LES study on aerodynamics of auto-rotating square flat plate by IBM and SAMR

Abstract

Windborne debris is caused by severe wind events, such as typhoons and tornadoes. Among the various shapes, sheet-shaped debris has especially complex flight behavior due to the Magnus effect induced by autorotation. In this study, we simulate flows past an autorotating flat square plate pinned with a freely rotatable axis (one degree-of-freedom) and a free-flight flat square plate (six degrees-of-freedom). Therefore, the coupled model for fluid flow and a rigid body based on large-eddy simulation has been developed using the immersed-boundary method and block-structured adaptive mesh refinement to capture details of the vortex structures around the moving plate. This model has such efficiency of computation that the boundary of the moving plate can be treated as passing through a fixed mesh pattern represented by sufficiently fine Cartesian grids, avoiding time-dependent grid generation in a boundary-fitted manner. The aerodynamics of the auto-rotating flat plate was examined and confirmed to validate the present model. Moreover, the unsteady forces based on wake vortices in the process of successive deformation are identified, and their roles on autorotation are clarified. In the case of free flight, the sensitive instability of the axis during autorotation and the effects of translational motion on rotational motion are discussed.