Vortex Ring Interactions with Hemicylindrical Cavities

Tracheoesophageal (TE) speech is the technique of restoring voice to a patient following a laryngectomy. During TE speech the flow is characterized by periodic vortex rings impinging on the posterior wall of the trachea. That is, the fundamental interaction is characterized by a vortex ring impinging on a hemicylindrical cavity. This scenario is relevant to a number of fundamental fluid mechanics problems. The objective of this work is to experimentally identify, for the first time, the primary physics of a vortex ring impinging on hemicylindrical cavities of varying radius. A piston-cylinder vortex generator in a water tank was used to create a vortex ring with a formation number of F = 2.67 and Reynolds number of Re_Γ = 1450. Five different ratios of vortex ring radius (R_v ) to hemicylindrical cavity radius (R_cyl ) were examined, namely, γ = 1/4, 1/3, 2/5, 2/3. Planer laser induced florescence (PLIF) and color dye flow visualization technique were employed to visualize the primary interactions. Flow visualization data qualitatively reveal how surface curvature of the hemicylindrical cavities affects the radial spreading of the primary vortex ring, and the subsequent inducement and separation of wall-bounded vorticity. Comparison with the physics arising due to vortex ring impingement on axisymmetric concave cavities (i.e., hemispheres) is also established in this study.