Physical Wind Tunnel Research Articles

Numerical-physical modelling of the long jump flight of female athletes: Impact of jump style, hairstyle and clothing

The long jump is a track and field event in which the athlete sprints down a runway and tries to leap as far as possible from a take-off line. To the best of our knowledge, there are no published studies on the aerodynamic impact of jump style, hairstyle and clothing on the long jump distance. This paper presents a numerical-physical model of the long jump flight. It allows to predict flight distance and the impact of jump style, hairstyle and clothing. It consists of five submodels: an existing model of the sprint before take-off, a computational fluid dynamics (CFD) model of different body postures in flight, a set of physical wind tunnel models for CFD validation, a full-scale wind tunnel manikin with different hairstyles and clothing and a numerical model of the flight trajectory. Jump style only impacts flight distance by 1 cm or less. Hairstyle and clothing however can cause drag to vary by more than 25% and flight distance by more than 10 cm, mostly by impacting the take-off speed. In the long term, long jump events might see the introduction of hair caps and low-drag clothing to reduce aerodynamic resistance and level the playing field.

Developing a digital twin framework for wind tunnel testing: validation of turbulent inflow and airfoil load applications

Abstract. Wind energy systems, such as horizontal-axis wind turbines and vertical-axis wind turbines, operate within the turbulent atmospheric boundary layer, where turbulence significantly impacts their efficiency. Therefore, it is crucial to investigate the impact of turbulent inflow on the aerodynamic performance at the rotor blade scale. As field investigations are challenging, in this work, we present a framework where we combine wind tunnel measurements in turbulent flow with a digital twin of the experimental set-up. For this, first, the decay of the turbulent inflow needs to be described and simulated correctly. Here, we use Reynolds-averaged Navier–Stokes (RANS) simulations with k−ω turbulence models, where a suitable turbulence length scale is required as an inlet boundary condition. While the integral length scale is often chosen without a theoretical basis, this study derives that the Taylor micro-scale is the correct choice for simulating turbulence generated by a regular grid: the temporal decay of turbulent kinetic energy (TKE) is shown to depend on the initial value of the Taylor micro-scale by solving the differential equations given by Speziale and Bernard (1992). Further, the spatial decay of TKE and its dependence on the Taylor micro-scale at the inlet boundary are derived. With this theoretical understanding, RANS simulations with k−ω turbulence models are conducted using the Taylor micro-scale and the TKE obtained from grid experiments as the inlet boundary condition. Second, the results are validated with excellent agreement with the TKE evolution downstream of a grid obtained through hot-wire measurements in the wind tunnel. Third, the study further introduces an airfoil in both the experimental and the numerical setting where 3D simulations are performed. A very good match between force coefficients obtained from experiments and the digital twin is found. In conclusion, this study demonstrates that the Taylor micro-scale is the appropriate turbulence length scale to be used as the boundary condition and initial condition to simulate the evolution of TKE for regular-grid-generated turbulent flows. Additionally, the digital twin of the wind tunnel can accurately replicate the force coefficients obtained in the physical wind tunnel.

Extrapolating wind pressures on roof soffits of low-rise buildings using few-shot learning

Current wind standards assume identical external wind pressure coefficients on roof soffits and adjacent wall surfaces. However, recent experiments suggest that this correlation significantly decreases with an increase in overhang width. This research introduces a few-shot learning model addressing the need for a machine learning approach that can efficiently obtain the wind pressure coefficients on roof soffits when the overhang width is large (i.e., larger than 2 ft). This research proposed a few-shot learning model to extrapolate the wind-induced pressures on roof soffits for low-rise buildings based on the wind tunnel dataset investigating the three large overhang widths (i.e., 2.4, 4.8, and 7.2 inches in 1:10 scale models). Prior knowledge relating to zonal information and wind directions shown in the standard of minimum design loads and associated criteria for buildings and other structures (i.e., ASCE 7) is incorporated into the model. The proposed few-shot learning model was trained on scale model buildings with overhang widths of 2.4 and 4.8 inches and tested on a 7.2-inch overhang width case. When predicting the minimum wind pressure coefficient for both the southside and eastside soffit surfaces, low mean-squared errors and high coefficient of determination values were observed. This study marks the first application of few-shot learning techniques to extrapolate wind pressures across different roof overhang widths and provide reliable predictions that outperform the weak correlation between the soffit and the adjacent wall surface assumed currently. This model reduces reliance on physical wind tunnel experiments and requires only a low-resolution measurement tap configuration.

