Boundary Layer Wind Tunnel Research Articles

Physical simulation of downburst winds for civil structures: A review

Complementary to field measurement and computational simulation, experimental generation of downburst winds in laboratories is an effective approach to enhance the understanding of the wind characteristics and the induced loads on civil structures. This study reviews the literature in physical simulation of downburst winds, while capturing historic background, highlighting recent advances, and illuminating future trends. A total of 23 testing facilities, classified into three categories of standalone simulators (12 facilities), modified boundary layer wind tunnels (five facilities), and multi-fan wind tunnels (six facilities), are discussed with their key features and representative studies. This paper serves as a valuable reference for future research in physical simulation of downburst winds.

Field measurements of wind load effects in a photovoltaic single-axis tracker mounting rail

The demand for solar photovoltaic power installations has resulted in a highly competitive industry. Equipment suppliers are under pressure to reduce design margins for projects to be feasible. Single-axis trackers are widely used to increase yield and reduce the levelised cost of energy compared to fixed-tilt installations. Load coefficients on tracker arrays are usually quantified using model-scale studies conducted in atmospheric boundary layer wind tunnels. These dynamically sensitive structures have been known to suffer wind damage despite the use of modern design methods. Ongoing research into the support structure design is deemed important to ensure long-term reliability. The current study presents full-scale field data acquired over 109 days on an experimental one-in-portrait single-axis tracker facility located in the Western Cape, South Africa. The purpose of these measurements was to quantify wind load effects in two instrumented PV module mounting rails. Frequency domain data showed modal participation of both the torsional and bending modes of the torque tube. The effect of the bending mode was more pronounced for the rail furthest from a pile. Load coefficients calculated using experimental data were generally lower than those presented in ASCE 7-22. Fluctuating stresses at critical locations led to negligible fatigue damage.

Wind-induced interference effect of complex building clusters on long-span roof structures

The presence of complex buildings introduces interference effects and complicates the wind field around the long-span roof structure. The complexity of the problem makes it challenging to predict wind load of long-span roof structures, resulting in a scarcity of design data available to engineers and designers. Thus, the influence of interference effect on mean and peak pressure coefficients of a long-span tri-centered cylindrical roof structure was investigated through wind tunnel tests conducted in an atmospheric boundary layer wind tunnel. The study focused on the interference effects caused by two cooling towers, chimney, and some low-rise buildings, considering all wind directions. The results show that the interference effects are the result of a combination of amplification effects from the adjacent cooling towers and chimney and shielding effects from the surrounding low-rise buildings. Due to the shielding effect of low-rise buildings, the wind suction on the roof is mitigated compared to that of a single building, while at the end of the roof, wind suction is amplified by cooling tower effects. The interference effect of the building clusters, however, amplifies the fluctuating wind pressure coefficient and the peak pressure coefficient on the roof. To accurately estimate the wind load of building components and envelopes, furthermore, this study investigates the influence mechanism of interference effect on non-Gaussian characteristics of wind pressure combining with fluctuating wind pressure spectrum, spatial correlation of fluctuating wind pressure, and probability distribution characteristics of standardized wind pressure coefficient. The spatial correlation of wind pressure in the roof interference area exhibits a strong association, and the probability density distribution characteristics of the standardized wind pressure coefficient significantly deviate from the Gaussian curve, with a peak factor exceeding 3.5. Thus, it can be concluded that the wind pressure within this region demonstrates significant non-Gaussian characteristics. Hence, the zone values of peak pressure coefficients are determined using the peak factor approach to inform the wind resistance design of the envelope structure.

