Crosswind Direction Research Articles

Importance of parameter optimization in a nonlinear stabilized method adding a crosswind diffusion

Numerical solutions of convection-dominated problems are known to exhibit spurious oscillations whose suppression requires the use of numerical stabilization. Stabilized methods which involve heuristic parameters are often applied. The parameters influence the quality of the solution but their optimal values are unknown.In this paper, we consider a stabilization method which adds numerical diffusion adaptively, based on minimizing a functional. The novelty of our approach consists in combining an error indicator with reduced residuals with a nonlinear SOLD method adding artificial diffusion in the crosswind direction. We demonstrate that this approach can lead to more physically meaningful solutions than techniques considered before.

Bilateral Interference of Wind Loads Induced on Duplicate Building Models of Various Shapes

The current investigation focuses on the results of an experimental investigation of Square-plan-shape and Remodel-triangle-shape building model’s varied interference conditions between duplicate building models of 1:300 scale (at 100% blockage) on wind-induced pressure and base moments at fixed 10% of the height of the instrumented model. Under current working conditions, the study concludes that -1 > Interference Factor > 1 as experienced by the Remodel-triangle-shape model results in reduced performance of the instrumented model as opposed to the Square-plan-shape model. Front-to-Front interference condition of Remodel-triangle-shape model has the best overall performance in along-wind and crosswind directions, whereas Front-to-Back interference condition of Remodel-triangle-shape model has the best torsional performance. Back-to-Back interference of a Remodel-triangle-shape model should be avoided because the orientation of duplicate models attracts the most overturning moments in both the along-wind and crosswind directions of all interference conditions investigated in this study.

Optimization of alongwind and crosswind force coefficients on a tall building with horizontal limbs using surrogate modeling

SummaryFor tall buildings, values of wind force coefficients can be obtained from wind tunnel tests or Computational Fluid Dynamics (CFD). This paper is concentrated to analyze a set of CFD data and propose parametric equations for determining force coefficients in the alongwind and crosswind direction (Cfx and Cfy) of tall buildings with horizontal limbs. Initially, a parametric study is performed with CFD analysis considering RANS k − ε turbulence models keeping a constant plan area 22,500 mm2. The length and velocity scales are taken as 1:300 and 1:5, respectively. The required design parameters are obtained and used for fitting parametric equations. The CFD data are further utilized for training artificial neural networks of Cfx and Cfy. The results of CFD, ANN, and parametric equations are compared. The parametric equations are validated by employing a wind tunnel study. Finally, three optimization studies are carried out using a genetic algorithm (GA), of which the first two aim to present the maximum and minimum force coefficients considering single objectives. The third optimization is a multi‐objective optimization problem, carried out to simultaneously minimize and maximize the two orthogonal force coefficients. Pareto‐optimal design results are presented.

Component Combination Rules of Wind Load Effects of Building Structures

Under the action of the same wind azimuth, the extreme values of the wind load effect components of building structures are generated in the along-wind, cross-wind, vertical, and torsional directions. In designing the wind-resistant structure, the extreme values of effect components need to be combined to determine the internal force envelope values of members. Complete quadratic combination (CQC) and Turkstra combination rules are often used to determine the combination value of extreme values of wind effect components. The extreme probability distribution expressions of the CQC, and the Turkstra and approximate rules, are derived. The simplified combination Equations and combination coefficients of the CQC and Turkstra approximate rules are proposed in this paper. We use the combination Equations and Monte Carlo simulation method to analyze the accuracy of Turkstra and its approximate rules. The results show that the combination extreme is associated with the correlation coefficients, mean values, ratios of standard deviations, and fluctuating extremes of effect components. The errors between Turkstra and its approximate rules are small when load effect components show a positive correlation. The errors are largest when the standard deviations of components are equal. Our research results provide a theoretical basis for the combination method of wind load effect components of building structures.

