Power production locality of bluff body flutter mills using fully coupled 2D direct numerical simulation

Two-dimensional fully coupled direct numerical simulations (DNS) are conducted to examine the local energy dynamics of a flexible cantilever plate in the wake of a two-dimensional circular cylinder. The motion of the cantilever plate is described using a finite element formulation and a fully compressible, finite volume Navier Stokes solver is used to compute the flow field. A sharp interface level set method is employed in conjunction with a ghost fluid method to describe the immersed boundaries of the bluff body and flexible plate. DNS is first conducted to validate the numerical methodology. The results are compared with previous studies of flexible cantilever plates and flow over bluff bodies showing excellent agreement. A newly defined power production / loss geometry metric is introduced based on surface curvature and plate velocity. The metric is found to be useful for determining which sections of the plate will produce energy based on curvature and deflection rate. Scatter plots and probability measures are presented showing a high correlation between the direction of energy transfer (i.e., to or from the plate) and the sign of the newly defined curvature-deflection-rate metric. The findings from this study suggest that a simple local geometry/kinematic based metric can be devised to aid in the development and design of flexible wind energy harvesting flutter mills.