First experimental results on lifetime-aware wind farm control

The study presents the methodology, implementation, and first results of the experimental test of a lifetime-aware wind farm control (WFC) approach. The novel strategy goes beyond the conventional WFC formulations and aims to maximise profit while ensuring fulfilment of a desired lifetime. Damage due to fatigue is formulated using a cost model and is also limited by a lifetime constraint. The control strategy is based on yaw-induced wake steering and utilises a tool chain of power and damage estimators. The experiment was conducted with three model turbines in a boundary layer wind tunnel, which allowed the simulation of a realistic dynamic variation of the wind direction. The novel strategy is compared to conventional greedy operation, as well as to the classical maximum power strategy. The results show that the novel control strategy can improve the economic performance of the farm.

Validation of induction/steering reserve-boosting active power control by a wind tunnel experiment with dynamic wind direction changes

This paper presents an experimental validation of an active power control methodology that combines induction control and wake steering to maximize the power reserve of the wind turbines in a farm. The experiments are carried out on a cluster of three scaled wind turbines in a boundary-layer wind tunnel, by dynamically varying the wind direction, and by considering a time-varying power tracking signal that mimics secondary frequency control of the grid. The methodology is compared with three active power control algorithms sourced from the literature. Results indicate that the instantaneous power reserves are indeed improved by an appropriate handling of wake effects, achieving a more accurate tracking of the power signal.

Velocity-pressure admittance for structural analysis of large cooling towers against strong winds

To facilitate dynamic structural analyses of large cooling towers subjected to strong winds in structural design and safety assessments, the auto-spectra of the local wind pressures on the tower shell are required. To avoid expensive and laborious physical model tests, Pirner provided empirical normalized pressure spectra for direct use, which imply that the concept of velocity-pressure admittance can be applied in the windward region on the tower shell. However, Pirner's empirical results are subjected to the fact that the dependence of pressure spectra on height or turbulence intensity of the oncoming flow is wrongfully neglected. To this end, velocity-pressure admittances are measured at various heights on a 1:200 scaled tower model in an atmospheric boundary layer wind tunnel, and unified formulae for velocity-pressure admittance on windward region of large cooling towers are fitted out for use considering the turbulence intensity effects. The unified formulae are further validated using data measured on a 167 m high full-scale cooling tower in China. The full-scale/empirical formulae comparison indicates that the unified formulae for velocity-pressure admittance proposed are applicable on the windward side [0 degrees, 70 degrees]; while a constant of 1 should be utilized as the normalized power spectral density in the circumferential region [70 degrees, 180 degrees] in structural analyses.

Wall shear stress measurement using a zero-displacement floating-element balance

The floating-element (FE) principle, introduced nearly a century ago, remains one of the most versatile direct wall shear stress measurement methods. Yet, its intrinsic sources of systematic error, associated with the flow-exposed gap, off-axis load sensitivity, and calibration, have thus far limited its widespread application. In combination with the lack of standard designs and testing procedures, measurement reliability still hinges heavily on individual judgement and expertise. This paper presents a framework to curb these limitations, whereby the design and operation of a FE balance are leveraged by an analytical model that attempts to capture the behaviour and predict the relative contribution of the systematic sources of error. The design is based on a parallel-shift linkage and a zero-displacement force-feedback system. The FE has a surface area of 200×200\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$200\ imes 200\\,$$\\end{document} mm, and measurement sensitivity is adjustable depending on the surface condition and the Reynolds number. It is thus suitable for application in a wide range of low-speed, boundary-layer wind tunnels, small or large scale. Measurements of the skin friction coefficient over a smooth wall show a remarkable agreement with oil-film interferometry, especially for Reθ>1.3×104\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm Re}_{\ heta } > 1.3 \ imes 10^4$$\\end{document}. The discrepancy relative to the empirical Coles–Fernholz relation (κ=0.39\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\kappa = 0.39$$\\end{document} and C=4.352\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$C = 4.352$$\\end{document}) is within 0.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.5\\,$$\\end{document}%, and the level of uncertainty is below 1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1\\,$$\\end{document}% for a confidence interval of 95\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$95\\,$$\\end{document}%.

