Abstract
The present situation of CWE(Computational Wind Engineering) and the papers presented tornthe CWE 2000 Symposium are reviewed from the following viewpoints; 1) topics treated, 2) utilization ofrncommercial code (software), 3) incompleteness of CWE, 4) remaining research subjects, 5) predictionrnaccuracy, 6) new fields of CWE application, etc. Firstly, new tendencies within CWE applications are indicated.rnNext, the over-attention being given to the application field and the lack of attention to fundamentalrnproblems, including prediction error analysis, are pointed out. Lastly, the future trends of CFD (ComputationalrnFluid Dynamics) applications to wind engineering design are discussed.
Key Words
Address
Shuzo Murakami, Faculty of Science and Technology, Keio University, Kanagawa, Japan
Abstract
Accidental gaseous losses from industrial processes can pose considerable health andrnenvironmental risks but assessing their health, safety and environmental impact is problematic. Improvedrnunderstanding and simulation of the dispersion of emissions in the vicinity of storage tanks is required.rnThe present study aims to assess the capability of the turbulence closures and meshing alternatives in arncommercially available CFD code for predicting dispersion in the vicinity of cubes and circular cylindricalrnstorage tanks. The performance of the k- e and Reynolds Stress turbulence models and meshing alternativesrnfor these cases are compared to experimental data. The CFD simulations are very good qualitatively and,rnin many cases, quantitatively. A mesh with prismatic elements is more accurate than a tetrahedral mesh.rnOverall the Reynolds stress model performs slightly better than the k- e model.
Key Words
CFD; near-field dispersion modelling; circular cylinders; storage tanks.
Address
C. E. Fothergill and P. T. Roberts, Shell Research Ltd., P.O. Box 1, Cheshire, CH1 3SH, U.K.rnA. R. Packwood, School of Mechanical and Materials Engineering, University of Surrey, Guildford, GU2 5XH, U.K.
Abstract
Both a Finite Volume and a Discrete Vortex technique to solve the unsteady Navier-Stokesrnequations have been employed to study the air flow around long-span bridge decks. The implementationrnand calibration of both methods is described alongside a quasi-3D extension added to the DVM solver.rnApplications to the wind engineering of bridge decks include flow simulations at different angles ofrnattack, calculation of aerodynamic derivatives and fluid-structure interaction analyses. These are beingrnpresented and their specific features described. If a numerical method shall be employed in a practicalrndesign environment, it is judged not only by its accuracy but also by factors like versatility, computationalrncost and ease of use. Conclusions are drawn from the analyses to address the question of whetherrncomputer simulations can be practical design tools for the wind engineering of bridge decks.
Abstract
A mesoscale meteorological model is applied to simulate turbulent airflow and eddy sheddingrnover the Isle of Arran, SW Scotland, UK. Under conditions of NW flow, the mountain ridge of Kintyre,rnlocated upwind of Arran, induces gravity waves that also affect the airflow over the island. The possibilityrnto nest domains allows description of the airflow over Arran with a very high resolution grid, while alsornincluding the effects of the surrounding mainland of Scotland, in particular of the mountain ridge ofrnKintyre. Initialised with a stably stratified NW flow, the mesoscale model simulates quasi-stationaryrngravity waves over the island induced by Kintyre. Embedded in the larger scale wave trains there isrncontinuous development of small-scale transient eddies, created at the Arran hill tops, that move downstreamrnthrough the stationary wave field. Although the transient eddies are more frequently simulated on thernnorthern island where the terrain is more pronounced, they are also produced over Tighvein, a hill of 458rnm on the southern island where measurements of surface pressure and 2 m meteorological variables havernbeen recorded at intermittent intervals between 1996 and 2000. Comparison between early observationsrnand simulations so far show qualitatively good agreement. Overall the computations demonstrate thatrnturbulent flow can be modelled with a horizontal resolution of 70 m, and describe turbulent eddy structurernon wavelength of only a few hundred metres.
Key Words
rotors; reverse flow; high resolution; modelling over steep terrain.
