Two-dimensional vortices in strain and shear flows

+147hlm.;24c

Dynamic measurements on an airfoil using acoustic forcing

Abstract only

Dynamic measurements on an airfoil using acoustic forcing

Abstract only

Asymmetric vortex merger: mechanism and criterion

The merging of two unequal co-rotating vortices in a viscous fluid is investigated. Two-dimensional numerical simulations of initially equal sized Lamb-Oseen vortices with differing relative strengths are performed. Results show how the disparity in deformation rates between the vortices alters the interaction. Key physical mechanisms associated with vortex merging are identified. A merging criterion is formulated in terms of the relative timing of core detrainment and destruction. A critical strain parameter is defined to characterize the establishment of core detrainment. This parameter is shown to be directly related to the critical aspect ratio in the case of symmetric merger

Two-Dimensional Vortices in Strain and Shear Flows

+147hlm.;24c

Decay of monopolar vortices in a stratified fluid

The decay of monopolar vortices in a stratified fluid has been investigated experimentally, and the observations have been compared with an analytical decay model that accounts for both the increasing vertical thickness and the radial expansion of these pancake-like structures. The monopolar vortices were generated by two different forcing techniques, and the corresponding horizontal velocity field was measured by tracking passive tracer particles. It was found that the monopolar vortices are characterized by a core of single-signed vorticity and a ring of oppositely signed vorticity, and that their net circulation is zero. The observations are in good agreement with the theoretical model, which provides a better description of the vortex evolution than the diffusion models presented in earlier studies

Decay of monopolar vortices in a stratified fluid

The decay of monopolar vortices in a stratified fluid has been investigated experimentally, and the observations have been compared with an analytical decay model that accounts for both the increasing vertical thickness and the radial expansion of these pancake-like structures. The monopolar vortices were generated by two different forcing techniques, and the corresponding horizontal velocity field was measured by tracking passive tracer particles. It was found that the monopolar vortices are characterized by a core of single-signed vorticity and a ring of oppositely signed vorticity, and that their net circulation is zero. The observations are in good agreement with the theoretical model, which provides a better description of the vortex evolution than the diffusion models presented in earlier studies

Kinematic properties of monopolar vortices in a strain flow

The advection properties of monopolar vortices subjected to background strain were investigated both experimentally and numerically. Dye-visualization studies in a stratified fluid demonstrated the deformation of the vortex core and the shedding of passive tracers from the edge of the vortex. The main kinematic characteristics of the vortex evolution could be well captured by a simple model, in which the monopole was represented by a (strength-varying) point vortex surrounded by a contour of passive tracers. Full numerical simulations of the vortex evolution showed an excellent agreement with the observed tracer distributions and also revealed that the spatial distribution of vorticity must be taken into account in order to explain the final tearing of the laboratory vortex