Wind turbine performance through Blade Element Theory

Experimental studies of turbine performance over realistic controlled conditions and at a scale that may be useful for modeling, validation and design are not common due to the required scale of both the turbine and the test facility. Testing wind turbines under controlled conditions allows advancement of understanding of rotor aerodynamics through the development of a documented experimental database, evaluation of existing standard predictive models and development of improved models. Wind turbine performance may be predicted analytically by the use of a simplified model outlined in well-developed rotor disc theory [1]. This model requires operating conditions and rotor geometries to estimate how the flow field is a affected by the presence of the rotor. If, during field operation, the required flow field information was determined then an estimate of turbine performance could be made using the same method as the analytical approach. Model development requires good experimental measurements with well documented, unobstructed conditions on a reasonable size turbine. The blade element momentum (BEM) method can also be used to determine the thrust and power of a wind turbine for chosen operating conditions. A typical representation of the vectors and forces on an element are shown in Figure 1 where is the rotor angular velocity, and W is the resultant relative velocity. To calculate the coefficient of power, a key measure of performance, using the BEM approach requires the operational conditions, geometry of the rotor, and the induction factors. The induction factors are a measure of the degree to which the flow is altered due to the presence of the rotor. The axial and tangential induction factors are derived in terms of the axial and tangential velocities immediately behind the rotor. The project is sponsored by NSERC .

For more details see a Recent CANWea poster