Address
J. Thielen and A. Gadian, Physics Department, UMIST, Manchester M60 1QD, UKrnS. Vosper and S. Mobbs, School of Environment, University of Leeds, Leeds, UK
Abstract
This paper presents some of the results of a project whose aim has been to produce a fullrnsimulation model which would determine the efficacy of pesticides for use by both farmers and thernbio-chemical industry. The work presented here describes how crop architecture can be mathematicallyrnmodelled and how the mechanics of pesticide droplet capture can be simulated so that if a wind assistedrndroplet-trajectory model is assumed then droplet deposition patterns on crop surfaces can be predicted.rnThis achievement, when combined with biological response models, will then enable the efficacy of pesticidernuse to be predicted.
Address
S. J. Cox and D. W. Salt, School of Mathematics and Statistics, University of Portsmouth, Portsmouth PO1 3QL, U.K.rnB. E. Lee, Department of Civil Engineering, University of Portsmouth, Portsmouth PO1 3QL, U.K.rnM. G. Ford, School of Biological Sciences, University of Portsmouth, Portsmouth PO1 3QL, U.K.
Abstract
Numerical simulations based on the ALE finite element method are carried out to examinernthe aerodynamics of an oscillating circular cylinder when the separated shear flows around the cylinderrnare stimulated by periodic jet excitation with a shear layer instability frequency. The excitation is appliedrnto the flows from two points on the cylinder surface. The numerical results showed that the excitationrnwith a shear layer instability frequency can reduce the negative damping and thereby stabilize thernaerodynamics of the oscillating cylinder. The change of the lift phase seems important in stabilizing therncylinder aerodynamics. The change of lift phase is caused by the merger of the vortices induced by thernperiodic excitation with a shear layer instability frequency, and the vortex merging comes from the highrngrowth rate, the rapid increase of wave number and decrease of phase velocity for the periodic excitationrnin the separated shear flows.
Key Words
ALE; aerodynamic instability; circular cylinder; finite element method; periodic excitation; separated shear layer; shear layer instability; vortex-induced vibration.
Address
S. Hiejima, Department of Environmental & Civil Engineering, Faculty of Environmental Science and Technology, Okayama University, 1-1, Tsushima-Naka, 3-chome, Okayama 700-8530, JapanrnT. Nomur a, Department of Civil Engineering, College of Science and Technology, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan
Abstract
Predictions of the pedestrian level wind speeds for the downtown area of Auckland that havernbeen obtained by wind tunnel and computational fluid dynamic (CFD) modelling are presented. The windrntunnel method involves the observation of erosion patterns as the wind speed is progressively increased.rnThe computational solutions are mean flow calculations, which were obtained by using the finite volumerncode PHOENICS and the k- e turbulence model. The results for a variety of wind directions are compared, andrnit is observed that while the patterns are similar there are noticeable differences. A possible explanationrnfor these differences arises because the tunnel prediction technique is sensitivity to gust wind speeds whilernthe CFD method predicts mean wind speeds. It is shown that in many cases the computational modelrnindicates high mean wind speeds near the corner of a building while the erosion patterns are consistent withrneddies being shed from the edge of the building and swept downstream.
Key Words
pedestrian winds; computational modelling.
Address
P. J. Richards, G. D. Mallinson, D. McMillan and Y. F. Li, Department of Mechanical Engineering, The University of Auckland, Private Bag 92019,rnAuckland, New Zealand
Abstract
Results of measurements of surface pressure and of velocity field made on a full-scale 6 mrncube in natural wind are reported. Comparisons are made with results from boundary-layer wind-tunnelrnstudies reported in the literature. Two flow angles are reported; flow normal to a face of the cube (the 0 orncase) and flow at 45 o . In most comparisons, the spread of wind-tunnel results of pressure measurementsrnspans the full-scale measurements. The exception to this is for the 0 o case where the roof and side-wallrnpressures at full-scale are more negative, and as a result of this the leeward wall pressures are also lower.rnThe cause of this difference is postulated to be a Reynolds Number scale effect that affects flow reattachment.rnMeasurements of velocity in the vicinity of the cube have been used to define the mean reattachmentrnpoint on the roof centre line for the 0 o case, and the ground level reattachment point behind the cube forrnboth 0 o and 45 o flow. Comparisons are reported with another full-scale experiment and also with wind-tunnelrnexperiments that indicate a possible dependency on turbulence levels in the approach flow.