Physics-informed few-shot learning for wind pressure prediction of low-rise buildings

This research proposes a physics-informed few-shot learning model to predict the wind pressures on full-scale specimens based on scaled wind tunnel experiments. Existing machine learning approaches in the wind engineering domain are incapable of accurately extrapolating the prediction from scaled data to full-scale data. The model presented in this research, on the other hand, is capable of extrapolating prediction from large-scale or small-scale models to full-scale measurements. The proposed ML model combines a few-shot learning model with the existing physical knowledges in the design standards related to the zonal information. This physical information helps in clustering the few-shot learning model and improves prediction performance. Using the proposed techniques, the scaling issue observed in wind tunnel tests can be partially resolved. A low mean-squared error, mean absolute error, and a high coefficient of determination were observed when predicting the mean and standard deviation wind pressure coefficients of the full-scale dataset. In addition, the benefit of incorporating physical knowledge is verified by comparing the results with a baseline few-shot learning model. This method is the first of its type as it is the first time to extrapolate in wind performance prediction by combining prior physical knowledge with a few-shot learning model in the field of wind engineering. With the benefit of the few-shot learning model, only a low-resolution of the measuring tap configuration is required, and the reliance on physical wind tunnel experiments can be reduced. The physics-informed few-shot learning model is an efficient, robust, and accurate alternate solution to predicting wind pressures on full-scale structures based on various modeled scale experiments.

Towards a Wind Urbanism in Tropical Environments

One of the conditions for the proper functioning of passive comfort in humid tropical environments is access to natural ventilation in buildings. This notion of access to natural ventilation has taken on its full meaning during the current health crisis.
 Based on this observation established by a rich literature, we asked ourselves how to ensure the sustainability of the good functioning of natural ventilation in a humid tropical environment of a building in a built complex? This questioning led us to show the importance of the context through various dimensions: the chain of natural ventilation, the programmatic context, the climatic and geographical context, the regulatory context.
 Taking these parameters into account has allowed us, in the context of a case study, the eco-district Cœur de ville de La Possession, on the island of La Réunion, to develop a new conceptual approach associating urban planning and aeraulic engineering from the beginning of the design process for maximum efficiency.
 To this end, we initiated a new approach based on: co-design, the use of physical wind tunnel simulation at different scales, the integration of environmental, architectural and landscape recommendations at the scale of the district and of the buildings making up this district, in an enforceable urban planning regulation. This has enabled us, within the framework of this eco-district, to develop the concept of the right to natural ventilation, of the windy city and of the guarantee over time of the preservation of this potential.
 The transcription of this approach in other eco-neighbourhoods in a tropical environment seems to us to be a major challenge to be considered and which could even be extended to other climatic zones, in the context of current global warming.

Optimization of complex-geometry high-rise buildings based on wind load analysis

As technology advances, architects often employ innovative, non-standard shapes in their designs for the fast-growing number of high-rise buildings. Conversely, climate change is bringing about an increasing number of dangerous wind events causing damage to buildings and their surroundings. These factors further complicate the already difficult field of structural wind analysis. Current methods for calculating structural wind response, such as the Eurocode, do not provide methods for unconventional building shapes or, in the case of physical wind tunnel test and in-depth computational fluid dynamics (CFD) simulation, they are prohibitively expensive and time-consuming. Thus, wind load analysis is often relegated to late in the design process. This paper presents the development of a computational method to analyze the effect of wind on the structural behavior of a 3D building model and optimize the external geometry to reduce those effects at an early design phase. It combines CFD, finite-element analysis (FEA), and an optimization algorithm in the popular parametric design tool, Grasshopper. This allows it to be used in an early design stage for performance-based design exploration in complement to the more traditional late-stage methods outlined above. After developing the method and testing the timeliness and precision of the CFD, and FEA portions on case study buildings, the tool was able to output an optimal geometry as well as a database of improved geometric options with their corresponding performance for the wind loading.

