time series shows three distinguished peaks: (1) 2-4.5 days, (2) yearly, and (3) 11-year peak. The lowest frequency peak in the wind speed spectra is linked to the solar activity through the cross-correlation analysis and the relationship is discussed in details. [ABSTRACT FROM AUTHOR]

An experimental study is conducted to investigate the flow dynamics within the near-wake region of a horizontal axis wind turbine using particle image velocimetry (PIV). Measurements were performed in the horizontal plane in a row of four radially distributed measurement windows (tiles), which are then patched together to obtain larger measurement field. The mean and turbulent components of the flow field were measured at various blade phase angles. The mean velocity and turbulence characteristics show high dependency on the blade phase angle in the near-wake region closer to the blade tip and become phase independent further downstream at a distance of about one rotor diameter. In the near-wake region, both the mean and turbulent characteristics show a systemic variation with the phase angle in the blade tip region, where the highest levels of turbulence are observed. The streamlines of the instantaneous velocity field at a given phase allowed to track a tip vortex which showed wandering trend. The tip vortices are mostly formed at r/ R > 1, which indicates the wake expansion. Results also show the gradual movement of the vortex region in the axial direction, which can be attributed to the dynamics of the helical tip vortices which after being generated from the tip, rotate with respect to the blade and move in the axial direction because of the axial momentum of the flow. The axial velocity deficit was compared with other laboratory and field measurements. The comparison shows qualitative similarity. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An inviscid tornadolike vortex is analytically modeled using a free narrow jet solution combined with a modified Rankine vortex. An empirical and simplified solution to existing models is defined for flows similar to the ones simulated in Ward-type vortex chambers. Velocity profiles are calculated for a particular swirl ratio Sr=0.28. The model shows reasonable agreement with existing experimental measurements by Baker (1981, "Boundary Layers in Laminar Vortex Flows," Ph.D. thesis, Purdue University, West Lafayette, IN) and the numerical simulation by Wilson and Rotunno (1986, "Numerical Simulation of a Laminar End-Wall Vortex and Boundary Layer," Phys. Fluids, 29(12), pp. 3993-4005). [ABSTRACT FROM AUTHOR]

Various types of impinging jet flows are analytically modeled using inviscid free Gaussian jet solutions superimposed with experimentally fitted boundary layer models. Improved (more robust) and simplified solutions to existing models are defined. Velocity profiles, surface pressure distributions, and streamline plots are calculated for circular, plane, and annular impinging jets. The models show excellent agreement with existing experimental results in both laminar and turbulent conditions and for different Reynolds numbers. [ABSTRACT FROM AUTHOR]

Downbursts are transient phenomena that produce wind profiles that are distinctly different from synoptic boundary layers. Wind field data from Computational Fluid Dynamics (CFD) simulations of isolated downburst-like impinging jets, are used to investigate structural loads of tall buildings due to these high intensity winds. The base shear forces and base moments of tall buildings of heights between 120 and 250 m produced by downburst winds of various scales are compared with the forces from the equivalent boundary layer gust winds, with matched 10-metre wind velocity. The wind profiles are mainly functions of the size of the downburst and the radial distance from the centre of the storm. Wind forces due to various downburst profiles are investigated by placing the building at different locations relative to the storm center as well as varying the size of the downburst. Overall it is found that downbursts larger than approx. 2,000m in diameter might produce governing design wind loads above those from corresponding boundary layer winds for tall buildings. [ABSTRACT FROM AUTHOR]

The high Reynolds number wake topology of a square prism is experimentally investigated using wavelet analysis. It is shown that a systematic application of one-dimensional continuous wavelet techniques, including a relatively new wavelet pattern recognition technique can reveal important three-dimensional features of the flow, assessing the validity of previously proposed wake topological models. Present results suggest that the high Reynolds number turbulent wakes are topologically similar, but not identical, to their laminar counterparts. [ABSTRACT FROM AUTHOR]

