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Computation of wind pressures on low-rise structures
Abstract
This report describes the use of some computer programs written by one of the authors (DP) in predicting mean and peak wind pressures on arched-roof buildings. The research was carried out because there is a lack of good wind-tunnel and full-scale data on arched-roof buildings. The programs have been validated by comparing the results with wind-tunnel and full-scale data associated with the Texas Tech building.
... Some examples are: Hanson et al. (1986), Matthews (1987), Mochida et al. (1993), , . Paterson and Holmes (1992) analysed the wind flow around arched-roof buildings. The results were validated with the benchmark experiments performed on the Texas Tech building which provided a good understanding of the complex nature of wind flow around different shapes. ...
An accurate CFD modelling of wind flow around a city is important for a large variety of application. CFD simulations are heavily influenced by the large number of computational parameters defined in the model. This article presents a thorough and broad sensitivity study of the impact of computational parameters on the numerical outcome for wind flow pattern of a tropical city. In this current study, a series of 3D steady state RANS simulations are conducted in full scale for a region in the city with CFD software OpenFOAM. As CFD simulations are influenced by the computational parameters including turbulence models, for accurate wind flow modelling different turbulent models are tested. The numerical outcomes are compared with on-site measured data which are obtained from anemometers placed at different locations and heights within the downtown of the tropical city for a 2-year period. The impact of a variety of computational parameters is considered which include the mesh resolution and different turbulence models. The test for turbulence models shows that SST k-ω returns the most accurate result among other examined models compared to experimental data. A pedestrian comfort map is then derived based on extended land beaufort scale table and velocity field data from CFD. The result is consistent with long-term observations. In addition, vertical profile of the wind speed near every corner of some interested buildings is investigated for the potential installation of micro wind turbines
... The discrepancy observed at top elevation of 174 m could partially be attributed to the relatively complex 3-D turbulent flow structure involving more severe impinging and separations, which cannot be fully captured by the hybrid RANS-KS method. It is worth noting that Selvam (1992) and Paterson and Holmes (1992) developed an empirical equation to calculate the rms of pressure based on the Texas Tech building. Since the empirical equation is developed from the wind tunnel and full-scale measurement data of low-rise building, its applicability and application to high-rise building are worth further study. ...
Up till recent years, predicting wind loads on full-scale tall buildings using Large Eddy Simulation (LES) is still impractical due to a prohibitively large amount of meshes required, especially in the vicinity of the near-wall layers of the turbulent flow. A hybrid approach is proposed for solving pressure fluctuations of wind flows around tall buildings based on the Reynolds Averaged Navier–Stokes (RANS) simulation, which requires coarse meshes, and the mesh-free Kinematic Simulation (KS). While RANS is commonly used to provide mean flow characteristics of turbulent airflows, KS is able to generate an artificial fluctuating velocity field that satisfies both the flow continuity condition and the specific energy spectra of atmospheric turbulence. The kinetic energy is split along three orthogonal directions to account for anisotropic effects in atmospheric boundary layer. The periodic vortex shedding effects can partially be incorporated by the use of an energy density function peaked at a Strouhal wave number. The pressure fluctuations can then be obtained by solving the Poisson equation corresponding to the generated velocity fluctuation field by the KS. An example of the CAARC building demonstrates the efficiency of the synthesized approach and shows good agreements with the results of LES and wind tunnel measurements.
... The separation bubble with the wind perpendicular to the long side of the building was 1.04 m [ranging from 0.73 -1. Efforts have been made to model the WERFL building and reasonable results have been obtained with moderate grid sizes using k-ε turbulence models [3,7,8,9]. In these studies, pressure profiles over the length of the building were used as an indicator of the accuracy of the numerical model. ...
The purpose of this study is to resolve accurate, local flow details around buildings in an urban environment using commercial computational fluid dynamic (CFD) software. At present, few recommendations have been published regarding the appropriate turbulence models to be used for modelling these flow conditions. Due to the uncertain reliability of the k-ε models ability to successfully simulate flow over buildings, the current objective is to assess how applicable the k-ε turbulence model is in resolving this type of flow. Flow around buildings in the atmospheric boundary layer are characterized as having points of separation, reattachment, stagnation and various types of vortices as well as being anisotropic and transient in nature. The complexity of this problem indicates that the turbulence model must be capable of handling many issues to correctly model this flow. In order to justify an applicable turbulence model, these models must be tested under relatively simple conditions and compared with well-documented, large-scale tests to ensure accuracy. The standard k-ε model was investigated in these conditions because of its relative robustness and past ability to capture the major flow details in this type of flow. Increasing the number of cells in the domain had various effects on the solution. An accurate solution was obtained for the initial mesh and then subsequently the solution diverged and then converged when refining the mesh. Very fine grids were required for a two-dimensional building to achieve accurate results, but the solution was not verified as being grid independent. Even if the solution is grid independent, implementation of the k-ε model in three-dimensional complex flows would not be practical due to the substantial increase in computational power required. Therefore alternative turbulence models are now being investigated for modelling flow over buildings in the atmospheric boundary layer.
This paper presents three-dimensional numerical simulation of wind flows around and pressures on building surfaces for different wind directions. The computational procedure includes solving the time-averaged Navier-Stokes equations with the help of a modified k-e turbulence model. The control volume method is used for numerical discretization. Computer programs have been developed to simulate three-dimensional turbulent flow over buildings on staggered rectangular grid system. In this paper, computational predictions of the surface pressures on the Texas Tech University Building are compared with the full scale and wind tunnel measurements. A very good level of agreement is obtained for mean and fluctuating pressures. The predicted fluctuating pressures on the surfaces of the building by the present computation are in better agreement with the field data than those obtained in the wind tunnel tests.
