Along and Across Wind Effects on Irregular Plan Shaped Tall Building

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.

A numerical study of wind loads on a semisubmersible platform is presented on this paper. The techniques of Computational Fluid Dynamics (CFD), such as Reynolds Averaged Navier-Stokes Equations (RANS) model and Large Eddy Simulation (LES), etc., were adopted in this study to predict wind loads on and wind flows around the platform. The main objective of this study is to explore an effective and reliable approach for evaluation of wind loads on offshore structures by CFD methods. The computed results were compared with experimental data which obtained at wind tunnel test. It was found through the comparison that the LES with a dynamic sub grid-scale (SGS) model can give satisfactory predictions for mean and dynamic wind loads on the tall structures. Therefore, it is necessary to correctly simulate both the incident wind velocity profile and turbulence intensity profile in CFD computations to accurately predict wind effects on huge structures. The recommend CFD techniques and associated numerical treatments provide an effective way for designers to assess wind effects on offshore platforms and the need for a detailed wind tunnel test.

During recent years, wind energy has moved from an emerging technology to a nearly competitive technology. This fact, coupled with an increasing global focus on environmental concern and a political desire of a certain level of diversification in the energy supply, ensures wind energy an important role in the future electricity market. For this challenge to be met in a cost-efficient way, a substantial part of new wind turbine installations is foreseen to be erected in big onshore or offshore wind farms. This fact makes the production, loading and reliability of turbines operating under such conditions of particular interest.

Volatilization of ammonia from field-applied animal slurry is a significant problem. Accurate emission measurements are needed for inventories and research, but are not provided by all measurement methods. Wind tunnels may give emission values substantially above or below micrometeorological results, which have been shown to be accurate. This limitation reduces the utility of wind tunnel results, which make up a large fraction of available measurements. The present work focused on understanding wind tunnel measurement error by comparing micrometeorological and wind tunnel measurements with the aid of a semi-empirical model. Ammonia loss from digestate after field application was measured in high time resolution in three field trials using wind tunnels and the backward Lagrangian stochastic (bLS) dispersion technique simultaneously. Differences in measured emission were interpreted using the ALFAM2 model, and measurements were used to evaluate the model. Results showed that wind tunnel and bLS methods provided different cumulative emission estimates, although there were similarities in measured emission dynamics. The ALFAM2 model was generally able to reproduce emission dynamics for both measurement methods, but only when differences in mass transfer between the two methods were incorporated in an experimental parameter set. This important result suggests that: 1) the simple structure of the ALFAM2 model captures the essential physical and chemical processes controlling emission and 2) the two measurement methods differ only (or mainly) through mass transfer above the slurry/soil surface and rain. Therefore, with careful selection of wind tunnel air flow it should be possible to approximately match emission that occurs under open-air conditions. But without temporal variation in air flow, actual emission dynamics cannot be captured. This work provides a template for integrating and comparing measurements from different methods, and suggests it is possible to use wind tunnel measurements for model evaluation and even parameter estimation.

A novel probabilistic approach is presented for estimating the equivalent static wind loads that produce a static response of the structure, which is equivalent in a probabilistic sense, to the extreme dynamic responses due to the unsteady pressure random field induced by the wind. This approach has especially been developed for complex structures (such as stadium roofs) for which the unsteady pressure field is measured in a boundary layer wind tunnel with a turbulent incident flow. The proposed method deals with the non-Gaussian nature of the unsteady pressure random field and presents a model that yields a good representation of both the quasi-static part and the dynamical part of the structural responses. The proposed approach is experimentally validated with a relatively simple application and is then applied to a stadium roof structure for which experimental measurements of unsteady pressures have been performed in boundary layer wind tunnel.

In order to evaluate the accuracy of computational fluid dynamics (CFD) for flow over a ship geometry, a comparison with an existing wind tunnel test of a simplified LHA hull with wind straight down the bow is made. One of the U.S. Navy's main interests in ship airwakes is the effect they have on aircraft operating nearby. In the interest of providing a more uniform flowfield in the vicinity of the ship, the wind tunnel test also investigates the effect of adding a downward -deflected flap to the bow, meant to mimic the rounded deck edge at the bow of later LHD -class ships, in contr ast to the sharp 90 -degree corner found on LHA - and earlier LHD -class ships. The CFD portion of this test also evaluates the effectiveness of the bow flap to show if CFD can match the trends of such geometry modifications. Furthermore, the CFD test investi gates the sensitivity of the solution to the grid resolution at the bow, where a large separation bubble affects a large portion of the flight deck, and will also determine if filtering the CFD data to mimic the performance of the wind tunnel equipment alt ers the results. This study seeks to validate CFD against wind tunnel data for this geometry and reinforce the wind tunnel assessment of the bow flap’s effectiveness. I. Introduction All branches of the U.S. military share an interest in the operation of air craft in the vicinity of ships. The airwake shed as wind flows over a ship can greatly influence the safety and ease of such operation. Features such as antennae, masts, radomes, deck equipment, and superstructures generate a complex flowfield that varies substantially with wind speed and direction. Due to the expense of repeating flight tests over different combinations of wind speed and direction, and with different aircraft types, CFD becomes an important tool in reducing such a test matrix by screening test conditions to those most crucial, and by evaluating ship geometries to predict problems and establish best design practices early in a ship's planning stage. To date, wind tunnels have borne much of the load for ship airwake testing, but they suffer f rom several drawbacks. Obviously, wind tunnels must use very small scale factors for ships, but they cannot achieve the airspeed required to match full -scale Reynolds numbers (Re). The small scale also decreases the period and size of pertinent flow featur es, making them difficult to detect. In addition, wind tunnel tests often require lengthy surveys or prior knowledge of the flowfield to find and adequately resolve off -body flow phenomena. In contrast, CFD can run any arbitrary physical scale, output resu lts at a user -determined frequency, and provide results over the entire solution space as a matter of course. However, wind tunnels certainly still provide an invaluable service in validating CFD and in testing conditions for which CFD is currently not sui table.