Key Words
full-scale; wind; pressure; velocity; cube; wind-tunnel.
Address
R. P. Hoxey, P. J. Richards and J. L. Short, Silsoe Research Institute, Wrest Park, Silsoe, Bedford, MK45 4HS, U.K.
Abstract
Computation solutions for the flow around a cube, which were generated as part of thernComputational Wind Engineering 2000 Conference Competition, are compared with full-scale measurements.rnThe three solutions shown all use the RANS approach to predict mean flow fields. The major differencesrnappear to be related to the use of the standard k- e, the MMK k- e and the RNG k- e turbulence models.rnThe inlet conditions chosen by the three modellers illustrate one of the dilemmas faced in computationalrnwind engineering. While all modeller matched the inlet velocity profile to the full-scale profile, only onernof the modellers chose to match the full-scale turbulence data. This approach led to a boundary layer thatrnwas not in equilibrium. The approach taken by the other modeller was to specify lower inlet turbulentrnkinetic energy level, which are more consistent with the turbulence models chosen and lead to a homogeneousrnboundary layer. For the 0 o case, wind normal to one face of the cube, it is shown that the RNG solutionrnis closest to the full-scale data. This result appears to be associated with the RNG solution showing therncorrect flow separation and reattachment on the roof. The other solutions show either excessive separationrn(MMK) or no separation at all (K-E). For the 45 o case the three solutions are fairly similar. None of themrncorrectly predicting the high suctions along the windward edges of the roof. In general the velocityrncomponents are more accurately predicted than the pressures. However in all cases the turbulence levelsrnare poorly matched, with all of the solutions failing to match the high turbulence levels measured aroundrnthe edges of separated flows. Although all of the computational solutions have deficiencies, the variabilityrnof results is shown to be similar to that which has been obtained with a similar comparative wind tunnelrnstudy. This suggests that the computational solutions are only slightly less reliable than the wind tunnel.
Key Words
computational wind engineering; cube; turbulence modelling.
Address
P. J. Richards and A. D. Quinn, Environment Group, Silsoe Research Institute, Wrest Park, Silsoe, Bedfordshire, MK45 4HS, U.K.rnS. Parker, Division of Environmental Health & Risk Management, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
Abstract
Previous studies have shown that Computational Wind Engineering (CWE) is still in itsrninfancy and has a long way to go to become truly useful to the design practitioner. The present workrnfocuses on more recent studies to identify progress on outstanding issues and improvements in thernnumerical simulation of wind effects on buildings. The paper reviews wind loading and environmentalrneffects; it finds that, in spite of some interesting and visually impressive results produced with CWE, thernnumerical wind tunnel is still virtual rather than real and many more parallel studies - numerical andrnexperimental - will be required to increase the level of confidence in the computational results.
Key Words
aerodynamics; computational fluid dynamics; design; pressure; velocity; wind.
Address
T. Stathopoulos, Centre for Building Studies, Concordia University, Montreal, H3G 1M8, Canada
Abstract
When predicting unsteady flow and pressure fields around a structure in a turbulent boundaryrnlayer by Large Eddy Simulation (LES), velocity fluctuations of turbulence (inflow turbulence), whichrnreproduce statistical characteristics of the turbulent boundary layer, must be given at the inflow boundary.rnHowever, research has just started on development of a method for generating inflow turbulence thatrnsatisfies the prescribed turbulence statistics, and many issues still remain to be resolved. In our previousrnstudy, we proposed a method for generating inflow turbulence and confirmed its applicability by LES ofrnan isotropic turbulence. In this study, the generation method was applied to a turbulent boundary layerrndeveloped over a flat plate, and the reproducibility of turbulence statistics predicted by LES computationrnwas examined. Statistical characteristics of a turbulent boundary layer developed over a flat plate wererninvestigated by a wind tunnel test for modeling the cross-spectral density matrix for use as targets ofrninflow turbulence generation for LES computation. Furthermore, we investigated how the degree ofrncorrespondence of the cross-spectral density matrix of the generated inflow turbulence with the targetrncross-spectral density matrix estimated by the wind tunnel test influenced the LES results for the turbulentrnboundary layer. The results of this study confirmed that the reproduction of cross-spectra of the normalrncomponents of the inflow turbulence generation is very important in reproducing power spectra, spatialrncorrelation and turbulence statistics of wind velocity in LES.