Characteristics of turbulent flow over a steep escarpment were studied using a 1:25 scale model of the Bolund hill in a wind tunnel under neutral atmospheric stability conditions. The influence of Reynolds number, inflow shear profile, and escarpment geometry were investigated in relation to flow behavior including separation and reattachment, Reynolds stresses, vorticity, Turbulent Kinetic Energy (TKE) production, and Gaussianity. Multi-camera Particle Image Velocimetry (PIV) was used to examine the flow in the vicinity of the escarpment leading edge. Four test cases were studied across a Reynolds number range of 1 × 10 5 < R e h < 5 × 10 5. Two different inflow profiles were evaluated, as well as two different leading edge geometries – a round edge with non-dimensional radius of curvature a η ≈ 0.2 and a sharp edge with η ≈ 0. A sharp leading edge was found to produce a well-defined separation bubble, yielding distributions and magnitudes of Reynolds stress, vorticity and TKE production closely resembling those of flow over an idealized forward facing step, as well as full-scale measurements of TKE. Gaussianity of the flow was significantly modified by the escarpment, with high skewness and kurtosis occurring in the sharp edge case along the boundary of the separation bubble. • Small changes in escarpment leading edge sharpness greatly influence turbulent flow behavior. • Sharp edge caused relocation of area of peak turbulent kinetic energy. • Turbulent flow of sharp edge case better approximated full-scale measurements. • Turbulent flow of sharp edge case similar to canonical forward-facing step. • Gaussianity modified along separation bubble boundary. [ABSTRACT FROM AUTHOR]

This article focuses on experimental investigation of the interaction between downburst (DB) and near-surface atmospheric boundary layer (ABL) winds. The flow field of DB immersed into ABL winds (DBABL) is compared against the outflow produced by an isolated DB without ABL winds. The diameter of investigated downdrafts was 3.2 ​m. The study demonstrates that there is a profound difference between the radial velocity components in the DBABL and DB outflows in terms of peak and mean velocities, vertical profile of radial velocity, as well as the overall temporal signature of the velocity records. The asymmetry of the DBABL outflow in the along-ABL wind direction is similar to that observed in real traveling downbursts. The turbulence intensity in the near-surface DBABL winds can exceed 40% in some parts of the outflow where the downburst propagates against ABL winds. The DBABL wind profile is characterized by smaller nose-shape curvature than the DB winds in the part of the outflow where downburst and ABL winds have the same direction. The steady-state ABL wind segments and transient downburst segments in the DBABL velocity records are similar to anemometer records of real downbursts. The paper also shows that the velocity addition DBABL → ≠ DB → + ABL → throughout the outflow. Image 1 • Unique physical experiments of a downburst outflow in ABL winds. • Substantial difference found between downburst outflows with and without ABL winds. • A good resemblance between physical experiments and full-scale data. • A conceptual model of downburst outflow in ABL winds proposed. • Vector addition of downburst outflow and ABL winds addressed. [ABSTRACT FROM AUTHOR]

Large eddy simulations (LES) of "tornado-like" vortices (TLVs) for a range of swirl ratios and surface roughness were conducted. The mean axial velocity distribution was used to identify a region of predominantly horizontal flow. An examination of the boundary layer within this inflow region was conducted with the primary objective of applying the traditional understanding of atmospheric boundary layer (ABL) to TLV boundary layer. A comparison with the boundary layer development over a flat plate revealed that the tornado boundary layer can be divided into a region of zero and favourable pressure gradient. Furthermore, the mean measures of the boundary layer in TLVs like the BL depth, displacement thickness, and momentum thickness were observed to be dependent on the external swirl ratio, ground roughness, and streamwise distance. The turbulent stresses, friction velocity and the aerodynamic roughness length in the TLV boundary layer were also observed to depend on the streamwise distance, indicating a lack of equilibrium due to a short fetch. ESDU predicted turbulence intensities, based on a crude comparison, were observed to be conservative for the lateral and vertical directions but under-conservative for the longitudinal component in regions marked by high aerodynamic roughness length. • LES of TLVs for different swirl ratio and ground roughness are carried out. • The inflow region, with predominantly horizontal flow, in the domain is identified. • The boundary layer characteristics are investigated and compared with straight-line flows. • Regions of zero and favourable pressure gradients in the boundary layer are identified. • The TLV boundary layer characteristics are functions of streamwise distance, ground roughness and external swirl ratio. [ABSTRACT FROM AUTHOR]

The traditional Davenport Chain method, which is at the base of current wind engineering practice, is founded on the assumption that engineering structures are subjected to loads resulting from their interaction with synoptic winds approximated by atmospheric boundary layer (ABL) flow fields. Herein, we introduce a new class of non-synoptic winds and bring forward the differences between the two wind systems in terms of climatology, microclimatology due to the surface layer characteristics, aerodynamic loading, and structural responses. We use a set of downburst and tornado simulations conducted during the last couple of years in the Wind Engineering, Energy and Environment (WindEEE) Dome at Western University, Canada to investigate and illustrate these differences. We show ways in which geometric, kinematic and dynamic scaling can be defined for the non-synoptic wind systems. In the process, we analyze the assumptions related to the quasi-steady theory, which is at the base of the Davenport Chain for ABL winds. We then interrogate the applicability of these assumptions to the non-synoptic – three-dimensional, non-stationary and non-Gaussian (3D-NS-NG) – wind systems, such as tornadoes and downburst, and their actions on buildings and structures. • Adaptation of Davenport Chain to non-synoptic winds. • Properties of three-dimensional, non-stationary, and non-Gaussian winds. • Climatology, Surface layer, Building aerodynamics effects. • Simulation and scaling of non-synoptic winds. [ABSTRACT FROM AUTHOR]