Machine learning-based wind pressure prediction of low-rise non-isolated buildings

This paper proposes a novel machine learning-based wind pressure prediction model (ML-WPP) for low-rise non-isolated buildings. ML-WPP combines a gradient boosting decision tree (GBDT) and the Grid search algorithm (GSA) to automatically predict the wind pressure parameters. In comparison with existing ML models, this model is more straightforward and interpretable. The Tokyo Polytechnic University (TPU) non-isolated low-rise wind tunnel dataset is used to develop and test the ML-WPP model. ML-WPP considers the mean pressure coefficient, fluctuating pressure coefficient, and peak pressure coefficient to reflect the wind pressure among the roof area. The ML-WPP model obtained a low mean-squared error and a high coefficient of determination for all wind tunnel test configurations of the non-isolated low-rise buildings. A time history interpolation is proposed in this paper as well. This technique is the first of its kind as it is the first time an ML model has been used in the wind engineering field to deal with wind pressure prediction while considering the effect of the neighboring buildings. With the advantages of ML-WPP, it is possible to reduce the reliance on physical wind tunnel tests. ML-WPP yields a robust, efficient, accurate alternative to predicting the pressure of structures under wind loads while considering the effects of neighboring structures.

An architectural building cluster morphology generation method to perceive, derive, and form based on cyborg-physical wind tunnel (CPWT)

Rapid deduction based on environmental data has become a key factor influencing the early stages of conceptual design decisions. Traditional wind tunnels and CFD computational tools are time-consuming and number-limited of assumptions in iterative design, hence both are more commonly used in post-evaluation. With the development of artificial intelligence, this paper presented a new cyborg-physical wind tunnel (CPWT) design platform. By combining a customized physical wind tunnel with an optimization algorithm, a large amount of physical data can be quickly derived, and evaluations and predictions can be made.This paper first introduces the concepts of wind environment performance-based design including the physical platform design and the sensing system. The design methodology is reviewed in three sections: deduction framework, optimization goal, and evaluation indicator. Then, the paper proposed a new wind tunnel device, the CPWT, which incorporates 120 dynamic lifting units equipped with sensor, Arduino, and servomotor to capture wind data and generate real-time responses. Artificial neural network is integrated in the experiment to train on data like the windward area index and staggering index for the morphology generation. The result demonstrated that the mean square error is able to quickly stabilize to the range of [-0.02783, 0.02892] and [-2.324, 2.845], which achieved a lower data error and a better result predictability. The enhanced sensibility and real-time feedback are able to provide a more rapid method for the wind environment performance-based design in this digital age.

Inclusion of the physical wind tunnel in vehicle CFD simulations for improved prediction quality

When performing numerical simulations of the aerodynamic properties of vehicles, the simulation domain used is often a large box with a very low blockage ratio and a fully moving ground plane, replicating open road conditions. However, the physical measurements to which the simulation results are usually compared are typically performed in wind tunnels, with deficiencies concerning blockage, ground modeling, and other boundary interference effects. Some of these effects can be corrected for, but such corrections are usually performed on a global level and thus fail to correct for local effects that might influence different configurations of the vehicle in different ways. In this work, the typical open road numerical setup is compared to simulations where the computational domain is a virtual model of the complete slotted wall wind tunnel test section geometry. A vehicle of sedan type is simulated in different configurations, and the simulation results are compared to forces and pressure measurements from physical tests. The results show that the absolute drag coefficient can be predicted with very good accuracy by simulating the car inside the wind tunnel if compared to uncorrected measurement data. However, despite the good agreement for drag, the prediction of lift is not as satisfactory.