Key Words
LES; inflow turbulence; turbulent boundary layer; cross-spectral density matrix.
Address
K. Kondo and M. Tsuchiya, Kajima Technical Research Institute, 2-19-1, Tobitakyu, Chofu-shi, Tokyo 182-0036, JapanrnA. Mochida, Graduate School of Engineering, Tohoku Univ., Aoba 06, Sendai 980-8579, JapanrnS. Murakami, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
Abstract
Recently, the prediction of wind environment around a building using Computational FluidrnDynamics (CFD) technique comes to be carried out at the practical design stage. However, there havernbeen very few studies which examined the accuracy of CFD prediction of flow around a high-risernbuilding including the velocity distribution at pedestrian level. The working group for CFD prediction ofrnwind environment around building, which consists of researchers from several universities and privaterncompanies, was organized in the Architectural Institute of Japan (AIJ) considering such a background. Atrnthe first stage of the project, the working group planned to carry out the cross comparison of CFD resultsrnof flow around a high rise building by various numerical methods, in order to clarify the major factorsrnwhich affect prediction accuracy. This paper presents the results of this comparison.
Key Words
CFD; wind environment; revised k- e models; Durbin
Address
Graduate School of Engineering, Tohoku University, 06, Aoba, Sendai, Miyagi, 980-8579, JapanrnNiigata Institute of Technology, 1719, Fujibashi, Kashiwazaki-shi, Niigata, 945-1195, JapanrnKeio University, 3-14-1, Hiyoshi, Kita-ku, Yokohama-shi, Kanagawa, 223-8522, JapanrnMaeda Corporation, 1576-1, Tsukinowa, Namerikawa, Hiki-gun, Saitama, 355-0313, JapanrnGraduate School of Engineering, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8656, JapanrnInstitute of Industrial Science, University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo, 153-8505, Japan
Abstract
Two-dimensional formulations for wind forces on elongated bodies, such as bridge decks, arernreviewed and links with expressions found in two-dimensional airfoil theory are pointed out. The presentrnresearch focus on indicial lift responses and admittance functions which are commonly used to improvernbuffeting analysis of bluff bodies. A computational fluid dynamic (CFD) analysis is used to derive thesernaerodynamic functions for various sections. The numerical procedure is presented and results are discussedrnwhich demonstrate that the particular shapes of these functions are strongly dependent on the evolution ofrnthe separated flows around the sections at the early stages.
Key Words
indicial lift response; admittance function; buffeting forces; CFD; RNG k- e.
Address
Gregory Turbelin and Rene Jean Gibert, CEMIF - Universite d\'Evry Val d\'Essonne, 40 rue du Pelvoux, 91020 Evry Cedex, France
Abstract
In the recent years flow around bridges are investigated using computer modeling. Selvamrn(1998), Selvam and Bosch (1999), Frandsen and McRobie (1999) used finite element procedures. Larsenrnand Walther (1997) used discrete vorticity procedure. The aeroelastic instability is a major criterion to bernchecked for long span bridges. If the wind speed experienced by a bridge is greater than the critical windrnspeed for flutter, then the bridge fails due to aeroelastic instability. Larsen and Walther (1997) computedrnthe critical velocity for flutter using discrete vortex method similar to wind tunnel procedures. In thisrnwork, the critical velocity for flutter will be calculated directly (free oscillation procedure) similar to thernapproaches reported by Selvam et al. (1998). It is expected that the computational time required torncompute the critical velocity using this approach may be much shorter than the traditional approach. Therncomputed critical flutter velocity of 69 m/s is in reasonable comparison with wind tunnel measurement.rnThe no flutter and flutter conditions are illustrated using the bridge response in time.
Key Words
computational fluid dynamics; bridge aerodynamics; computational wind engineering; large eddy simulation; flutter analysis; wind loading.