The airflow rate through a two-story building with a courtyard, with and without trees, was estimated and compared with that of a building without a courtyard. The building and the courtyard were of square shapes, each 10 m to the side. The courtyard walls were 3m high and two separate trees of spherical, cylindrical and conical shapes were considered in the yard. The courtyard was directly south of the building and a wind angle of zero degree was considered when the wind was blowing directly from the south. It was found that when the wind angles were between 0 to ±90 degrees, the airflow rate through the building was reduced when compared with the building without a courtyard. The presence of trees in the courtyard further reduced the airflow rate. When the wind angle was 180 degrees, i.e., when the courtyard was in the lee-ward side of the wind, the airflow rate through the building was increased, and the presence of the trees in the courtyard further increased the flow rate. By considering the wind speeds and directions for the cities of Ahwaz, Kerman, Mashad, Shiraz, Tabriz and Tehran, Iran, the airflow rates were estimated for the buildings located in these cities. The effect of a courtyard and its trees in reducing the airflow rates (or increasing it, under special wind directions) were then determined.
Data from full-scale building tests conducted in Texas Tech University are used to quantify the uncertainties associated with the use of computational fluid dynamics to obtain wind load predictions for full-scale structures. It is demonstrated that the effects of computational domain is relatively small, and the effects of grid arrangement, turbulence model and inlet boundary condition are relatively obvious. Finally, guidelines are suggested for reasonable design and suitable choice of turbulence model.
The subject of this paper pertains to an apparently well researched area. A good number of research efforts the world over have involved for decades the determination of wind loads on low rise buildings. However, the subject continues to be a live area of enquiry. There are several reasons for it. A rather large number of factors affect wind loads on low rise buildings, besides also the wide range of the variables involved. Furthermore, it is true that a vast majority of buildings fall under the category of “low-rise”. Research has produced new and important information which is relevant to the safety of engineering constructions, and even more to the millions of partially-engineered ones. Two earlier works by Stathopoulos [1] and Holmes [2] made a review on the subject. This paper covers a wider scope and attempts to put together the state-of-the-art of the information available.
The paper reviews the current state of the art in computational wind engineering, particularly as it relates to applications of numerical flow modelling for the evaluation of wind effects on buildings and their environment. The variability of computational results is presented and compared with that of wind tunnel measurements. Concerns are expressed regarding the current application of the numerical approach in the design practice in cases for which the computational results may not be adequate. Future challenges regarding the improvement of computational wind engineering methodologies are discussed and the importance of identifying resolution and numerical errors is emphasized.
In this paper results from a computer simulation of wind flows around prismatic bodies using a k-ϵ model of turbulence are compared with full scale and wind tunnel tests done by others. The agreement is good, both in the wake region and elsewhere, and is particularly good for flow around a cube in which the overall error level in both pressures and velocities is about 5–10%. This is comparable with the error achievable with well controlled wind tunnel tests.
The full-scale test building at Texas Tech University represents one of the best instrumented full-scale installations for determining wind loads on low buildings. In particular, it is intended to provide data of the highest quality for comparison with and verification of model scale experiments. In advance of full-scale data from the test building, a model scale experiment was undertaken to define the characteristics of the local pressures, partly to aid in the definition of the full-scale experiment and partly to provide an “unbiased” set of pressures for comparison. This paper describes the model and documents the test procedures in which results were determined for two simulated terrain roughnesses. Representative wind tunnel results are presented, and some comparisons are included with the first reliable data available from the full-scale experiment.
A computer program has been developed to compute turbulent flows over three-dimensional rectangular surface-mounted bluff bodies and the results have been applied to wind flows over buildings. The program solves the steady-state Reynolds equation using a κ—ϵ model of turbulence. The resulting differential equations are solved by the use of the SIMPLE algorithm.Four flows have been studied and the computed results compared with full scale and wind tunnel measurements carried out by others. Good agreement has been obtained in most cases.
Early results from the field experiment at Texas Tech University to determine wind pressures on a low-rise building are reported. The capability to rotate the building has provided useful, consistent ensembles of 15-min records for two angles-of-attack: 90° (wind normal to the long walls) and 60°. Mean, rms and peak pressure coefficients are presented for 11 points on the walls and roof along the centerline of the building. Mean wind speed, turbulence intensity, power-law exponent and roughness length data are given for use in wind tunnel testing. The design of the reference pressure system and the effects of moving average filters on the peak pressures are also discussed.
TEACH-T: A general computer program for two-dimensional, turbulent, recirculating flows
- A D Gosman
- F J K Ideriah
Gosman, A.D. and Ideriah, F.J.K. 1976, 'TEACH-T: A general computer
program for two-dimensional, turbulent, recirculating flows', Department of
Mechanical Engineering, Imperial College, London.
SAA Loading Code, Part 2 Wind loads
- Standards Australia
- M L Levitan
- J D Holmes
- K C Mehta
- W P Vann
Levitan, M.L., Holmes, J.D., Mehta, K.C. and Vann, W.P. 1989, 'Fieldmeasured pressures on the Texas Tech Building', 8th Colloq. Indust. Aerodyn.,
Aachen, W.Germany, 4-7 Sept.