CFD Analysis of Hot Air Recirculation in Cooling System of Off Road Vehicle

The demands on cooling system of an off-road vehicle have increased due to charge air cooling, air conditioning and higher horsepower (hp) engines. In order to maximize cooling system performance of an off-road vehicle, the temperature of air entering the cooling system through front grill should be as low as possible, ideally at ambient temperature. Hot air exiting the cooling system which finds its way back to the front grill decreases the system performance. This is called as hot air recirculation. To study hot air recirculation complete vehicle is placed in physical wind tunnel facility. With CFD simulation tool this hot air recirculation can be studied in a virtual wind tunnel. Current paper studies hot air recirculation & quantifies the recirculation using CFD tool. Influence of tail wind velocity on recirculation was studied. The results of simulations were compared with experimental results.

Optimal design of structures using cyber-physical wind tunnel experiments with mechatronic models

This paper explores the use of a cyber-physical systems (CPS) approach to optimize the design of rigid, low-rise structures subjected to wind loading, with the intent of producing a foundational method to study more complex structures through future research. The CPS approach combines the accuracy of physical wind tunnel testing with the ability to efficiently explore a search space using numerical optimization algorithms. The approach is fully automated, with experiments executed in a boundary layer wind tunnel (BLWT), sensor feedback monitored by a computer, and actuators used to bring about physical changes to a mechatronic structural model. Because the model is undergoing physical change as it approaches the optimal solution, this approach is given the name “loop-in-the-model” optimization.Proof-of-concept was demonstrated for a low-rise structure with a parapet wall of variable height. Parapet walls alter the location of the roof corner vortices, reducing suction loads on the windward facing roof corners and edges and setting up an interesting optimal design problem. In the BLWT, the parapet height was adjusted using servo-motors to achieve a particular design. Experiments were conducted at the University of Florida Experimental Facility (UFEF) of the National Science Foundation's (NSF) Natural Hazard Engineering Research Infrastructure (NHERI) program.

A parametric study on the influence of boundary conditions on the longitudinal pressure gradient in CFD simulations of an automotive wind tunnel

Computational fluid dynamics (CFD) is an important and extensively used tool for aerodynamic development in the vehicle industry today. Validation of virtual methods by comparison to wind tunnel experiments is a must because manufacturers aim to substitute physical tests on prototype vehicles with virtual simulations. An appropriate validation can be performed only if the wind tunnel geometry with representative boundary conditions is included in the numerical simulation, and if the flow of the empty wind tunnel is accurately predicted. One of the important flow parameters to predict is the longitudinal pressure distribution in the test section, which is dependent on both the wind tunnel geometry and the settings of the boundary layer control systems. This study investigates the effects of flow angularity at the inlet and different boundary layer control systems, namely, basic scoop suction, distributed suction, and moving belts, on the longitudinal pressure distribution in the full-scale aerodynamic wind tunnel of Volvo Cars using CFD and a systematic design of experiments approach. The study shows that the different suction systems used to reduce boundary layer thickness upstream of the vehicle have statistically significant effects on the longitudinal pressure distribution in the test section. However, the estimated drag difference induced on a typical vehicle by the difference in horizontal buoyancy between the tested settings is within the test-to-test uncertainty of the physical wind tunnel, thereby leading to the conclusion that force calculations in simulations are fairly insensitive to the tested parameters on the investigated intervals.

Air pollutant dispersion around high-rise buildings under different angles of wind incidence

Gaseous pollutant originated from a building can disperse with ambient air flow and re-enter the same building under different environmental conditions. In our previous studies, it was revealed that the near-wall dispersion characteristics in a windward emission are significantly different from that in leeward emission for a high-rise building due to the effect of the building on the wind flow. Since the atmospheric wind changes constantly in both wind speed and wind direction, such that the wind rarely blows perpendicular to the front or the back of a building, it is important to investigate what occurs under different angles of wind incidence. By means of both physical wind tunnel measurement and simulations using Computational Fluid Dynamics (CFD), we firstly studied the dispersion characteristics around a square-sectioned building. It was found that the building influences on wind flow plays a significant role in the dispersion characteristics and an angle of wind incidence of about 90 degrees is a transition angle for the pollutant dispersion pathway around the building. For angles of wind incidence smaller than 90 degrees, air pollutant will migrate predominantly downward while for angles of wind incidence greater than 90 degrees, the pollutant will migrate predominantly upward. Further tests conducted on a more complicated crucifix-form building model with a re-entry along each building wing showed a similar trend of pollutant dispersion at different angles of wind incidence, with the transition angle shifted to approximately 75–80 degrees. The findings of this study show that building shape and the resultant wind-structure interaction plays a significant role in the pollutant dispersion around a building, thus influencing the air quality at different part of a building.

