Abstract
The study involved determining the performance of a Magnus-type Vertical Axis Wind Turbine (VAWT) subjected to typhoon wind speeds. The investigation is purely numerical, starting with the validation of the Magnus effect on lift and drag generation of a rotating cylinder in similar flow conditions as the wind turbine experiences. Validation data was culled from a related experimental study on Flettner rotors as used in ship propulsion augmentation applications. The validated aerodynamic performance of the cylinders is assumed to be sufficient to model the wind turbine performance. The scale of the 2-cylinder model rotor is equal to the actual Magnus VAWT of Challenergy Inc. The published rated capacity of the Magnus VAWT is 10 kW while the simulated rotor running at the same rated conditions produced 9.42 kW at a Tip Speed Ratio (TSR) of 1.17 resulting in a Power Coefficient (CP) equal to 0.5. Simulating the rotor at a wider range of TSRs reveals a peak performance point of CP = 0.58 at a tip speed ratio of 2. This does not take into account the input power consumed by rotating the cylinders and hence is expected to be significantly lower in the actual conditions. A 2-dimensional model of a 2-cylinder Magnus-type rotor was created with a cylindrical blade diameter of 1 m and a rotor radius of 3 m. Rated conditions are at 8 m/s wind speed with a rotor rotational speed of 30 rpm and cylinder rotational speed of 150 rpm. Experimental validation data was adopted from a wind tunnel test of a Flettner rotor under flow conditions of Reynolds number equal to 1 × 106. Lift and drag curves were compared between simulation and experiments, revealing an excellent agreement in lift while a significant disagreement in drag. Simulations underpredict the drag, which resulted in the unusually high predicted performance of the wind turbine. The VAWT performance agreed well with the published rated capacity of 10 kW with a predicted power output of 9.42 kW. A tip speed ratio sweep was conducted and revealed a peak performance point at TSR = 2 with CP equal to 0.58, subsequently dropping to CP = 0.35 at TSR = 5. When the rotor was simulated at typhoon wind speeds, the results showed increasing power outputs from 30.87 kW at 13.89 m/s, 99.67 kW at 20.83 m/s, 140.38 kW at 28.61 m/s, up to 176.79 kW at a cut-out wind speed of 40 m/s. The corresponding CPs are observed to decrease as wind speeds increase from 0.5, 0.31, 0.30, 0.16 down to 0.8.
