Abstract
We carried out a wind tunnel experiment to examine the power generation efficiency of a stand-alone miniature wind turbine and its wake characteristics at different tip speed ratios (TSRs) under the same mean inflow velocity. Resistors in the electrical circuit were adjusted to control the TSRs to 0.9, 1.5, 3.0, 4.1, 5.2, and 5.9. The currents were measured to estimate the turbine power outputs versus the TSRs and then establish the actual power generation coefficient Cp distribution. To calculate the mechanical power coefficient, a new estimation method of the mechanical torque constant is proposed. A reverse calibration on the blade rotation speed was performed with given electrical voltages and currents that are used to estimate the mechanical power coefficient Cp, mech. In the experiment, the maximum Cp,mech was approximately 0.358 (corresponding to the maximum Cp of 0.212) at the TSR of 4.1. Significant findings indicate that the turbine at the TSR of 5.2 produces a smaller torque but a larger power output compared with that at the TSR of 3.0. This comparison further displays that the turbine at the TSR of 5.2, even with larger power output, still produces a turbine wake that has smaller velocity deficits and smaller turbulence intensity than that at the TSR of 3.0. This behavior demonstrates the significance of the blade-rotation control (i.e., pitch regulation) system to the turbine operation in a large wind farm for raising the overall farm power productivity.
Highlights
In recent years, green energy has gradually gained attention due to raising awareness of environmental protection
Some studies present that the shaft torque as a function of the blade angular velocity has a similar parabolic distribution with the maximum at a blade angular velocity. These results indicate that the initial increase of the blade rotation speed can raise the blade generating shaft torque and the power generation efficiency, but too high blade rotation speeds lead to a reduction in the torque and power generation efficiency
The resistor could be adjusted to achieve the turbine blade rotating at the different angular velocities under the same hub-level incoming velocity
Summary
Green energy has gradually gained attention due to raising awareness of environmental protection. A previous study by Dilip and Porte-Agel [21] showed that pitch regulation, which is applied to adjust the blade angular velocity of the upstream turbines with a decreased pitch angle of −2 degrees (i.e., changes the original TSR of the rotor) in the in-line two-turbine simulations, can mitigate the wake effects on the downstream turbines and increases the total power output by 2.8% at a lower inflow turbulence condition. Such a strategy can be viewed as an alternative to increasing the power produced in a massive wind farm operation in the future.
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