Wind tunnel testing and computational fluid dynamics in FLNG and floating production system design

Demonstrating how numerical modelling, such as computational fluid dynamics (CFD), can be used to validate results from detailed physical wind tunnel models of FLNG vessels and floating systems is the objective of this extended abstract. 3D rapid prototyping is used to build detailed physical wind tunnel models. This physical model (normally of an approximate scale of 1:200) is then placed in a wind tunnel facility to measure the time histories of the wind loads for a full range of wind directions and a range of drafts. CFD is then used to validate the wind tunnel modelling results. Numerical modelling can also be used to analyse a number of different issues such as the impact of turbine exhaust dispersion, and turbulence on helicopter operations and resulting helideck availability. This extended abstract discusses the importance of wind tunnel testing and numerical modelling during the design phase. The idea that numerical modelling does not replace pure theoretical or experimental results, but acts to complement them with gaining a greater overall picture, will be highlighted. Findings will be presented to discuss the advantages and disadvantages of both approaches, and highlight results such as wind shear and turbulence impacts being best calculated through wind tunnel testing. The extended abstract demonstrates that, ideally during the design process, wind tunnel testing should be followed by numerical modelling to interpolate results.

Influence of ventilation rate on the aerodynamic interference between two extra-large indirect dry cooling towers by CFD

Current wind-resistance designs of large-scale indirect dry cooling towers (IDCTs) exclude an important factor: the influence of the ventilation rate for radiator shutter on wind loads on the outer surfaces of the tower shell. More seemingly overlooked aspects are the effects of various ventilation rates on the wind pressure distribution on the tower surfaces of two IDCTs, and the feature of the flow field around them. In order to investigate the effects of the radiator shutter ventilation rates on the aerodynamic interference between IDCTs, this paper established the numerical wind tunnel model based on the Computational Fluid Dynamic (CFD) technology, and analyzed the influences of various radiator shutter ventilation rates on the aerodynamic loads acting upon a single and two extra-large IDCTs during building, installation, and operation stages. Through the comparison with the results of physical wind tunnel test and different design codes, the results indicated that: the influence of the ventilation rate on the flow field and shape coefficients on the outer surface of a single IDCT is weak, and the curve of mean shape coefficients is close to the reference curve provided by the current design code. In a two-tower combination, the ventilation rate significantly affects the downwind surface of the front tower and the upwind surface of the back tower, and the larger positive pressure shifts down along the upwind surface of the back tower as the ventilation rate increases. The ventilation rate significantly influences the drag force coefficient of the back tower in a two-tower combination, the drag force coefficient increases with the ventilation rate and reaches the maximum in a building status of full ventilation, and the maximum drag coefficient is 11% greater than that with complete closure.

Numerical Calculation of Wind Loads over Solar Collectors

For non-standard structures, such as parabolic trough collectors, the application of codes of practice to compute load coefficients usually results in oversized wind loads. Therefore, it is common practice to support the analysis experimentally with wind tunnel test results. This approach, however, is time-consuming, expensive, flow intrusive and requires a new set of tests for any modification in geometry, configuration, topography or load conditions, entailing additional time and expense. The results obtained are restricted to a finite set of points and variables, and most importantly, the size and wind velocities in available boundary layer wind tunnels impose Reynolds numbers well below those occurring in open air full-scale structures of this type. This similitude limitation prevents a direct and fully accurate extension of the results to the characterization of full scale collector structures. These wind tunnel shortcomings have positioned CFD as an appealing alternative for determining wind load distributions over solar collectors, solving most of these problems. Although extensively used in other applications, however, the application of CFD methods requires additional development, further testing and verification, proper modeling conditions and additional validation to gain acceptance as an alternative to physical wind tunnel tests.In this paper, CFD has been used as a “virtual” wind tunnel to compute the three-dimensional flow around a single model-scale module for a range of yaw and pitch angles, and the resultant load coefficients have been compared with those obtained experimentally in a physical wind tunnel. After validation against experimental data, the computational methodology has been applied to compute the wind loads on a full-scale module (including the complete supporting structure) and an array configuration of such modules. It will be shown that the relative mean errors of the numerical results with respect to the reference experimental data are within 10%, thus of the same order as experimental uncertainty.