Full-scale experimental simulation of the stack effect pressure acting on an elevator door system in a high-rise building

The pressure-bearing performance of an elevator system under the stack effect in a super high-rise building is usually difficult to simulate directly in a laboratory environment due to the difficulty in fully meeting the similarity requirements. In this paper, a new full-scale experimental device for simulating stack pressure was designed in a large boundary layer wind tunnel laboratory, which was based on using wind pressure to simulate the action of thermal pressure on an elevator door system. By employing this approach, the pressure-bearing performances of an elevator door system under different levels of wind pressure of the static and dynamic conditions were systematically investigated, and the malfunction of the elevator door system due to the strong stack effect was successfully simulated. The critical pressure threshold of the elevator door system, which was difficult to evaluate accurately in previous studies, was then measured and it was approximately equal to 150 Pa. Meanwhile, the pressure-bearing state of the elevator door system was numerically simulated and compared with the wind tunnel experiment results. The study shows that the simulation employing the dynamic mesh model can accurately reflect the force characteristics of an elevator lobby door during its physical process of opening and closing. Finally, based on the experimental simulation results, the pressure-bearing thresholds of the elevator door systems of several typical high-rise buildings were estimated, and the reasonability of the full-scale simulation was finally verified by comparisons with field measurement data.

Impact of upstream fetch on environmental wind engineering applications

With the rapid urbanization process, there is a growing concern regarding the wind environment in suburban and urban regions. The purpose of this study is to investigate the influence of the upstream fetch length on environmental wind engineering issues, such as the pedestrian level wind (PLW) and the wind comfort assessment around newly built buildings. The suburban region of Westmount in Montreal and the urban area of Kowloon in Hong Kong are selected for case studies. The investigation has been experimental and results were obtained from two atmospheric boundary layer wind tunnels. The results indicate that the upstream fetch length that influences the PLW estimation in suburban areas is as short as 200 m and in urban areas is as short as 450 m. For the wind comfort assessment of a newly building, an upstream fetch length of 100 m from the building site can be utilized depending on the criteria used.

Floating wind turbine motion signature in the far-wake spectral content – a wind tunnel experiment

Abstract. The growing interest in floating offshore wind turbines (FOWTs) is rooted in the potential source of increased offshore energy production. As the technology is still in a pre-industrial state, several questions remain to be addressed where little field data are available. This study uses physical modelling at a reduced scale to investigate the signature of the floating motions into the wake spectral content of a simplified FOWT model. A wind turbine model based on the actuator disc concept is placed in an atmospheric boundary layer wind tunnel and subjected to a range of surge, heave and pitch motions. The signatures of idealised sinusoidal motion and realistic broadband motion on the model’s wake at distances of 4.6 D (D being the disc diameter) and 8 D are measured through the use of a rake of single hot wires. The spectral analysis shows that harmonic motion leaves clear signatures in the far wake's energy spectra, mainly in the top tip region, while broadband motion does not leave easily detectable signatures.

Computational Fluid Dynamics-Aided Simulation of Twisted Wind Flows in Boundary Layer Wind Tunnel

The twisted wind flow (TWF), referring to the phenomenon of wind direction varying with height, is a common feature of atmospheric boundary layer (ABL) winds, noticeably affecting the wind-resistant structural design and the wind environment assessment. The TWF can be effectively simulated by a guide vane system in wind tunnel tests, but the proper design and configuration of the guide vanes pose a major challenge as practical experience in using such devices is still limited in the literature. To address this issue, this study aims to propose an approach to determining the optimal wind tunnel setup for TWF simulations using a numerical wind tunnel, which is a replica of its physical counterpart, using computational fluid dynamics (CFD) techniques. By analyzing the mechanisms behind guide vanes for generating TWF based on CFD results, it was found that the design must take into account three key parameters, namely, (1) the distance from the vane system to the side wall, (2) the distance from the vane system to the model test region, and (3) the separation between the vanes. Following the optimal setup obtained from the numerical wind tunnel, TWF profiles matching both the power-law and Ekman spiral models, which, respectively, reflect the ABL and wind twist characteristics, were successfully generated in the actual wind tunnel. The findings of this study provide useful information for wind tunnel tests as well as for wind-resistant structural designs and wind environment assessment.

