| The interaction of a vortex ring impinging normally on a rigid surface is studied. The interaction initially generates a boundary layer which separates into a secondary vortex. The vortex ring (primary vortex) interacts with the secondary vortex, undergoes a rebound from the wall and in some cases a radial contraction. After the rebound, the primary ring interacts with the boundary again, producing a tertiary vortex. In addition, the secondary ring develops a bending wave through a Widnall instability. The later stages are characterized by a fully three dimensional flow.; A novel investigative approach combining experimental measurements (DPIV) and numerical simulations (DNS) is developed. A test case considering a ring of Reynolds number 1,000 is thoroughly discussed. As a comparison to the initial conditions derived from the experimental measurements, idealized (Gaussian) initial conditions are also simulated. The features of the flow, trajectories of the primary and secondary rings, and circulation and vorticity histories are quantified for this case.; To understand the nature of the development of the secondary vortex, a simplified model and scaling analysis is developed. The conclusions are that the boundary separation is dominated by the quickly developing external potential flow, and the strength of the secondary vortex is dependent in the proximity of the inviscid approach (dependent on {dollar}asb0/Rsb0{dollar}) and the Reynolds number. The experiments and simulations based on the experimental vorticity field show similar physics, but the relationships become more complicated due to the added factor of the vorticity distributions in the core.; A number of additional observations are made from the experimental measurements. First, a distortion in the shape of the primary vortex due to the strain field is observed. The distortion consists of the development of a tail structure and filamentation of the primary vortex near the head of the primary and secondary vortex dipole. Second, the tertiary vortex forms from a separated shear layer, unlike the secondary vortex which forms near the wall. Third, the velocity and vorticity fields are quantified in a plane parallel to the wall showing the bending instability in the secondary vortex (of wave number 6). Fourth, as the flow develops three-dimensionality, an illustrative case of the azimuthal vorticity field is followed. The development of three-dimensionality occurs relatively earlier for high Reynolds number flows.; During the course of the dissertation, the DPIV technique was extended. An adaptive approach, using window shifting and resizing, was implemented. This new method moves towards recovering the maximum allowable information from the images acquired. (Abstract shortened by UMI.)... |
