Effect of Angle of Attack and Blade Tip Vortex on the Noise Level of Tandem Wind Rotors of an Intelligent Wind Power Unit

The authors have invented a superior wind power unit, which is composed of tandem wind rotors and double rotational armature type generator without the traditional stator. This unit is called ＂intelligent wind power unit＂. At upwind type unit, the large-sized front wind rotor and the small-sized rear wind rotor drive the inner and the outer rotational armatures respectively, in keeping the rotational torque counter-balance between both wind rotors/armatures. This paper discusses the acoustic noise emitted from the tandem wind rotors. As for tandem wind rotors, the tip vortex shedding from the front wind rotor may make a loud acoustic noise if the vortex attacks the rear wind rotor. Intelligent wind power unit, however, has no chance to increase the acoustic noise level by the tip vortex because the diameter of the front wind rotor is reasonably larger than the diameter of the rear wind rotor. The vorticity generated in the boundary layer on the blade can be observed obviously at wake flow and can be evaluated quantitatively at flow conditions measured by a hot-wire anemometer at a wind tunnel. The flow conditions have shown that the radial and axial components of vorticities contribute to emit the acoustic noise.