Effect of radial inflow on vortex intensification and its application to wind vortex generators
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A new wind vortex turbine, called "tornado-type wind generator system," was studied both theoretically and experimentally for the purpose of better understanding the basic nature of a vortex flow and further improvement of its power efficiencies. Analytical solutions were obtained from the Navier-Stokes equations for the velocity distributions along the radial distance. The result demonstrates the important nature of a vortex structure that, in order to intensify a vortex inside the tower, radial inflow must be provided from the side walls. Based upon this concept, the essential contribution of our experimental work was to furnish the radial inflow by utilizing the dynamic head of incoming wind;One circular model of 0.36 m(14") diameter with 0.58 m(23") height and two spiral models of 0.36 m inner diameter with 0.36 m height and 0.48 m(19") inner diameter with 0.58 m height were tested in a newly constructed wind tunnel of 1.22 x 1.22 m(4' x 4') at wind speeds from 2.54 m/s (5.68 mph) to 6.1 m/s(13.65 mph). It was found that for intensifying a vortex in such a tower it is more important to require the radial inflow in the boundary layer region rather than across the entire height of the tower. The maximum power efficiency, C(,p), obtained for the circular model with the radial inflow supply was about 3.8, which is about one order higher than that of conventional wind mills. This C(,p) was increased more than 100% in some cases as compared to that without the radial inflow supply. The maximum C(,p) for the large spiral model with the radial inflow supply was the highest, a value of 9, which is 22.5 times that of conventional windmills. This C(,p) was increased only about 15-30% as compared to that without the radial inflow supply because the spiral model produces the radial inflow by itself due to the decreasing radius of the spiral curvature. Static pressure measurements in the vortex core of the large spiral model showed that the maximum static pressure drop at the vortex center was more than 10 times the dynamic head of the wind with the radial inflow supply. The radial inflow lowered the pressure in the vortex core, a consequence of vortex intensification;In conclusion, extracting wind energy by creating and maintaining an extremely low pressure region of an intensified vortex at the turbine exit through viscous pumping is an improvement for wind machines in the aspect of C(,p) and consequently is a cost effective procedure.