Koji Kondo

Development of a new k−ε model for flow and pressure fields around bluff body

It is well known that applications of the standard k−e model to flowfields around bluff-shaped bodies, often yield serious errors such as overestimation of turbulence kinetic energy k in the impinging region. Murakami, Mochida and Kondo have proposed a new k−e model which resolves these problems by modifying the expression for eddy viscosity approximation. This paper examines the applicability of this new k−e model (MMK model) to flowfields around three types of bluff bodies, i.e. a 2D square rib, a cube and a low-rise building model with 1 : 1 : 0.5 shape. The first half of the paper investigates the accuracy of the MMK model in reproducing turbulence characteristics around a bluff body. Results of the MMK model are compared precisely with those of the standard k−e model, a revised k−e model proposed by Launder and Kato (LK model) and wind tunnel tests for flow fields around a 2D square rib and a cube. The MMK model is also applied to predicting surface pressures on a low-rise building model with 1 : 1 : 0.5 shape with various wind angles including an oblique one. The accuracy and applicability of the MMK model to wind engineering problems are then discussed by comparing its results with those of the standard k−e model and of the wind tunnel tests.

Generation of velocity fluctuations for inflow boundary condition of LES

In this study, inflow turbulence for LES was generated by the method of Hoshiya [Proc. JSCE 204 (1972) 121–128] based on Monte Carlo simulation considering power spectral density and cross-spectral density as targets. The generated inflow turbulence was modified to satisfy the continuity equation by divergence-free operation based on the method of Shirani et al. [Report TF-15, 1981, Mechanical Engieering Department, Stanford University]. As a result, inflow turbulence satisfied the prescribed spatial correlation and power spectral density and the level of velocity divergence was sufficiently reduced. To confirm the applicability of generated inflow turbulence, it was used as the inflow boundary condition for simulating decaying isotropic turbulence with the same conditions as the experiment by G. Comte-Bellot and S. Corrsin [J. Fluid Mech. 48 (1971) 273–337]. Decay of turbulence kinematic energy in the streamwise direction was reproduced well by LES using generated inflow turbulence.

Fluctuating wind pressure measured with tubing system

Abstract Methods to measure fluctuating pressure passing through PCV tube has been developed. This research concerns with a method using PCV tube and a method averaging pressures on many points by using multi-tubes system. It was confirmed that the FFT digital filter method eliminated the distortion caused by PCV tube and that the multi-tubes system possessed the characteristic of averaging pressures on many points. The tube system was applied to field measurement of dome and wind tunnel test of rectangular prism. Useful result for pressure was obtained from the field measurement and a response analysis of building was conducted as the wind force was the averaged pressure measured with multi-tubes system.

Evaluation of effect of micro-topography on design wind velocity

Abstract Wind flow around micro-topographic features is very complicated. It includes convergent flow, separated flow and reverse flow. Since wind directions and velocities vary greatly around such features, it is very important to estimate accurately the flow fields around them. We have utilized a triple-split probe that can measure wind directions and velocities in complicated flow fields, and investigated micro-topographic effects on design wind velocity by conducting wind tunnel tests. This paper introduces micro-topographic effects, “topographic multipliers”, for several kinds of up-slope cliffs. When no flow separation is observed, for slope gradients of 7.5° and 15°, topographic multipliers for mean wind velocities take maximum values of 1.3–1.4 at x / H =0, but those for fluctuating wind velocities are small. When flow separation is observed, for slope gradients of 30°, 45° and 60°, topographic multipliers for mean components take maximum values of 1.3–1.4 at 0⩽ x / H ⩽1, and those for fluctuating components become very large in a separation bubble, and the influence of topography reaches x / H =6 and z / H =2 for each slope. No flow separation is observed for a curved surface whose mean slope gradient is 24°, and distributions of topographic multipliers resemble those for a slope gradient of 15° at x / H ⩾0. Thus, topographic multipliers for a curved surface can be predicted by its mean slope gradient.

Prediction of the wind induced response of multi-story building — Using simultaneous multi-channel measuring control system —

Abstract Progress in structural engineering has enabled higher, more complex-shaped buildings to be realized. Therefore, to ensure bot only structural reliability but also habitability of buildings, it is necessary to examine the characteristics of fluctuating wind forces acting on them. The instantaneous fluctuating wind forces acting simultaneously on many parts of a building are very useful in calculating its response by a time-dependent response analysis. Hence, a Multi-channel Measuring Control System has been developed to enable simultaneous measurement of these forces in wind tunnel tests. This paper first outlines this Multi-channel Measuring Control System. Next, it describes a wind tunnel test and a time-dependent response analysis to explain how the wind-induced response of a particular building, which possesses a coupled vibration mode, is predicted. Furthermore, it also explains the characteristics of wind forces and the response of the building. Hence, the usefulness of the system is comfirmed by showing that the response of the building with coupled vibration modes can be predicted easily. In addition, the response is used to evaluate the buildings habitability based on the Japanese guidline.

Revision of AIJ Recommendations for Wind Loads on Buildings

This paper introduces the 2004 version of the wind load provisions of the AIJ Recommendations for Loads on Buildings. One of the largest revisions is the introduction of wind directionality factor. If the building orientation is engineered, an economic design becomes possible that considers wind directionality. However, in this case, the combination of the along-wind force, crosswind force and torsional forces should be taken into account in the structural design not only for high-rise buildings but also for low- and medium-rise buildings. These are also introduced clearly in the provisions. The gust loading factor currently based on the tip displacement has been replaced by one based on the base bending moment. Other major revisions have been made on topographic effects, calculation formula for roof wind load, calculation formula for wind load on components and cladding, and aerodynamic shape factors.

FORMULA FOR ESTIMATING MAXIMUM ALONG-WIND LOAD ON A TOWER OF WIND TURBINE IN THE OPERATIONAL CONDITION

This paper describes equations for estimating maximum along-wind load on the structural design of a wind turbine tower in the operational condition. Some parameters are derived from field measurements and wind tunnel tests. Furthermore, the wind load estimation method is based on the gust effect factor method. First, the application terms and fundamental wind load estimation methods are shown. Second, the modeling of parameters of the equations is investigated. Lastly, the gust effect factors and maximum overturning moments are calculated using the suggested equations, and compared with field measurements. The estimated maximum along-wind loads agree with the field measurements, thus confirming the applicability of the equations.

Elastoplastic response of steel damper subjected to wind by the typhoon model

The object of this study is to evaluate the wind-induced fatigue damage of a steel damper installed at an H-type steel beam for earthquakes. A typhoon model is proposed to evaluate the extreme wind speed and the duration time of a strong wind. The applicability of the two methods, Methods 1 and 2, approximating the elastoplastic response is examined, by comparing the approximated response with that calculated by an exact analysis. The typhoon model simulates the observed typhoon conditions well. The wind speeds and accumulated duration times by typhoons are obtained. The difference between approximated and exact responses is small by about 20% even when the deformation of damper becomes nine times of that at the yield point. Overall, it became evident that the across wind response affects the fatigue damage more than the along-wind.