Snow accumulation on surfaces exposed to adverse weather conditions has been studied over the years due to a variety of problems observed in different industry sectors, such as aeronautics and wind and civil engineering. With the growing interest in autonomous vehicles (AVs), this concern extends to advanced driver-assistance systems (ADAS). Weather stressors, such as snow and icing, negatively influence the sensor functionality of AVs, and their autonomy is not guaranteed by manufacturers during episodes of intense weather precipitation. As a basis for mitigating the negative effects caused by heavy snowfall, models need to be developed to predict snow accumulation over critical surfaces of AVs. The present work proposes a framework for the study of snow accumulation on road vehicles. Existing icing and snow accretion models are reviewed, and adaptations for automotive applications are discussed. Based on the new capabilities developed by the Weather on Wheels (WoW) program at Ontario Tech University, a model architecture is proposed in order to progress toward adequate snow accretion predictions for autonomous vehicle operating conditions, and preliminary results are presented. [ABSTRACT FROM AUTHOR]

Downbursts are cold descending winds that develop from thunderstorm clouds and, after impingement on the ground, produce an intense low-level horizontal front characterized by an axisymmetric toroidal vortex structure. Surface roughness is a key factor in the characterization of mean and turbulent wind speed features of synoptic-scale stationary atmospheric boundary layer winds. The goal of the present research is to physically assess whether the same can apply to the surface layer produced during thunderstorms, which are non-stationary, highly time-transient, and spatially limited phenomena. Downburst-like flows were produced through the impinging jet technique at the WindEEE Dome, at Western University in Canada. Three different surfaces were tested, and an equivalent full-scale roughness length ( z 0 , eq ) was determined. Experimental records are made publicly available. The large geometric and kinematic scales produced high Reynolds numbers, which enabled us to classify the flow as "fully turbulent" and therefore representative of full-scale downbursts. Results indicate a weak dependency on the Reynolds number, which suggests no relevant flaws in extending the results to the natural environment. The overall wind speed maxima weakly depend on z 0 , whereas a sharp velocity decrease is observed beyond the radial position of the maxima with increasing z 0 . Surface roughness enhances the boundary layer separation and consequently elevates the height of maximum wind speed above the surface. Vertical profiles of the horizontal velocity return a quite clear nose shape. Turbulence intensity shows a C-like shape with maxima in the near proximity of the ground that increase with z 0 . [ABSTRACT FROM AUTHOR]

Thunderstorm winds are cold descending gravity currents whose impingement on the ground creates strong radial outflows with maximum wind speeds in the near-ground region. They represent one of the greatest hazards for natural and built environment as well as one of the deadliest phenomena all over the world. This study carries on the post-processing analyses of the downburst experimental campaign performed at the WindEEE Dome, at Western University in Canada, in the context of the ERC project THUNDERR. While a former study presented the interaction between downburst and atmospheric boundary layer (ABL) winds, here the focus is on the influence exerted by the thunderstorm cloud translation. This was experimentally replicated at large scale by means of impinging jet technique where the jet axis was inclined to a non-zero angle with respect to the vertical. Finally, the inclusion of background ABL wind allowed to reconstruct the complete three-dimensional and non-stationary nature of the phenomenon. The outflow radial symmetry is lost in case of inclined jet axis. This leads to an intensification of the front-wind side and weakening of the rear-wind side, where the entrainment of the counter-directed ABL wind, and consequent flow speed-up, are not as pronounced as in the vertical-axis case. The non-linearity of the complex interaction between downburst, ABL flow and cloud translation is proven and quantified. Vertical profiles of mean wind speed and turbulence intensity are discussed in relation to the mutual interaction among flow components. [ABSTRACT FROM AUTHOR]