Address
R. Panneer Selvam and S. Govindaswamy, BELL 4190, University of Arkansas, Fayetteville, AR 72701, USArnHarold Bosch, Aerodynamics Laboratory, FHWA, Georgetown Pike, McLean, VA 22101, USA
Abstract
Research being undertaken at the University of Auckland has enabled Vortec Energy tornimprove the performance of the Vortec 7 Diffuser Augmented Wind Turbine. Computational Fluid Dynamicrn(CFD) modelling of the Vortec 7 was used to ascertain the effectiveness of geometric modifications to thernVortec 7. The CFD work was then developed to look at new geometries, and refinement of these led torngreater power augmentation for a given diffuser exit area ratio. Both full scale analysis of the Vortec 7 andrna wind tunnel investigation of the development design have been used for comparison with the CFD model.
Address
D. G. Phillips, P. J. Richards and R. G. J. Flay, Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand
Abstract
A two dimensional discrete vortex method (DIVEX) has been developed at the Departmentrnof Aerospace Engineering, University of Glasgow, to predict unsteady and incompressible flow fieldsrnaround closed bodies. The basis of the method is the discretisation of the vorticity field, rather than thernvelocity field, into a series of vortex particles that are free to move in the flow field that the particlesrncollectively induce. This paper gives a brief description of the numerical implementation of DIVEX andrnpresents the results of calculations on a recent suspension bridge deck section. The results from both thernstatic and flutter analysis of the main deck in isolation are in good agreement with experimental data. Arnbrief study of the effect of flow control vanes on the aeroelastic stability of the bridge is also presentedrnand the results confirm previous analytical and experimental studies. The aeroelastic study is carried outrnfirstly using aerodynamic derivatives extracted from the DIVEX simulations. These results are thenrnassessed further by presenting results from full time-dependent aeroelastic solutions for the original deckrnand one of the vane cases. In general, the results show good qualitative and quantitative agreement with resultsrnfrom experimental data and demonstrate that DIVEX is a useful design tool in the field of wind engineering.
Address
I. Taylor, Department of Mechanical Engineering, University of Strathclyde, Glasgow, G11XJ, Scotland UK
M. Vezza, Department of Aerospace Engineering, University of Glasgow, Glasgow, G12 8QQ, Scotland, UK
Abstract
An efficient large eddy simulation algorithm is used to compute surface pressure distributionsrnon an eleven story (target) building on the NIST campus. Local meteorology, neighboring buildings,rntopography and large vegetation (trees) all play an important part in determining the flows and thereforernthe pressures experienced by the target. The wind profile imposed at the upstream surface of therncomputational domain follows a power law with an exponent representing a suburban terrain. This profilernaccounts for the flow retardation due to friction from the surface of the earth, but does not includernfluctuations that would naturally occur in this flow. The effect of neighboring buildings on the timerndependent surface pressures experienced by the target is examined. Comparison of the pressure fluctuations onrnthe single target building alone with those on the target building in situ show that, owing to vortices shedrnby the upstream buildings, fluctuations are larger when such buildings are present. Even when buildingsrnare lateral to or behind the target, the pressure disturbances generate significantly different flows aroundrnthis building. A simple grid-free mathematical model of a tree is presented in which the trunk and the branchesrnare each represented by a collection of spherical particles strung together like beads on a string. The dragrnfrom the tree, determined as the sum of the drags of the component particles, produces an oscillatory, spreadingrnwake of slower fluid, suggesting that the behavior of trees as wind breakers can be modeled usefully.
Key Words
computational fluid dynamics; computational wind engineering; large eddy simulations; tree(single) drag model.
