Assessment And Optimization Of Pedestrian-Level Wind Environment For Tall Buildings In Urban Area

With the development of China's economy,the proportion of urbanization has witnessed the rapid increase.Accordingly,the urban space has become increasingly high-density.Meanwhile,various high-rise buildings of different shapes have also been widely built-up.However,the presence of high-rise buildings can significantly influence the air ventilation in urban areas,resulting in obvious high wind speed areas around the buildings,which in turn deteriorate pedestrian comfort,and even threaten the pedestrian safety.This issue is often referred to as“pedestrian-level wind environment?PLW?”.And this paper mainly focueses on the pedestrian-level wind environment of tall buildings in urban areas.Therefore,the main content of this study are as follows:?1?Five different SRANS turbulence models and two differnet inflow turbulence generation are used for the validations of CFD simulations of wind environment around a standalone square tall building.The results show that the RNG k-?model is the most accurate and provided the smallest discrepancies amomg all the five SRANS model.For LES,the DSRFG method performs better and the LES model with DSRFG method is significantly better than RANS model,particularly in the low wind speed region,but its computational efficiency is much lower than SRANS model;?2?Based on wind tunnel test and CFD numerical simulations,this paper investigates the PLW of five different building shapes and four different layouts for groups of high-rise buildings.The results show that CFD numerical simulations based on SRANS method can obtain the consistent results with the wind tunnel test in the high wind speed region,but obvious discrepancies observed in the low wind speed region;The most unfavorable wind direction angles of square,H-shaped and X-shaped buildings are located in the oblique wind directtion,while the cross and Y-shaped are located in the normal wind direction;Considering the influence of building layouts and shapes,the wind environment of Y-shaped in the staggered layout is the best,the worst wind environment is the H-shaped in the enclosed layout;?3?Based on the wind climate data of Beijing and Hong Kong,the influence of actual wind climate on PLW is further studied.Under different wind climates,the optimal building layout is staggered.And in the Beijing wind climate,the wind environment of Y-shaped and staggered layout is the best;but the best wind environment under Hong Kong wind climate is the square and staggered layout;?4?Among four different specifications for PLW,the difference between the most relaxed?Melbourne standard?and the most stringent?Isyumov&Davenport criteria?is53.80%for sitting a long time;the difference between the most relaxed?Melbourne standard?and the most stringent?Isyumov&Davenport?reached 36.60%for a short time;the difference between the most lenient?Melbourne standard?and the most stringent?NEN8100 specification?reached 19.73%for strolling;?5?Four different parameters were used to optimize the pedestrian-level wind environment of group of tall buildings based on NEN8100,the results show that the optimal PLW environment can be obtained when the most favoured wind direction of groups of tall buildings coincides with the meteorological wind direction with the maximum value of A?1×U_mp?wind direction frequency and most probable wind speed?;?6?Using CFD numerical simulations,the PLW environment of the second tallest building in China was evaluated and optimized by the optimization framework prposed in this study.The results show that the most favorable wind direction of the super-tall building is 67.5°,and the most unfavorable wind direction is 270°;for sitting a long time,26.01%of the urban area meet the comfort requirements before optimization,which was increased up to 43.46%after optimization;for sitting for a short time,45.24%of the urban area satisfy the comfort requirements,while was also improved to 63.00%before optimization;for strolling,90.22%of the urban area considered was slightly increased to95.36%after optimization,.