Full-Scale/Model Test Comparisons to Validate the Traditional Atmospheric Boundary Layer Wind Tunnel Tests: Literature Review and Personal Perspectives

For this paper, full-scale/model test comparisons to validate the traditional atmospheric boundary layer (ABL) wind-tunnel simulation technique performed until now by the wind engineering community are systematically reviewed. The engineering background includes some benchmark low-rise buildings specifically established for use in wind engineering research (the Aylesbury experimental buildings, the Texas Tech University experimental building, the Silsoe buildings, etc.), several high-rise buildings in North America and East Asia, long-span bridges, large-span structures, and cooling towers. These structures are of different geometries, are located in different wind environments, and are equipped with various transducers and anemometers. By summarizing the different articles in the literature, it is evident that notable discrepancies between the full-scale measurement and the model test results were observed in most full-scale/model test comparisons, which usually took certain forms: the mean and/or the peak negative pressures at the flow separation regions on buildings were underestimated in the wind tunnel; differences in the root-mean-square (rms) values of the acceleration samples between the full-scale measurements and the force balance model tests were non-negligible; the vertical vortex-induced vibration amplitudes of bridges measured using section models and aero-elastic models were much lower than those observed on the prototypes, etc. Most scholars subjectively inferred that inherent technical issues with the ABL wind tunnel simulation technique could be responsible for the observed full-scale/model test discrepancies, including the Reynolds number effects, the turbulent flow characteristics effects, and the non-stationarity effects. However, based on the authors’ years of experience and after discussion with experienced researchers, it was found that some of the full-scale measurements performed in earlier research were inherently less accurate and deterministic than the wind tunnel experiments they were supposed to validate, which could also be a significant cause of the full-scale/model test discrepancies observed. It is suggested herein that future studies in this field should regard full-scale measurements only as benchmarks, and that future works should focus on synthesizing the results from different schools of physical experiments and formulating universal empirical models of high theoretical significance to properly validate future wind tunnel tests.

Extreme Value Analysis for Peak Heliostat Wind Load Predictions

This study investigated high-frequency load fluctuations on a rectangular heliostat model in a boundary layer wind tunnel experiment. Statistical methods for peak wind load predictions were compared with load distributions through load cell and surface pressure measurements on the heliostat model placed in two simulated atmospheric boundary layers (ABLs) representing a flat desert terrain and open country terrain. It was found that statistical peak predictions based on horizontal wind gust velocity amplitude underestimates the load coefficients in stow and at oblique azimuth angles for maximum azimuth moments. In addition, it was shown that the distributions of the centre of pressure position and the hinge moment in stow position are non-Gaussian. It is therefore recommended that the frequency and amplitude of the vertical wind velocity component must be considered for peak load predictions of hinge moments and azimuth moments.

Flow Characteristics of the Boundary Layer Wind Tunnel at Tokyo Polytechnic University

Flow Characteristics of the Boundary Layer Wind Tunnel at Tokyo Polytechnic University

Introduction of Environmental Low-noise Boundary Layer Wind Tunnel at Institute of Industrial Science, The University of Tokyo

Introduction of Environmental Low-noise Boundary Layer Wind Tunnel at Institute of Industrial Science, The University of Tokyo

Introduction of Boundary Layer Wind Tunnel at Wind and Fluid Engineering Research Center, Niigata Institute of Technology

Introduction of Boundary Layer Wind Tunnel at Wind and Fluid Engineering Research Center, Niigata Institute of Technology

Prospect of LES for predicting wind loads and responses of tall buildings: A validation study