Effectiveness of a tiny tuned liquid damper on mitigating wind-induced responses of cylindrical solar tower based on elastic wind tunnel tests

A tiny TLD was specially designed and manufactured to investigate its effectiveness on mitigating the wind-induced responses of a 243-meter-high solar tower by using wind tunnel tests based on an elastic test model. First, an elastic test model of the solar tower was made, and its structural parameters, including natural frequency, the first three mode shapes and structural damping ratio, were identified. Second, six types of tiny TLDs with different inner diameters (9, 10, 11, 12, 13 and 14 ​mm) were designed and manufactured, and the natural frequency and sloshing damping ratio of water in these tiny TLDs were identified to compare them with the theoretical values. The results show the measured and theoretical natural frequencies agree well with each other, while the measured sloshing damping of water is much larger than the theoretical value. Then, a series of wind tunnel tests were carried out to obtain the wind-induced responses of the solar tower. The effectiveness of TLD on mitigating the wind-induced responses of the solar tower was systematically investigated based on a series of parametric studies. The results show the wind-induced responses in the cross-wind and along-wind directions, including the acceleration at the top, the shear and moment at the bottom, can all be significantly reduced by the tiny TLDs with optimized parameters. It seems that the efficiency of the TLDs at the vortex-induced vibration critical wind velocity is significantly higher than that at the design wind velocity. In addition, the parametric studies indicate that the effectiveness of the TLDs is considerably sensitive to the frequency ratio, the height of the TLDs and the mass ratio.

Aerodynamic Characteristics of Helicopter with Ducted Fan Tail Rotor in Hover under Low-Speed Crosswind

The tail rotor of a helicopter operating under low-speed crosswind undergoes highly complex flow due to the interaction between the main rotor, fuselage, and tail rotor system. In this study, numerical simulations have been conducted on the complete configuration of a helicopter with a ducted fan tail rotor system (comprising a main rotor, ducted fan tail rotor, fuselage, and empennage) to analyze the wake interaction in hovering flight under various crosswind directions. The flow characteristics around the tail rotor, the tail rotor thrust, and the yawing moment of the helicopter are investigated and evaluated. The aerodynamic forces are compared with those of a helicopter with an open-type tail rotor. The results indicate that the aerodynamic performance of the ducted fan tail rotor is highly affected by the wakes of both the main rotor and port wing. Nevertheless, the helicopter with a ducted fan tail rotor is observed to be much more directionally stable under various crosswind directions, than that with an open-type tail rotor. This is because the rotor is protected by the fixed part of the tail rotor system in the former case.

Wind Tunnel Investigations of Aeroelastic Electricity Transmission Tower under Synoptic and Typhoon Winds

Wind tunnel tests of an aeroelastic tower model at a length scale of 1∶40 were conducted to investigate the dynamic responses of an electricity transmission tower under synoptic and typhoon winds. The aeroelastic tower model was successively subjected to boundary layer and typhoon wind forcing in a single wind tunnel. The purpose of this study is to assess differences of the dynamic structural responses under two types of wind forcing and understand the underlying mechanism of transmission tower failures due to strong typhoons. The results indicated that the acceleration responses of the aeroelastic tower model were composed of resonant and background parts, while dominated by the resonant counterpart, and the dynamic responses of the transmission tower could be increased by up to 30% in the along-wind and crosswind directions under typhoon wind forcing. The wind load factors determined from the experimental results under typhoon winds were generally larger than those obtained from Chinese codes and standards. Suggestions on the wind-resistant design of an overhead transmission tower in typhoon-prone areas were proposed. The dynamic wind loads should be substituted by the most conservative values among different Chinese standards in estimating the equivalent static wind loadings of overhead towers under typhoon wind forcing.

Retrieval of Sea Surface Wind Speed from Spaceborne SAR over the Arctic Marginal Ice Zone with a Neural Network

