A LABORATORY INVESTIGATION OF CHARACTERISTICS OF TORNADO-LIKE VORTICES OVER VARIOUS ROUGH SURFACES

In this paper, by using the method of experimental simulation in laboratory, the effects of three various rough surfaces on tornado-like vortices are studied in the laboratory for simulating tornado vortex at the Disaster Prevention Research Institute, Kyoto University, Japan.In the experiments, the distribution of the horizontal wind speed and direction at five different heights were measured with a heatwire anemometer and micro-wind direction indicator. The characteristics of wind speed and direction distribution for the tornado vortex on the various rough surfaces were first revealed with the simulative method of laboratory.By changing the swirl ratios(S=tanθ/2a) of simulation device, it is found that the scales of tornado-like vortex core will almost become identical, when the swirl ratio S exceeds a certain value (S>1.5).The experimental results not only explain the observed fact in the atmosphere but also provide the experimental bases for some theoretical research.