Analysis of Aerodynamic Load Effect on Thin Plat Section in Multiple Fan Active Control Wind Tunnel

In atmospheric boundary, the power spectral density of turbulent wind simulated passively by the grid layer is regulated difficultly with the problem of smaller integral length of turbulence. For the advantage of active control method in adjusting the power spectral density and the integral length more simply, 11×9 multiple fan active control wind tunnel in Miyazaki University is utilized to debug many kinds of harmonic turbulent wind. Three-component aerodynamic forces on thin plat section (aspect ratio 22.5:1) in the harmonic turbulent wind field were measured by using the high frequency force balance of better stability and precision with testing the turbulent wind synchronously. The load effects on the model under different conditions, such as mean wind velocity, fluctuation frequency, turbulence intensity and integral length, were compared and analyzed. Frequency doubling amplification effect caused by the fixed wall boundary reflection effect in atmospheric boundary physical wind tunnel was reported and confirmed. In the validated effective frequency range where discrete frequency load effect caused by sinusoidal turbulent wind can be linearly superposed, the impacts on aerodynamic load effect induced by turbulence integral length and turbulence intensity were analyzed preliminarily. The differences between the conventional buffeting force theory and the wind tunnel test results of typical section model were clarified.

CFD wind tunnel test: Field velocity patterns of wind on a building with a refuge floor

This paper reports a CFD wind tunnel study of wind patterns on a square-plan building with a refuge floor at its mid-height level. In this study, a technique of using calibrated power law equations of velocity and turbulent intensity applied as the boundary conditions in CFD wind tunnel test is being evaluated by the physical wind tunnel data obtained by the Principal Author with wind blowing perpendicularly on the building without a refuge floor. From the evaluated results, an optimised domain of flow required to produce qualitative agreement between the wind tunnel data and simulated results is proposed in this paper. Simulated results with the evaluated technique are validated by the wind tunnel data obtained by the Principal Author. The results contribute to an understanding of the fundamental behaviour of wind flow in a refuge floor when wind is blowing perpendicularly on the building. Moreover, the results reveal that the designed natural ventilation of a refuge floor may not perform desirably when the wind speed on the level is low. Under this situation, the refuge floor may become unsafe if smoke was dispersed in the leeward side of the building at a level immediately below the refuge floor.

95/04158 Evaluation and quantification of the impact of cooling tower emissions on indoor air quality

Assessment of the potential impact of outdoor pollutant sources on indoor air quality through the reentrainment of pollutants vis-a-vis air-handling units, doorways, and windows has mainly focused on the evaluation of fume hood, boiler, diesel generator, and vehicular pollutant emissions. In recent years, however, gaseous and waterborne pollutants emitted from cooling towers have become an increasing source of concern. Chemicals such as biocides and corrosion and scale inhibitors are used to reduce and/or eliminate algae blooms, decrease bacterial and fungal growth, and reduce the corrosion of equipment. When added to the water used in cooling towers, these chemicals are emitted in both the gaseous phase and as pollutants dissolved in or suspended in water droplets. A qualitative evaluation of exhaust dispersion and droplet deposition rates associated with cooling towers is necessary when conducting an overall review of the environmental impact on indoor air quality. This paper identifies source emission rates to be used in assessing emissions of chemical additives in cooling towers, presents provisional design criteria for evaluating the impact of the chemical additives, and evaluates alternative methodologies for quantifying impact concentrations. These alternative assessment methodologies include numerical models, physical wind tunnel simulations, and computational fluid dynamics (CFD) simulations. Parameters more » used in comparing the methodologies include relative accuracy (order of magnitude) and modeling and simulation limitations. « less