Address
R. G. Rehm, K. B. McGrattan and H. R. Baum, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, U.S.A.
Abstract
An important goal of computational wind engineering is to impact the design process withrnsimulations of flow around buildings and bridges. One challenging aspect of this goal is to solve thernNavier-Stokes (NS) equations accurately. For the unsteady computations, an adaptive finite element techniquernmay reduce the computer time and storage. The preliminary application of a p-version as well as an h-versionrnadaptive technique to computational wind engineering has been reported in previous paper. Therndetails on the implementation of p-adaptive technique will be discussed in this paper. In this technique,rntwo posteriori error estimations, which are based on the velocity and vorticity, are first presented. Then,rnthe polynomial order of the interpolation function is increased continuously element by element until thernestimated error is less than the accepted. The second through sixth orders of hierarchical functions arernused as the interpolation polynomials. Unequal order interpolations are used for velocity and pressure.rnUsing the flow around a circular cylinder with Reynolds number of 1000 the two error estimators arerncompared. The result show that the estimated error based on the velocity is lower than that based onrnthe vorticity.
Key Words
computational fluid dynamics; adaptive finite element method; computational wind engineering.
Address
R. Panneer Selvam and Zu-Qing Qu, Computational Mechanics Laboratory, Department of Civil Engineering BELL 4190, University of Arkansas, Fayetteville, AR 72701, USA
Abstract
A numerical investigation on the turbulent flows over a three-dimensional steep hill isrnpresented. The numerical model developed for the present work is based on the finite volume method andrnthe SIMPLE algorithm with a non-staggered grid system. Standard k-ε model and Shih's non-linear model are tested for the validation of the prediction accuracy in the 3D separated flow. Comparisons of the mean velocity and turbulence profiles between the numerical predictions and the measurements show good agreement. The Shih's non-linear model is found to predict mean flow and turbulence better than the Standard k-ε. Flow patterns have also been examined to explain the difference in the cavity zone between 2D and 3D hills.
Address
Takeshi Ishihara, Department of Civil Engineering, University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8656, JapanrnKazuki Hibi, Wind Engineering Group, Institute of Technology, Shimizu Corp.,rn3-4-17, Etchujima, Koto-ku, Tokyo 135-8530, Japan
Abstract
The along-wind response of a surface-mounted elastic fence under the action of wind wasrninvestigated numerically. In the computations, two sets of equations, one for the simulation of thernunsteady turbulent flow and the other for the calculation of the dynamic motion of the fence, were solvedrnalternatively. The resulting time-series tip response of the fence as well as the flow fields were analyzedrnto examine the dynamic behaviors of the two. Results show that the flow is unsteady and is dominated byrntwo frequencies: one relates to the shear layer vortices and the other one is subject to vortex shedding.rnThe resulting unsteady wind load causes the fence to vibrate. The tip deflection of the fence is periodicrnand is symmetric to an equilibrium position, corresponding to the average load. Although the along-windrnaerodynamic effect is not significant, the fluctuating quantities of the tip deflection, velocity and accelerationrnare enhanced as the fundamental frequency of the fence is near the vortex or shedding frequency of thernflow due to the occurrence of resonance. In addition, when the fence is relatively soft, higher modernresponse can be excited, leading to significant increases of the variations of the tip velocity and acceleration.
Key Words
large-eddy simulation; flow-induced vibration.
Address
Fuh-Min Fang, Department of Civil Engineering, National Chung-Hsing University, 250 Kuo-Kuang Road, Taichung, Taiwan 40227, R.O.C.rnJin-Min Ueng and J. C. Chen, Department of Civil Engineering, National Chung-Hsing University, Taiwan, R.O.C.
Abstract
Wind tunnel pressure measurements and numerical simulations based on the Reynolds StressrnModel (RSM) are compared with full and model scale data in the flow area of impingement, separationrnand wake for 60 o and 90 o wind azimuth angles. The phase averaged fluctuating pressures simulated by thernRSM model are combined with modelling of the small scale, random pressure field to produce the total,rninstantaneous pressures. Time averaged, rsm and peak pressure coefficients are consequently calculated.rnThis numerical approach predicts slightly better the pressure field on the roof of the TTU (Texas TechrnUniversity) building when compared to the wind tunnel experimental results. However, it shows a deviationrnfrom both experimental data sets in the impingement and wake regions. The limitations of the RSM modelrnin resolving the intermittent flow field associated with the corner vortex formation are discussed. Also,rncorrelations between the largest roof suctions and the corner vortex
Abstract
Mean surface pressures and overall wind loads on hemispherical domes immersed in arnboundary layer were obtained by numerical simulation. The effects of alternative turbulence models,rnReynolds Number and surface roughness were examined and compared with earlier studies. Surfacernpressures on dual hemispherical domes were also calculated for three wind orientations (0 o , 45 o , and 90 o )rnto evaluate flow field interactions. Calculated values were compared to wind-tunnel measurements made inrnequivalent flow conditions.