In this paper, we presented a method for retrieving sea surface wind speed (SSWS) from Sentinel-1 synthetic aperture radar (SAR) horizontal-horizontal (HH) polarization data in extra-wide (EW) swath mode, which have been extensively acquired over the Arctic for polar monitoring. In contrast to the conventional algorithm, i.e., using a geophysical model function (GMF) to retrieve SSWS by spaceborne SAR, we introduced an alternative retrieval method based on a GMF-guided neural network. The SAR normalized radar cross section, incidence angle, and wind direction are used as the inputs of a back propagation (BP) neural network, and the output is the SSWS. The network is developed based on 11,431 HH-polarized EW images acquired in the marginal ice zone (MIZ) of the Arctic from 2015 to 2018 and their collocated scatterometer wind measurements. Verification of the neural network based on the testing dataset yields a bias of 0.23 m/s and a root mean square error (RMSE) of 1.25 m/s compared to the scatterometer wind data for wind speeds less than approximately 30 m/s. Further comparison of the SAR retrieved SSWS with independent buoy measurements shows a bias and RMSE of 0.12 m/s and 1.42 m/s, respectively. We also analyzed the uncertainty of the retrieval when reanalysis model wind direction data are used as inputs to the neural network. By combining the detected sea ice cover information based on SAR data, sea ice and marine-meteorological parameters can be derived simultaneously by spaceborne SAR at a high spatial resolution in the Arctic.

Mutual Interaction between Surface Waves and Langmuir Circulations Observed in Wave-Resolving Numerical Simulations

AbstractWave-resolving simulations of monochromatic surface waves and Langmuir circulations (LCs) under an idealized condition are performed to investigate the dynamics of wave–current mutual interaction. When the Froude number (the ratio of the friction velocity of wind stress imposed at the surface and wave phase speed) is large, waves become refracted by the downwind jet associated with LCs and become amplitude modulated in the crosswind direction. In such cases, the simulations using the Craik–Leibovich (CL) equation with a prescribed horizontally uniform Stokes drift profile are found to underestimate the intensity of LCs. Vorticity budget analysis reveals that horizontal shear of Stokes drift induced by the wave modulation tilts the wind-driven vorticity to the downwind direction, intensifying the LCs that caused the waves to be modulated. Such an effect is not reproduced in the CL equation unless the Stokes drift of the waves modulated by LCs is prescribed. This intensification mechanism is similar to the CL1 mechanism in that the horizontal shear of the Stokes drift plays a key role, but it is more likely to occur because the shear in this interaction is automatically generated by the LCs whereas the shear in the CL1 mechanism is retained only when a particular phase relation between two crossing waves is kept locked for many periods.

Wind tunnel testing of the effect of terrain on the wind characteristics of airport glide paths

To study the effect of complex terrain on the wind characteristics of the glide paths at Hong Kong International Airport’s North Runway, wind tunnel testing was conducted in Tongji University’s TJ-3 boundary layer wind tunnel, and Cobra probes were used to measure the wind speed and wind direction at the North Runway glide paths. The effects of terrain on the wind characteristics, including turbulence intensity, turbulence integral scale, and mean headwind speed were analysed. The results show that the terrain fluctuations have a significant effect on the wind characteristics of the glide paths. The turbulence intensities in the cross-wind direction and the vertical direction increase with increasing turbulence intensity in the wind direction at the same altitude; the inflow may affect aircraft landing due to the decrease in headwind speed at glide path 25RA caused by the obstruction of certain terrain.

Experimental study on wind speeds in a complex-terrain wind farm and analysis of wake effects

In this paper, wind speed deficits have been quantified based on the field observations from the hilly Shiren wind farm in China. Two lidars have been applied to measure wind speeds in the wind farm. Two clusters of wind turbines in different layout patterns were chosen for the experiments. One cluster was the upstream-and-downstream pattern, which was used to investigate the upstream turbine’s wake impact on the downstream turbine. According to the experiment, the wake width of the downstream turbine widened and the largest wind speed deficit decreased gradually in the downstream direction. Meanwhile, the wake centerlines of upstream and downstream wind turbines were subjected to the wind direction and may not be in the same line. The other cluster was the side-by-side pattern, which was to investigate how the wakes and the wake interactions develop downwind of a row of wind turbines. It has been found that huge wind speed deficits existed behind the wind turbines. The wind speeds reduced mostly from 14.4 m/s to 8.0 m/s in the downwind direction and from 12.4 m/s to 4.2 m/s in the crosswind direction. Wind speeds were not stable in the far-wake zone. The wake boundary was not easy to determine as well. When wakes of two adjacent turbines encountering, the interaction effect became complicated. In these experiments, the complex terrain is one of the most important factors that complicates the wake distribution. Therefore, the influence of the terrain shape on wake distribution should be continuously investigated in the future.