Abstract Thunderstorm winds and their interaction with structures are transient. The transient nature of downbursts is related to their embedment into stationary atmospheric boundary layer (ABL) winds. This paper introduces a signal analysis technique for the detection of abrupt changes in wind velocity time series with transient features. The detection method is then applied to explore the superposition between a straight wind and a downburst-like outflow. To study this interaction, the WindEEE Dome at Western University simultaneously produced straight and impinging jet flows in a closed-circuit mode of operation. The strength and characteristics of these two flows (when simultaneously produced) are studied herein for nine different flow rate ratios between the two types of flows. The method defined for detection of abrupt changes in velocity signals is used to determine the beginning of the impinging jets, as well as the slowdown of the ABL winds. In addition, the proposed methodology is tested for the case of a real downburst event recorded in Livorno, Italy, on 1 October 2012. The method accurately identifies abrupt changes in both mean and standard deviation of velocity signals in transient flows. The largest interference between ABL and downburst winds occurs when both flows are weak. Highlights • Impinging jets in straight flows investigated in a closed-circuit wind simulator. • Nine intensities of impinging jets and straight flows analyzed. • A method for detection of changepoints in transient velocity records introduced. • The changepoints method tested for experimental and full scale velocity records. • Largest interference between jet and straight flows when both flows are weak. [ABSTRACT FROM AUTHOR]

We present a flexible solution for the representation of forest edges in windtunnel experiments that can be easily adapted to match observed wind statistics from fullscale field experiments. The solution is based on an incremental approach in which layers of coarse mesh are wrapped over a matrix of cylinders. The mesh layers increase the drag of the model canopy, while they also realistically simulate the strong damping of turbulent fluctuations inside the canopy. In addition to adding layers of mesh, the original 90 degree angle of the forest edge is tapered such that it more closely resembles the profile of the forest edge from a field experiment. The high vertical resolution of the wind-tunnel observations for the calibrated forest model shows both more detail and confirms previous findings from the field experiment. For example, in the region just above the canopy, where the slower wind flow inside the canopy mixes with the faster flow aloft, the streamwise skewness shows a strong zigzag pattern as a function of height and an increase in the streamwise velocity standard deviation. [ABSTRACT FROM AUTHOR]

The effects of surface roughness on the target flow properties of tornadoes, like the maximum tangential velocity and core size, are not well understood and widely debated due to the discrepancies reported by previous studies. This study presents the results of large eddy simulations of "tornado-like" vortices (TLVs) of swirl ratios in the range of 0.22–1.00 over five ground roughness scenarios. The results indicate that roughness enhances flow convergence and reduces the core radius near the ground, except at the transition swirl ratio. Our study supports the widely reported claim that surface roughness has an effect similar to a reduction in swirl ratio. A reduction in core radius is accompanied by a speed-up in the tangential velocity due to the principle of conservation of angular momentum. The trends in maximum tangential velocity are, however, more height-sensitive due to the competing effects of depleting angular momentum in the surface layer and speed-up due to enhanced flow convergence. The results indicate that the effect of surface roughness on TLV characteristics is strongly dependent on the external swirl ratio. The lack of consensus in the literature is due to the limited range of swirl ratios and roughness considered in those studies. • LES of TLVs for different swirl ratios and ground roughness scenarios is carried out. • Roughness reduces the vortex size near the ground except at the transition swirl ratio. • Drowned vortex jump occurrence shifts to higher external swirl ratios. • The trends in maximum tangential velocity are less trivial to generalize due their sensitivity to height. [ABSTRACT FROM AUTHOR]

Several engineering and media reports have demonstrated that luminary and lighting poles are susceptible to tornadic wind actions. This paper provides the first dynamic structural analysis of a 1:50 geometrically scaled model of a generic luminary pole of a circular cross-section tested under transient wind loads caused by translating tornado-like vortices (TLVs). The physical experiments were performed in the WindEEE Dome tornado simulator at Western University (Canada). The tornadic wind actions on the pole are also compared against the reference atmospheric boundary layer (ABL) wind gust with the mean recurrent period of 50 years. Three different positions of the luminary pole in respect to the TLV path were considered: (1) TLV center passing over the pole; (2) TLV core radius passing over the pole; and (3) an intermediate case in which the pole was positioned between the TLV center and the core radius. In all cases two circular cylinders of different diameters were used to simulate two different cross-sections of an actual luminary pole. Our study demonstrates that luminary poles are more susceptible to tornadic wind actions compared to ABL winds. The tip displacements of the pole were larger in the TLVs and the direction and magnitude of the displacements were dependent on the relative positions of the TLVs and the luminary pole. The highest wind forces were observed in the regions characterized by strong tangential wind speeds. The entire luminary pole was subjected to negative pressure coefficients during the TLV passage. However, our structural analysis showed that the pole always stayed in the elastic region of deformation and there was no permanent bending or collapse of the structure. • Dynamic structural analysis of luminary pole subjected to tornado-like winds. • Tornadic wind actions compared against those of atmospheric boundary layer (ABL) winds. • Luminary poles are more susceptible to tornadic wind actions compared to ABL winds. • Three pole positions in respect to passing tornado-like vortices considered. [ABSTRACT FROM AUTHOR]