Interaction of vortex ring with perforated plate at different included angles

Abstract: Experiments are performed to investigate the interaction of a vortex ring (Reynolds number based on circulation (Re_Gamma = 10500) with perforated surface (open area ratio, phi_1 = 0.24 and phi_2 = 0.44) with different included angles (theta = 60deg-180deg). The phenomenon is characterized using techniques like planer laser-induced fluorescence (PLIF) imaging and particle image velocimetry (PIV). Lagrangian analysis using finite-time Lyapunov exponents (FTLE) and Gamma_2 vortex identification methods are utilized to understand flow physics. We observe the development of mushroom-like structures at the holes, driven by the induced flow of the vortex ring. These formations, together with Kelvin-Helmholtz instability, introduce initial instability to the emerging jets. We discern a sequential emergence of the vortex ring in the form of jets at lower theta value that diminishes at higher values. Notably, a single vortex ring is split into two distinct vortex rings for theta less than equal to 120deg. On either side of the perforated plate, the sense of circulation after interaction does not show bias towards the sense of flow on the upstream region for some values of theta. We further show the evolution of circulation by jets in the downstream region aligns with the proposed cumulative slug flow model using the centre line peak velocity of individual jets.