Flow Control with Flexible Auxiliary Structures: A Comprehensive Review

Flexible biological features, such as bird covert feathers and fish fins, provide remarkable flow control without external energy input. Inspired by nature, flow control using flexible auxiliary structures has attracted substantial scientific interest in recent years. They modify flow fields through morphological reconfiguration and flow-induced flapping, thereby modulating energy exchange between the fluid and the structure. Recent research can be categorized into five major applications: drag reduction, vibration suppression, lift augmentation, noise mitigation, and mixing enhancement. This review synthesizes and critically evaluates existing studies on flexible auxiliary structures across these five application areas, with particular emphasis on the underlying flow-control mechanisms. It further analyses how key parameters, including bending rigidity, geometric dimensions, and installation position, influence the control performance. It also distills the primary challenges facing flexible auxiliary structures as they transition from theoretical research to practical applications and outlines prospects for their evolution towards intelligent control systems.