Investigation Of The Wind Characteristics And Its Application To The Wind Turbine Siting Over Rooftops Of Tall Buildings

With the economic and social development,the problem of energy shortage is becoming more and more prominent in the world.Meanwhile,the massive use of traditional fossil fuels,such as petroleum and coal,inevitably pollute the environment.Wind power is a green source of sustainable energy,which has the advantages of convenient utilization,exploitation and low cost.Therefore,the exploitation of wind energy over rooftops can alleciate above mentioned problems to some extent.At present,most of the researches on wind characteristics over rooftops mainly focus on a single building.Furthermore,there still lacks a systematic study of the effect of building parameters on wind characteristics over rooftops.Moreover,in literatures,there have been many numerical simulations conducted to investigate the wind characteristics over rooftops.However,for the study of wind conditions over rooftops,the results of numerical simulation are not accurate.Based on the above shortcomings,the present work attempts to identify the effects of building height ratio,width ratio and wind directions on wind characteristics above rooftops by wind tunnel testing.What's more,the wind energy distribution is assessed on the basis of these systematic experimental measurements.Hence,the suitable installation locations for roof-mounted wind turbines can be determined.The results of wind characteristics over rooftops are useful to install wind turbines mounted over roof.The variations of the wind characteristics over rooftops are analyzed by defining the normalized velocity,normalized turbulence intensity,pitch and yaw.In view of wind energy utilization efficiency and the maintenance costs of wind turbiens,the maximum normalized velocity,minimum normalized turbulence intensity and corresponding height are further researched.Additionally,under the premise that different wind angles appear with the same frequency,the wind characteristics for different wind angles are averaged.Thus,the distribution of the wind conditions without the dominant wind angle is analyzed.The result shows that for 0° and 22.5° wind angles,the small velocities and large turbulence intensities are captured.In comparison,it's observed that the lower wind velocities and higher turbulence intensities aren't captured by the measurements at 45° wind angle,especially for measuring points paralleling to incoming flow.In order to analyze the effect of building parameters on wind characteristics over rooftops,the building models with height ratio of 3,5 and 7 and width ratio of 1,2 and 3 are investigated.The result shows that the normalized wind velocities at the lower parts increase and the normalized turbulence intensities decrease with the increase of building height ratio for each wind angles.In addition,the effect of width ratio is opposite to that of the aspect ratio.In addition,the maximum normalized wind velocities,minimum normalized turbulence intensities and the corresponding height are analyzed with the different building parameters.Besides,considering that the pitch angle will have a great impact on the operation of wind turbines,the maximum pitch angle and corresponding height are analyzed.The result shows that compared to building height ratio,the maximum pitch angle is more sensitive to the width ratio.Based on the results of the wind tunnel test,this study investigates the wind energy and wind turbines distribution over rooftops.The distribution of wind energy over rooftops is more accurately evaluated by defining the wind energy amplification factor.Additionally,the effects of different areas over rooftops,building height ratio and width ratio on the wind energy distribution are analyzed.Due to the acceleration effect of wind speed over rooftops,the maximum wind energy amplification factor over rooftops can reach at 1.61 for a single building.In addition,the corresponding height ratio is only 1.02,which means that although when wind turbines are mounted close to roofs,there will be large wind energy.Based on the mean wind velocity and turbulence intensity o ver rooftops,the suitable installation locations of wind turbines are studied according to the current common specifications.The result shows that when wind angles are 0° and 22.5°,compared to leeward locations,the installation heights of HAWT at windward locations are lower.Compared to 0° and 22.5° wind angle,the lowest installation heights of HAWT under wind angle 45° were lower.When wind angle is 45°,HAWT can be placed below z/H=1.10 at all measurements points.Particularly,the HAWT at locations paralleling to incoming flow should be placed above z/H=1.02 for 45° wind angle.Besides,the results are lower than the experimental results in literature.In addition,the effects of height ratio and width ratio on lowest installation height of HAWT are examined.The lowest installation height of HAWT decrease with the increase of height ratio.In constrast to building height ratio,the lowest installation height of HAWT increases with the increase of width ratio.