Free fall of perforated thick plates

Adding a central hole to freely falling thin plates (hl≪10−2) has been shown to enhance stability and produce falling motions such as helical precession and Hula-Hoop motions, but the effects of such perforations on thick plates remain largely unexplored. This study numerically investigates the free fall of thick perforated plates (hl∼10−1) across a Reynolds number range of 103≤Re≤105 using Immersed Boundary-Lattice Boltzmann Flux Solver. In addition to flutter and tumble found in solid plates, three new falling trajectories are identified: “S-curve,” “Glide,” and “Vertical fall.” The S-curve exhibits high-frequency oscillations modulated by a low-frequency envelope, producing a macroscopic periodic trend. Glide and Vertical fall are stabilized by high-frequency alternating torques, resulting in minimal macroscopic rotation. A progression in motion stability is observed from S-curve to Vertical fall and ultimately to Glide mode. Analysis reveals that geometric modifications and vortex dynamics play a dominant role in the formation of these modes. Increasing the central hole size promotes the onset of the more stable Glide regime, consistent with observations from previous studies on thin plates. However, unlike thin plates, where greater thickness improves stability, thick plates become less stable as thickness increases.