Numerical Implications of Solidity and Blade Number on Rotor Performance of Horizontal-Axis Wind Turbines

Abstract

A numerical study was conducted to examine the impact of rotor solidity and blade number on the aerodynamic performance of small wind turbines. Blade element momentum theory and lifting line based wake theory were utilized to parametrically assess the effects of blade number and solidity on rotor performance. Increasing the solidity beyond what is traditionally used for electric generating wind turbines led to increased power coefficients at lower tip speed ratios, with an optimum between 3 and 4. An increase in the blade number at a given solidity also increased the maximum C p for all cases examined. The possibility of a higher aerodynamic power extraction from solidity or blade number increases could lead to a higher overall system power production. Additional advantages over current 5% to 7% solidity, high speed designs would include lower noise, lower cut-in wind speed, and less blade erosion.

Small-scale wind energy portable turbine (SWEPT)

“…The conventional LSWT has solidity in the range of 5%-7%. However, for the SSWTs, solidity may be as high as 50%, depending upon the size of wind turbine [22,35]. The solidity of SWEPT was equal to 30% which is in agreement with the literature.…”

“…However, for the SSWTs, much higher solidity has been reported at the maximum power coefficient. The optimal solidity in the range of 15%-25% has been suggested by Duquette and Visser [22] for the wind turbine of 2 m diameter. This figure increased up to 50% as the diameter decreased to ~23.5 cm [35].…”

“…Each of these components should be designed, optimized and mutually synchronized in such a fashion that they operate at their rated operating condition. There are very few attempts available in literature that study the conducted by Duquette and Visser [22] to assess the effects of blade number and solidity on the performance of 2 m diameter wind turbine. The study suggested that by increasing the solidity from the conventional range of 5%-7% to 15%-25% one can achieve better power coefficient values.…”

“…Solidity of a wind turbine is defined as the ratio of surface area of the blades to its total swept area and is given by expression [22] :…”

“…Further, it does not consider any type of losses that reduce the torque and power of the wind turbine. Out of many mathematical models, Prandtl method is the most frequently used, which expresses tip and hub loss factors as [22]:…”