Experimental investigation on the influence of swirl ratio on tornado-like flow fields by varying updraft radius and inflow angle

Abstract

Abstract The swirl ratio is recognized as the most critical parameter for determining the tornado-like vortex. Many laboratory simulators have studied the effect of swirl ratio by changing the angle of entry flow, but there is a lack of research on the updraft radius. Therefore, a laboratory tornado simulator was designed, constructed and tested to generate tornado-like vortices. Different from the existing tornado simulator, this simulator allows to change the updraft radius. And, the effects of various swirl ratio caused by the updraft radius and the angle of entry flow on the tornado-like vortices were investigated, in terms of the dual-celled vortex transformation and vortex wandering. It was found the effects of the updraft radius and the angle of turning vanes on the tornado-like vortices are quite different, and the formation of dual-celled vortex are more sensitive to the updraft radius, because a larger angular momentum and axial pressure gradient can be provided. In addition, increasing the updraft radius has a greater inhibitory effect on the vortex wandering phenomenon compared to the angle of the turning vanes due to the flow fluctuations induced by turbulence.