Comparison of wind tunnel and full-scale pressure measurement tests on the Texas Texh Building

Comparison of wind tunnel and full-scale pressure measurement tests on the Texas Texh Building

Comparison of Reynolds Averaging Navier-Stokes (RANS) turbulent models in predicting wind pressure on tall buildings

<div class="htmlview paragraph">Wind tunnel interference effects are still considered to be negligible - or at least undesired - in automotive aerodynamics. Consequently, up to now there is no standard correction method which is used in everyday wind tunnel testing although a lot of research has been done in recent years.</div> <div class="htmlview paragraph">In most full-vehicle CFD simulations, wind tunnel interference effects are not simulated. The flow about the car is computed under idealized conditions. The wind tunnel is designed to simulate these conditions but fails to do so to some degree due to its limited size.</div> <div class="htmlview paragraph">Therefore a comparison of blockage-free CFD results and wind tunnel measurements is deficient. Hence CFD simulations including wind tunnel interference effects should be favored in the future for validation purposes. Furthermore, CFD offers new possibilities to investigate individual contributions to wind tunnel interference effects and therefore could help to increase the understanding of the flow in the wind tunnel. This may result in the development of advanced correction methods. To be able to use these possibilities, it has to be ensured that all effects of the whole wind tunnel test section with a car present will be captured in a simulation.</div> <div class="htmlview paragraph">In this paper simulations of the IVK model scale wind tunnel including wind tunnel interference effects are presented. As a first parameter variation, the influence of different longitudinal pressure distributions in the virtual test section are investigated and compared with test data. This investigation is presented here. In a second step, different vehicle models will be tested. All simulations were carried out with EXA PowerFLOW™.</div>

Structural monitoring of an instrumented experimental single-storey wood building provided important information regarding the behaviour and response of low-rise buildings subjected to wind loads. Foundation wind-induced loads were captured by twenty-seven three-dimensional load cells simultaneously with the envelope pressures and weather characteristics. The distribution of the total wind load to each wall is examined and normalized to the wind speed for each direction. The correlation between loads acting on different wall segments is also quantified in the form of participation factors. In parallel with full-scale findings, a scaled model of the experimental building and its surroundings is tested in a boundary layer wind tunnel. The detailed pressure distribution information for thirty-six wind angles of attack obtained through three different upstream terrain simulations is used to generate expected total uplift wind force. The findings are compared to data acquired directly from the foundation load cells located in the test house. The comparison revealed that in most cases wind tunnel values are within the range of the field results. Discrepancies are somewhat higher for wind tunnel tests conducted using the open/suburban terrain compared to the urban terrain simulation. The results are significant for the improvement of the wind tunnel testing and simulation procedures, for the development of code and standard provisions, as well as for the verification of the finite element numerical model of the test house.

Validation of ADMS against wind tunnel data of dispersion from chemical warehouse fires

Paper deals with problems of CFD simulating airflow over a dimpled spherical surface and its verification by the wind tunnel measurement. The low-cost simulation approach was applied to be run on a common PC using the commercial software ANSYS CFX. The wind tunnel testing has been performed in the laboratory of aerodynamics at the Department of Air Force and Aircraft Technology of the University of Defence. Measured results of the drag coefficient versus the Reynolds number for smooth and dimpled spheres were compared and discussed. Presented simulation corresponds adequately to the experimental results. It can be stated that the CFD simulation is suitable for simulating the flow over the dimpled surfaces similar to sphere.

Wind loads on structures and the wind environment around buildings are based on tests in boundary layer wind tunnels with corresponding scale parameters. The lower part of the troposphere boundary layer was simulated inside a small wind tunnel located at the Wind Engineering Centre of the Université de Moncton. The correct scale ratios of the boundary layer thickness combined with the roughness height are two of the most important scales to match. For small wind tunnels, roughness parameters related to the model boundary layer can be difficult to measure since scale ratios for wind load studies are expected to be in the range of 400–1000. Oil-film interferometry was used to determine the roughness parameters (shear stress, friction velocity, and roughness height) of the forced turbulent boundary layer inside the wind tunnel. In this work, the International Organization for Standardization (ISO) Guide to Expression of Uncertainty in Measurements was used to evaluate the standard uncertainty of the roughness parameters on the bottom wall of the wind tunnel. The standard uncertainty of the roughness parameters depends strongly on the oil viscosity and on the accurate measurement of the fringe spacing. Results show that the standard uncertainty of the shear stress and friction velocity determined by the interferometry technique can be less than 5% when the oil viscosity and the fringe spacing can be accurately measured with a standard uncertainty lower than 4% and 1%, respectively.

An information exchange framework between physical modeling and numerical simulation to advance tropical cyclone boundary layer predictions