Large-Eddy Simulation Study Of The Interaction Between The Wind-Turbine Wake And The Urban District

Urban wind power is an important direction for the development of distributed energy,it plays a significant role in promoting the construction of green and smart cities.In the urban environment,the strong interaction between small or medium-sized wind turbine and urban district will occur.On the one hand,the urban district will significantly affect the wake evolution,power generation characteristics,fatigue load of wind turbine,etc.On the other hand,the wind turbine also have an impact on the blocks environment,such as wind speed,turbulence intensity,pollutant diffusion,etc.However,peoples' understanding on the mechanism of the interaction between the wind-turbine and the urban environment is still insufficient and the related researches about the interaction are still lacking.In response to the above problems,the flow of ideal wind turbine and urban district is studied by large-eddy simulation.For simplified,this study uses the actuator disk model and equidistantly arranged cubic array to simulate the wind turbine and the urban district,respectively.The main research contents and conclusions of the paper are as follows:(1)The distribution of wind resources above the urban district is studied.Due to the crowing out effect of the building array,obvious acceleration appears and the turbulence is significantly increased above the urban district.The flow at the upstream region of the building array changes drastically and adjusts quickly,while the wind resources above the rooftop are not sensitive to the change of the position in streamwise direction and spanwise direction at the downstream region.(2)The evolution of medium-sized wind-turbine wake under the effect of urban district and the effect of wind-turbine wake on the blocks wind environment(wind speed and turbulence intensity)are revealed.It is found that due to the blocking effect of the urban district,a high-pressure zone is formed upstream,which significantly changes the trajectory of the wind-turbine wake and results in a faster wake recovery above the urban district,meanwhile,which causes the lateral expansion of the flow tube passing through the wind-turbine plane is greater than the vertical expansion.In addition,the wind-turbine wake suppresses the vertical momentum transport and thereby reduces the wind speed in the streamwise streets.At the top region of the blocks below the trajectory of the turbine wake,turbulence intensity substantially increases at the entrance region of the building array,while the overall turbulence intensity is considerably reduced at the bottom of the blocks.(3)The characteristics of power output and power fluctuations of rooftop wind turbines are explored,meanwhile,the impact of rooftop wind turbines on blocks wind environment and the impact of rooftop wind turbines on the diffusion of pollutant released at the upstream of the urban district are preliminary studied.The results show that due to the shear effect of rooftop,the power of rooftop wind turbines increases monotonically with height,while the power increment proportion relative to the only wind turbine array increases first and then decreases with height.The power fluctuations of rooftop wind turbines increase significantly,but they decrease monotonously with the hub height,meanwhile,which are even smaller than the power fluctuations of only wind turbine array at a specific height.The impacts of small rooftop wind turbines on the urban wind environment are mainly limited to the region directly behind the wind turbines and the impacts are almost negligible in the blocks under the height of building.However,the rooftop wind turbines have a greater impact on the diffusion of pollutant released higher than the height of building at the upstream of the urban district and they cause the overall concentration of pollutant significantly increases in the blocks.This paper aims to enrich the basic knowledge of urban wind power and provide a reference for the development of it,which has some practical significance and reference value for the engineering application.