Numerical tornado modeling for common interpretation of experimental simulators

Abstract

Numerical simulation of tornado-like vortices, like those produced in experimental facilities, poses many challenges. This is attributed to the complexity of vortical flow-field and the common practice of directly using the geometric dimensions and configuration of physical elements like guide vane angle, ceiling height, etc. of experimental simulators as a measure of parameters needed to characterize the generated vortices. The inherent differences in geometric dimensions and vortex generation mechanisms of the existing experimental tornado simulators makes such vortex characterization very ad-hoc in nature and hinders direct comparison and validation of results. Therefore, to facilitate a common interpretation of experimental simulators, a simplified numerical tornado model, representing the three types of existing experimental tornado simulators, is developed in this study. The three experimental simulators in consideration are VorTECH at Texas Tech University, Tornado Simulator at Iowa State University and WindEEE Dome at Western University as representatives of “Ward” type, “top-down” type and “3-D wind chamber” type designs, respectively. First, the numerically generated flow-field for each simulator obtained by modelling full experimental system is validated with experimental results. Then the simplification of these full laboratory models into a cylindrical computational domain is carried out by extracting vortex characterizing parameters strictly from the flow-field for various configurations. The dimensions and inlet boundary condition of the cylindrical model vary from one configuration to other and are dictated by vortex characterizing parameters like inflow depth, radius of updraft, swirl ratio etc. The result of this study is a simplified generic numerical tornado model that (i) can reproduce the flow-field of the original experimental systems, (ii) shows a direct dependence of the vortex flow-structure on parameters obtained from flow-field (as opposed to extracting them directly from the physical dimensions of experimental simulators).