||LARGE EDDY SIMULATION OF THE GUST INDEX OVER A REALISTIC URBAN AREA
LARGE EDDY SIMULATION OF THE GUST INDEX OVER A REALISTIC URBAN AREA
ヌルルフダ, アハマドAhmad, Nurul Huda
The aim of this research is to quantitatively present a general relationship between the intensity of gust and the urban morphology. Two large eddy simulation (LES) models named as the parallelized LES model (PALM) and lattice Boltzmann model (LBM) were executed. It was confirmed that both models produce the same accuracy. The PALM was used to validate the new gust parameter while the LBM was applied to simulate and examine the gusts environment without uncertainties in the inflow condition. The coastal area of Tokyo was selected to represent the urban morphology. The simulations run over realistic geometry surfaces of the build up area with 2 m resolution in all direction to explicitly resolve the fine building shape and also the flow at the pedestrian level. It considers only the shear driven turbulence (i.e. no Coriolis force and thermal stratification) and developed the boundary layer naturally. A new parameter called the gust index (GI) was defined as the local maximum wind speed divided by the free stream velocity. This universalize definition make it comparable quantitatively at different locations within urban canopies. Moreover, this parameter is decomposed into mean wind ratio (MWR) and turbulent part ratio (TPR) component to evaluate the quality of gustiness. This procedure can mask detailed structures of individual buildings with keeping the bulk characteristics of the urban morphology. At the pedestrian level, it is quantitatively shown that the GI decrease with increasing building coverage, λ_p, which notably contribute by the TPR through out the range of λ_p compared to the MWR. Such a result was explained by the change of flow regimes within the building canyon. Apparently, at the higher elevation above the canopy layer, the effect of the building coverage becomes irrelevant to all normalized velocity ratios and the roughness length, as a comprehensive aerodynamic property of roughness was well represented.
http://t2r2.star.titech.ac.jp/rrws/file/CTT100701742/ATD100000413/thesis_13D18070_Nurul Huda Binti Ahmad.pdf