A study of the effects of initial circulation upon elliptic vortex-ring behavior

• Main Author: Pu, Wen Wei
• Other Authors: New Tze How, Daniel
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Aeronautical engineering::Aerodynamics
• Online Access: https://hdl.handle.net/10356/150704
• Institution: Nanyang Technological University

Visualization and analysis of Particle Image Velocimetry measurement data sets were carried out to inspect the vortex dynamic of vortex-ring produced by (a) nozzle’s aspect ratio=1, 2, 3, 4 (b) Reynolds number=500, 1000, 2000, 4000 and (c) stroke-ratio =1.5, 3.0. Vorticity maps, vortex core trajectory and associated phenomenon, particularly axis-switching rate was examined in the study to establish the effects of different initial circulation conditions upon vortex behaviours such as fluid entrainment to enhance jet mixing. The results show that the axis-switching rate rises to a critical aspect ratio of AR=2 and drops subsequently. The increase in Reynolds number imposes less distinct but positive influence on axis-switching rate while lower stroke-ratio increases the total number of axis-switching due to its stable trajectory. Besides, the formation of trailing jet discovered at L/d=3.0 with elliptic nozzle indicates that aspect ratio affects formation number. Vortex reconnection is only observed at a high aspect ratio and Reynolds number tells that both initial conditions are essential in controlling vortex deformation. Other observations such as the formation of secondary vortices, leapfrogging, vortex stretching and bifurcation are found to be in good agreement with the past studies.