Experimental Study of Wind Pressure on a Long-Span Canopy Roof Structure Using a Wind Tunnel

The wind pressure characteristics of the surface of a long-span canopy roof structure were investigated in detail using synchronized pressure measurement tests on a rigid model in an atmospheric boundary layer wind tunnel. The mean and fluctuating wind pressure distribution characteristics, power spectral density and coherence of the fluctuating wind pressure between different measurement points were analyzed. The results showed that the wind direction had a significant impact on the wind load distribution across the surface of the long-span canopy roof structure. When the short axis of the roof structure faced the wind, a positive pressure area was formed under the impact of the incoming flow, with the resulting turbulence being the main cause of excitation. When the long axis of the roof structure faced the wind (wind directions of 0° and 180°), a columnar vortex was formed on the windward side of the front edge of the roof structure and a suction force was created at the separation points, with the main excitation of the wind load being intermittent vortex shedding. The resulting spectral content was complex. The coherence of the measurement points on the roof structure surface decreased continuously as the distance between them increased. The correlation between the same two measurement points obviously also differed according to the wind direction. However, the coherence between measurement points aligned to the wind direction was stronger than it was in a cross-wind direction.

Field measurement on the three-dimensional thermal characteristics of a single air inlet induced draft cooling tower

This study introduces the field measurement on a single air inlet induced draft cooling tower (SIDCT) under crosswind conditions. A three-dimensional numerical model is developed and validated to collaborate with the field measurement. The primary objective of this study is to evaluate the effect of environmental crosswind (both direction and velocity) on the thermal characteristics of SIDCT, such as air/water ratio, range, approach, Merkel number, heat transfer coefficient, etc. Measurement results demonstrate that as crosswind velocity rises, the ventilation and cooling performance of SIDCT are continuously enhanced under the crosswind directions of α1 and α2, while significantly decreased under α3. As air flows into SIDCT along the depth direction, the air temperature above drift eliminatorsdecreases firstlyandthen increases, which follows a reverse trend to the distribution pattern of air velocity. With the increasing crosswind velocity, the water temperature drop increases in the rain zone under α1 and decreases in the fill zone under α3, while the cooling capacity decreases in the fill zone and increases in the rain zone, regardless of the crosswind direction. The fitted correlations are derived for predicting the performance parameters with respect to crosswind velocity and direction.

Using computational fluid dynamics and field experiments to improve vehicle-based wind measurements for environmental monitoring

Abstract. Vehicle-based measurements of wind speed and direction are presently used for a range of applications, including gas plume detection. Many applications use mobile wind measurements without knowledge of the limitations and accuracy of the mobile measurement system. Our research objective for this field-simulation study was to understand how anemometer placement and the vehicle's external airflow field affect measurement accuracy of vehicle-mounted anemometers. Computational fluid dynamic (CFD) simulations were generated in ANSYS Fluent to model the external flow field of a research truck under varying vehicle speed and wind yaw angle. The CFD simulations provided a quantitative description of fluid flow surrounding the vehicle and demonstrated that the change in wind speed magnitude from the inlet increased as the wind yaw angle between the inlet and the vehicle's longitudinal axis increased. The CFD results were used to develop empirical speed correction factors at specified yaw angles and to derive an aerodynamics-based correction function calibrated for wind yaw angle and anemometer placement. For comparison with CFD, we designed field tests on a square, 12.8 km route in flat, treeless terrain with stationary sonic anemometers positioned at each corner. The route was driven in replicate under varying wind conditions and vehicle speeds. The vehicle-based anemometer measurements were corrected to remove the vehicle speed and course vector. From the field trials, we observed that vehicle-based wind speed measurements differed in average magnitude in each of the upwind, downwind, and crosswind directions. The difference from stationary anemometers increased as the yaw angle between the wind direction and the truck's longitudinal axis increased, confirming the vehicle's impact on the surrounding flow field and validating the trends in CFD. To further explore the accuracy of CFD, we applied the function derived from the simulations to the field data and again compared these with stationary measurements. From this study, we were able to make recommendations for anemometer placement, demonstrate the importance of applying aerodynamics-based correction factors to vehicle-based wind measurements, and identify ways to improve the empirical aerodynamic-based correction factors.

