Recently, energy-efficient technologies are employed to buildings in terms of reduction of environmental burdens. Vertical fins on walls of tall building are environmentally-friendly components as sunshade louver. As these components are exposed to outer air, wind loads should be evaluated for wind resistant design of cladding. However, the fluctuating wind pressures or forces acting on vertical fins are generally difficult to predict with accuracy because of the reproducibility in wind tunnel experiments which require geometrically-accurate models and installations of measurement system. On the other hand, recent development of techniques on computational fluid dynamics (CFD) has enabled us to simulate the complicated flow such as the wind around buildings. Large Eddy Simulation (LES) is expected to be adopted as an effective tool to evaluate wind load for wind-resistant design of buildings. As numerical computations can overcome the difficulties of experimental prediction for complicated models of cladding and components, wind loads of vertical fins are thought to be evaluated accurately by LES. For numerical prediction of pressure fields around vertical fins by LES, unstructured grid systems are effective in terms of flexibility in generating the computational model. Present authors previously discussed the applicability of unstructured LES for prediction of the fluctuating wind pressures on building models (isolated square cylinder, two square cylinders and actual building model in a real urban district) by comparison with experiments. In this paper, the fluctuating wind forces acting on the vertical fins on walls of tall building are examined using unstructured LES. Especially, focusing on the size effects of fins, the pressure fluctuations and the flow fields are studied to evaluate wind loads for practical wind resistant design. First, the applicability of unstructured LES for wind force estimation of fins is validated by comparison with wind tunnel experiments. Here, the computation is carried out using the same geometry as the experimental model which has relatively larger fins than actual situation. Strong wind forces act on the fins placed at the corners of building and the computed force distributions coincide with experiments with accuracy. Next, the wind forces acting on the downscaled fins are computed to simulate the real situation. The flow fields and the wind force fluctuations are quite different from those of experimental (large-scaled fin) model. For the case of downscaled fins, the pressure fields around fins are dominantly influenced by the turbulence structures formed by the building scale. The scale effects on the wind load evaluation of cladding components, which can be examined by only numerical simulations, is clarified. Moreover, some cases for practical investigation are also computed (corner geometry and wind direction). As the overall trend, the maximum forces of fins at lower height become larger than other heights. In order to elucidate these phenomena, flow fields at the upwind region are visualized. The vertical flow promoted by the configuration of fins intensifies the horseshoe vortex in upwind region and the secondary vortex appears near the upwind wall on the ground level. As a conclusion of this study, for evaluation of design wind load of cladding components such as vertical fins, the scale effects should be considered for accurate prediction of pressure fluctuation. Unstructured LES is available to evaluate the wind loads of vertical fins on walls of buildings and effective to elucidate the flow mechanism on the complicated surfaces of buildings.
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Jan 18, 2023
Wentong Zhang + 3
Open Access