Address
R. N. Meroney, Civil Engineering Department, Colorado State University, Fort Collins, CO 80523, USArnC. W. Letchford and P. P. Sarkar, Wind Science and Engineering Research Center, Texas Tech University, Lubbock TX 79409, USA
Abstract
This paper describes a CFD investigation into the flow over the cab of a bluff-fronted lorry.rnSeveral different simulations were undertaken, using the commercial codes: CFX, Fluent and PowerFLOW.rnUsing the k - e turbulence model, the flow over the cab was symmetric, however, using more accuraternturbulence models such as the RNG k - e model or the Reynolds Stress Model, the flow was asymmetric.rnThe paper discusses whether this phenomenon is a real effect or whether it is a solver artefact and thernstudy is supported by experimental evidence. The findings are preliminary, but suggest that it has arnphysical origin and that it may be aspect ratio-dependent.
Address
Tanya Prevezer and Jeremy Holding, Aerodynamics Team, AEA Technology Rail, rtc Business Park, London Road, Derby, DE24 8YB, UKrnAdrian Gaylard and Robert Palin, Fluids Group, MIRA, Watling Street, Nuneaton, UK
Abstract
The application of Large Eddy Simulation (LES) in a curvilinear coordinate system to thernflow around a square cylinder is presented. In order to obtain sufficient resolution near the side of therncylinder, we use an O-type grid. Even with a curvilinear coordinate system, it is difficult to avoid thernnumerical oscillation arising in high-Reynolds-number flows past a bluff body, without using an extremelyrnfine grid used. An upwind scheme has the effect of removing the numerical oscillations, but, it isrnaccompanied by numerical dissipation that is a kind of an additional sub-grid scale effect. Firstly, werninvestigate the effect of numerical dissipation on the computational results in a case where turbulentrndissipation is removed in order to clarify the differences between the effect of numerical dissipation. Next,rnthe applicability and the limitations of the present method, which combine the dynamic SGS model withrnacceptable numerical dissipation, are discussed.
Key Words
Large-eddy-simulation; square cylinder; dynamic SGS model; numerical dissipation
Address
Yoshiyuki Ono, Technical Research Institute Obayashi Corporation 4-640, Shimokiyoto, Kiyose, Tokyo 204-0011, JapanrnTetsuro Tamura, Tokyo Institute of Technology 4259, Nagatsuda, Midori-ku, Yokohama 226-8502, Japan
Abstract
Numerical flow computations around an aeroelastic 3D square cylinder immersed in thernturbulent boundary layer are shown. Present computational code can be characterized by three numericalrnaspects which are 1) the method of artificial compressibility is adopted for the incompressible flowrncomputations, 2) the domain decomposition technique is used to get better grid point distributions, and 3)rnto achieve the conservation law both in time and space when the flow is computed a with moving andrntransformed grid, the time derivatives of metrics are evaluated using the time-and-space volume. Tornprovide time-dependant inflow boundary conditions satisfying prescribed time-averaged velocity profiles, arnconvenient way for generating inflow turbulence is proposed. The square cylinder is modeled as a 4-lumped-massrnsystem and it vibrates with two-degree of freedom of heaving motion. Those blocks which surroundrnthe cylinder are deformed according to the cylinder
Key Words
aeroelastic problem; 3D square cylinder; turbulent boundary layer; computational fluid dynamics; domain decomposition technique; moving and transformed grid; generating inflow turbulence.
Address
Hiroto Kataoka, Technical Research Institute, Obayashi Corporation, 4-640 Shimokiyoto, Kiyose-shi, Tokyo 204-8558, JapanrnMinoru Mizuno, Department of Environmental Engineering, Osaka University, 2-1 Yamadaoka, Suita-shi, Osaka 565-0871, Japan