Wind load evaluation on buildings using large-eddy simulation (LES) poses several critical challenges. The most notable ones include accurately reproducing the approaching atmospheric boundary layer flow conditions and modeling massively separated flows around buildings. This study investigates the capability of LES for predicting cladding and overall loads on a tall building by addressing these key challenges. The results from LES are systematically validated against boundary layer wind tunnel measurements. The validation process unfolds in three key stages. Firstly, the approaching wind profiles were reproduced in LES by integrating a recently developed synthetic inflow turbulence generator with an implicit ground roughness modeling technique. Then, the statistics of the cladding and global loads were compared with the experiment for representative wind directions. Finally, the performance of the LES for predicting wind-induced response is examined, assuming typical structural properties for the building. Overall, the results obtained from each validation step showed encouraging agreement with the experimental measurement. In light of the findings from the current study, it is evident that LES is progressively realizing its potential to be a practical wind load evaluation tool. Selected simulation cases used in this study are available at .

A New Research Scheme for Full-Scale/Model Test Comparison of Wind Effects on Pengcheng Cooling Tower Based on Sinusoidal Flow Field Simulations

When examining the history of wind engineering, it is evident that many full-scale/model test comparisons have found noticeable differences between the results. Although understanding the causes of these differences is important for practical purposes, limited numerical and experimental conditions have often resulted in subjective explanations for full-scale/model test comparisons without scientific validation. To address this issue, this article suggests the use of the computational fluid dynamics technique or the multiple-fan actively controlled wind tunnel technique to quantitatively reveal the adverse effects that impact the reliability of the traditional atmospheric boundary layer wind tunnel tests for a large cooling tower, including not only the widely acknowledged influences (Reynolds number effects and turbulent flow characteristics effects) but also the non-stationarity effects that have potential influences. Established on the novel proposition, a new research scheme for future full-scale/model test wind effects comparisons for large cooling towers has been formulated based on the numerical or physical simulations of the sinusoidal flow fields. Using the Pengcheng cooling tower as a case study, the research recognized the very significant impact of Reynolds number effects, the non-stationarity effects that cannot be ignored, and the negligible effects of turbulent flow characteristics.

Finite dimensional models for wind diffusion process

Diffusion processes with linear drift and translations of Gaussian/non-Gaussian diffusion processes are fitted to wind pressure time series recorded at the University of Florida boundary layer wind tunnel facility (UFBLWT). The processes match exactly and approximately the marginal distributions and the correlation functions of these records. It is shown that these simple processes and their finite dimensional models characterize accurately the extremes of the wind record under consideration provided their correlation functions minimize objective functions which account for extremes.

Effect of void space arrangement on wind power potential and pressure coefficient distributions for high-rise void buildings

High-rise void building complexes can augment the permeation of airflows over buildings, and thereby strengthen urban wind energy harvesting for realization of the sustainable development goals (SDGs). This paper considers the wind over a typical 2×2 compact high-rise building array with the openings to analyze the wind power potential at varying void sizes, locations of voids, and direction of incoming wind. The predicted mean wind speeds and turbulence intensities are compared against the measured data with 4 generic high-rise building models having voids in an atmospheric boundary layer wind tunnel for validation of the computational model. Based on the comparative results from four common Reynolds-averaged Navier-Stokes (RANS) turbulence models including the standard, realizable, renormalization group (RNG) k-ε, and shear-stress transport (SST) k-ω models as well as the Reynolds stress model (RSM), the RSM approach can provide the most accurate predictions of streamwise mean velocity and turbulence intensity. The present study then conducts CFD simulations to explore the effects of opening configuration and wind direction on the wind field around high-rise void buildings. Considering the variations of void sizes of 10 × 10 m2, 12.5 × 12.5 m2, 15 × 15 m2, void heights of z/H = 0.25, 0.5, 0.75 and wind directions of 0°, 45°, respectively, the simulated results indicate elevated wind power densities with acceptable turbulence intensities over the upstream gap passage and void channels to achieve prospective urban wind power harvest and mitigate wind load on structures of high-rise void buildings.