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How Vertical Axis Wind Turbines (VAWTs) Work
Wind in Urban Environments
Urban wind is the movement of air that varies with height from the ground, the shape of nearby buildings, the time of day and season of the year. Wind speeds are also locally influenced by topographical irregularities and other physical obstructions. The energy contained within the wind is proportional to the cube of its speed. Therefore, a slight difference in the average wind speed can significantly influence the energy output of a wind turbine.
Wind flow within urban environments is complex. The influences of surrounding buildings, trees and other obstacles significantly alter flow patterns. Increased turbulence levels yield higher fluctuations in wind speed and direction. Urban environments also offer numerous distinct benefits including local energy production, reduced capital investment in towers and transmission lines, as well as increased wind speeds over and around buildings, providing higher energy potential.
Unlike the traditional horizontal axis wind turbines (HAWT), a vertical axis wind turbine (VAWT) rotates around the shaft’s vertical axis. This configuration provides a number of important advantages for urban environments. VAWTs can capture energy regardless of the wind’s direction, thereby not requiring a yaw mechanism to turn and point the turbine blades toward the wind. VAWTs can also typically operate at lower rotational speeds, thereby reducing or eliminating turbine vibration and noise.
Numerical model of a building with wind flow normal to the building’s face.
The operating principles of a VAWT are shown in the schematic depiction below. For a rotating turbine, the blades will encounter a rotating wind velocity and an incoming wind velocity. Combining these wind velocities yields a total apparent wind at an incoming angle. An incoming flow not parallel to a blade yields high and low pressure regions on the blade, yielding overall lift and drag forces. Summing the forces over the rotation of the turbine yields an overall positive thrust that can be extracted as electrical power through the generator.
Schematic depiction of the operating principles of a VAWT.
Wind flow within urban environments is complex. The influences of surrounding buildings, trees and other obstacles significantly alter flow patterns. Increased turbulence levels yield higher fluctuations in wind speed and direction. Urban environments also offer numerous distinct benefits including local energy production, reduced capital investment in towers and transmission lines, as well as increased wind speeds over and around buildings, providing higher energy potential.
Unlike the traditional horizontal axis wind turbines (HAWT), a vertical axis wind turbine (VAWT) rotates around the shaft’s vertical axis. This configuration provides a number of important advantages for urban environments. VAWTs can capture energy regardless of the wind’s direction, thereby not requiring a yaw mechanism to turn and point the turbine blades toward the wind. VAWTs can also typically operate at lower rotational speeds, thereby reducing or eliminating turbine vibration and noise.
Numerical model of a building with wind flow normal to the building’s face.
How VAWTs Operate
The operating principles of a VAWT are shown in the schematic depiction below. For a rotating turbine, the blades will encounter a rotating wind velocity and an incoming wind velocity. Combining these wind velocities yields a total apparent wind at an incoming angle. An incoming flow not parallel to a blade yields high and low pressure regions on the blade, yielding overall lift and drag forces. Summing the forces over the rotation of the turbine yields an overall positive thrust that can be extracted as electrical power through the generator.
Schematic depiction of the operating principles of a VAWT.