Vortex Dynamics Arising from Successive Vortex Rings Impacting Concave Asymmetric Cavities

Tracheoesophageal (TES) speech is one of the most popular artificial voice rehabilitation techniques. During the production of TES, air passes through the tracheoesophageal prosthesis and enters the esophagus, generating successive vortex rings that impinge on the concave esophageal wall. A fundamental understanding of this fluid-structure interactions would help improve the success rate of TES, which is currently only 65%. This fundamental fluid-structure interaction also has applications to areas such as heat transfer enhancement and targeted fresh air supply. This study investigated the physics of successive vortex ring interactions with an asymmetric (hemicylindrical) concave cavity. Two successive vortex rings, referred to as leading and trailing, were generated with formation number of and Reynolds Number of using a piston-cylinder vortex ring generator inside a water tank. The frequency of the vortex ring generation was matched with that of TES. Three different ratios of vortex ring radius, R_v, to hemicylindrical cavity radius, R_cyl, were examined; namely, γ = R_v/R_cyl = 1/3, 1/2, and 2/3. Flow visualization and particle image velocimetry techniques were employed to quantify the interactions. Upon impact of the leading vortex ring on the cavity surface, secondary vorticity is generated. However, when the successive trailing vortex impacts the cavity wall, no secondary vorticity is generated despite the trailing vortex producing stronger wall-bounded vortices due to the vorticity sheet from the leading vortex ring. Aerodynamic loading on the structure is also estimated and discussed.