Small-Scale Dispersion in the Presence of Langmuir Circulation

AbstractWe present an analysis of ocean surface dispersion characteristics, on 1–100-m scales, obtained by optically tracking a release of bamboo plates for 2 h in the northern Gulf of Mexico. Under sustained 5–6 m s−1 winds, energetic Langmuir cells are clearly delineated in the spatially dense plate observations. Within 10 min of release, the plates collect in windrows with 15-m spacing aligned with the wind. Windrow spacing grows, through windrow merger, to 40 m after 20 min and then expands at a slower rate to 50 m. The presence of Langmuir cells produces strong horizontal anisotropy and scale dependence in all surface dispersion statistics computed from the plate observations. Relative dispersion in the crosswind direction initially dominates but eventually saturates, while downwind dispersion exhibits continual growth consistent with contributions from both turbulent fluctuations and organized mean shear. Longitudinal velocity differences in the crosswind direction indicate mean convergence at scales below the Langmuir cell diameter and mean divergence at larger scales. Although the second-order structure function measured by contemporaneous GPS-tracked surface drifters drogued at ~0.5 m shows persistent r2/3 power law scaling down to 100–200-m separation scales, the second-order structure function for the very near surface plates observations has considerably higher energy and significantly shallower slope at scales below 100 m. This is consistent with contemporaneous data from undrogued surface drifters and previously published model results indicating shallowing spectra in the presence of direct wind-wave forcing mechanisms.

Reformative translation model for probability density functions of amplitude processes of crosswind-excited super-tall buildings

At the vicinity of vortex lock-in wind speed, the nonlinear aerodynamic damping effect of super-tall buildings is significant, which can greatly promote the surge of vortex-induced vibration in the crosswind direction, where the crosswind response characterized by harmonic amplitude shows narrow-band hardening non-Gaussian characteristic with the kurtosis well below 3, and the corresponding probability distribution of amplitude process distinctly differs from that of typical random buffeting response. Although the moment-based Hermite translation model has been widely used for estimating the extreme value distribution of non-Gaussian process, it fails to represent the probability distribution of hardening non-Gaussian amplitude process, notably for the response with a kurtosis close to 1.5. In this study, a new translation model based on orthogonal expansion of random processes is developed for obtaining the non-Gaussian amplitude process from an underlying Gaussian amplitude process, and the probability density function of the non-Gaussian amplitude process is derived by mapping the cumulative distribution function. The coefficients of translation model are determined by minimizing the errors between the estimated probability density functions and target values through nonlinear optimization, and the closed-form semi-empirical formulations, which connect the model coefficients with response kurtosis, are also proposed using least-square curve fitting. Moreover, the effectiveness and monotonicity of the proposed translation model are examined. This model can be readily incorporated into the extreme value analysis of crosswind response and facilitate the evaluation of wind-induced fatigue of super-tall buildings.

Coincident Observations of Dye and Drifter Relative Dispersion over the Inner Shelf

AbstractCoincident Lagrangian observations of coastal circulation with surface drifters and dye tracer were collected to better understand small-scale physical processes controlling transport and dispersion over the inner shelf in the Gulf of Mexico. Patches of rhodamine dye and clusters of surface drifters at scales of O(100) m were deployed in a cross-shelf array within 12 km from the coast and tracked for up to 5 h with airborne and in situ observations. The airborne remote sensing system includes a hyperspectral sensor to track the evolution of dye patches and a lidar to measure directional wavenumber spectra of surface waves. Supporting in situ measurements include a CTD with a fluorometer to inform on the stratification and vertical extent of the dye and a real-time towed fluorometer for calibration of the dye concentration from hyperspectral imagery. Experiments were conducted over a wide range of conditions with surface wind speed between 3 and 10 m s−1 and varying sea states. Cross-shelf density gradients due to freshwater runoff resulted in active submesoscale flows. The airborne data allow characterization of the dominant physical processes controlling the dispersion of passive tracers such as freshwater fronts and Langmuir circulation. Langmuir circulation was identified in dye concentration maps on most sampling days except when the near surface stratification was strong. The observed relative dispersion is anisotropic with eddy diffusivities O(1) m2 s−1. Near-surface horizontal dispersion is largest along fronts and in conditions dominated by Langmuir circulation is larger in the crosswind direction. Surface convergence at fronts resulted in strong vertical velocities of up to −66 m day−1.

