A numerical simulation study on vortex-ring collisions upon arbitrary solid boundary

• Main Author: Leong, Sheng Yuan
• Other Authors: New Tze How Daniel
• Format: Final Year Project
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/74516
• Institution: Nanyang Technological University

In this study, vortex behaviour near to complex geometry was investigated experimentally and numerically by studying the collision of a Re 2000 vortex ring upon V-shaped plates with 30, 60, 90 degrees vertices. Normal collision of vortex ring upon flat wall was also simulated using large eddy simulation (LES). The numerical results showed that LES is capable in predicting important vortex features qualitatively. The results of vortex ring colliding upon V-plates showed that the transverse ends of vortex ring, which collided earlier with the wall, induced secondary vortex and entrained it rapidly accompanied with significant reduction of core’s size. This phenomenon is similar to the lower core of vortex ring in oblique collision upon a flat wall. Other part of vortex ring collided with the wall subsequently and induced secondary vortex at different locations and times. Due to the decreasing transverse spacing in the V-shaped groove, azimuthal instabilities developed on primary and secondary vortices. The azimuthal waviness was compressed and displaced toward the longitudinal plane. It was followed by intense self-interaction and three-dimensional vortex stretching between the azimuthal waviness. The entire vortex structure was then stretched longitudinally with the production small scale hairpin vortices. It was found that the greater the vertex angle, the weaker shearing action experienced by the primary vortex. It resulted in stronger induction of boundary layer and secondary vortices which led to more intense interaction between primary and secondary vortex. However, the interaction between boundary layer and small scale hairpin vortices still remain unclear due to its complicated and three-dimensional nature. Future research can be conducted to understand more about the formation and breakdown of small scale vortices at the near-wall region.