On the use of metasurface for Vortex-Induced vibration suppression or energy harvesting

This paper explores the use of metasurface in designing an aerodynamic system for potential vortex-induced vibration (VIV) suppression or energy harvesting. Four kinds of metasurface patterns are designed to decorate an ordinary cylinder bluff body for modifying its aerodynamic characteristics. A theoretical model is developed for the VIV system by describing the wake as a van der Pol oscillator. The aerodynamic parameters, i.e., the lift and drag coefficients, used in the theoretical model, are determined from three-dimensional CFD simulations. A wind tunnel experiment is conducted to validate the theoretical model and investigate the aerodynamic behaviors of the VIV systems with different bluff bodies. It is found that the metasurface pattern has a significant influence on the aerodynamic characteristics of the bluff body. Using different metasurface patterns to decorate the bluff body, the vortex-induced vibration of the system could be either enhanced or suppressed, compared with the baseline reference using an ordinary bluff body with a smooth surface. Furthermore, the vortex shedding processes are simulated to give further insights into the wake oscillating motions. The roles of the metasurface in suppressing or enhancing the vortex-induced vibration are reasonably explained: the existence of metasurfaces could alter the flow field around the bluff bodies and consequently the aerodynamic force. In addition, based on the validated theoretical model, it is learned from a parametric study that the power output reaches saturation when the electromechanical coupling strength is increased to a certain level. Therefore, piezoelectric transducers with moderate coupling coefficients are recommended for practical applications from the cost-effective perspective.