Abstract:In order to study the effect of the hill slope on the wind field characteristics of hilly terrain, the spatial averaged large eddy simulation (LES) method was adopted to simulate the unsteady flow around the hilly terrain. The simulation method and parameter settings were firstly verified by comparison with the wind tunnel experimental results. The influence of four slopes, i.e., 15°, 21.8°, 30° and 45 °, on the wind field and turbulence structure of hilly terrain was then analyzed in the aspect of the time averaged and the transient flow field. Finally, by comparing with different national specifications, the influence of hill slope on the terrain acceleration effect was analyzed. The results show that LES method can simulate the characteristics of mean wind and fluctuating wind of hills with different slopes. With the considered four slopes of the hill, the mean wind and fluctuating wind fields on the windward side of hills with different slopes are basically the same, and the differences are mainly at the top and leeward side. At the top of the hill, with the slope increases, the turbulence at the top of the hill increases, the mean flow velocity decreases with there exists a critical slope of 30°. The flow separation point gradually moves downstream, causing the location of the vortex core center to move downstream and away from the mountain wall. Around the near wall region of the hillside of the leeward surface of the hill, there exists a critical slope of 30°. When the slope is smaller, the vortex scale increases with the slope angle; meanwhile, the vortex shedding path gets wider and energy concentration. Moreover, the mean flow wind decreases and the turbulence intensity increases. However, when the slope is greater than the critical value, reverse trend occurs. The acceleration effects of different slopes are similar, and the main difference lies in the near wall region. With the increase of the slope, the acceleration effect of the windward surface,the top of the hill and leeward surface increase after first decreases. The maximum value is given in combination with national specification for reference.