Development of a parameterized reduced-order vertical-axis wind turbine wake model

Analyzing or optimizing wind farm layouts often requires reduced-order wake models to estimate turbine wake interactions and wind velocity. We propose a wake model for vertical-axis wind turbines in streamwise and crosswind directions. Using vorticity data from computational fluid dynamic simulations and cross-validated Gaussian distribution fitting, we produced a wake model that can estimate normalized wake velocity deficits of an isolated vertical-axis wind turbine using normalized downstream and lateral positions, tip-speed ratio, and solidity. Compared with computational fluid dynamics, taking over a day to run one simulation, our wake model predicts a velocity deficit in under a second with an appropriate accuracy and computational cost necessary for wind farm optimization. The model agreed with two experimental studies producing percent differences of the maximum wake deficit of 6.3% and 14.6%. The wake model includes multiple wake interactions and blade aerodynamics to calculate power, allowing its use in wind farm layout analysis and optimization.

Field Research on the Wind-Induced Response of a Super High-Rise Building under Typhoon

This paper simultaneously measures the characteristics of wind on the roof and the acceleration responses of the 10th, 18th, 25th, 32nd and 41st floors of a high-rise building in Wenzhou during the passing of typhoons between 2014 and 2016. This paper also analyses the dynamic characteristics and wind-induced response of buildings by using Welch and improved Natural Excitation Technique–Eigensystem Realisation Algorithm methods. The results show that the typhoons that affected Wenzhou are dominated by wind from the east, northeast and northwest. The acceleration response probability densities of different floors during Typhoons Chan-hom and Dujuan are similar to the Gaussian distribution. The first-order natural frequencies of the two wind directions of the test building are 0.390 and 0.409, which are in good agreement with Tamura’s prediction results. The relevant amplitude and frequency characteristics of the first three modes are investigated in detail according to the nonlinear characteristics of the measured building. The first-, second- and third-order damping ratios of the structure during Typhoons Chan-hom and Dujuan increased with the peak acceleration, whereas the damping during Typhoon Fung-wong remained almost unchanged. The root mean square of the acceleration response of the building structure during Typhoons Chan-hom and Dujuan increased with the wind speed. However, the increase rate of Typhoon Chan-hom was small, possibly because the angle between the incoming flow and the building is 45°, and the acceleration response in the downwind and crosswind directions is not apparent. The measured results show that the working environment of the staff at the top of the building under the influence of the typhoon also meets comfort requirements. The measured data and statistical parameters provide a valuable reference for the wind-resistant design of high-rise buildings in typhoon-prone areas.

Comparison of inflow-turbulence and trailing-edge noise models with measurements of a 200-kW vertical axis wind turbine

Models of inflow-turbulence noise and turbulent-boundary-layer trailing-edge noise are compared to earlier measurements of a 200-kW vertical axis wind turbine so that conclusions regarding the origin of the aerodynamic noise can be drawn. The measurement campaigns, which aimed at establishing the noise emission value and locating the aerodynamic noise sources with a microphone array, are here both compared to further modified versions of the trailing-edge and inflow-turbulence models respectively. Unlike the case for horizontal axis wind turbine, inflow-turbulence noise is deemed as the prevailing noise mechanism. Reducing the self-induced turbulence could then be an effective way of lowering the noise levels for vertical axis wind turbines. Also, looking at the directivity of the inflow-turbulence noise model which indicate most noise in the cross-wind directions, a deviation from the standard downwind measurement position for measuring noise emission is suggested for the VAWT case.