Collision of elliptic vortex-rings upon flat-walls

• Main Author: Er, Pei Song
• Other Authors: New Tze How, Daniel
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Aeronautical engineering::Jet propulsion
• Online Access: https://hdl.handle.net/10356/154557
• Institution: Nanyang Technological University

In this report, elliptic vortex-ring of AR = 4 were numerically simulated with Ansys Fluent using the LES to capture the structure of the larger eddies, and the WALE model is used as more emphasis is preferred when simulating the flow behaviour as it collides with the flat surfaces. This project aims to investigate and analyse the secondary and tertiary vortex structures produced as an elliptic vortex-ring collides with: (a) Flat wall, (b) 30 ° inclined slope, and (c) 60° inclined slope. Free elliptic vortex-rings are first generated for both coarse and fine mesh cases to determine the periodic location upon which axis-switching behaviour of the vortex takes place. Subsequently, for the coarse mesh study, a flat wall is put in place at the locations where the 1st and 2nd cycle of axis-switching is completed. Similarly, one 30° and one 60° inclined slopes of different orientation was then placed such that the vortex will interact with the surfaces as it is completing its 1st cycle of axis-switching. For the fine mesh study, there is only 1 fixed orientation of the individual inclined slopes being numerically simulated along with a flat wall. Results show that for the flat wall, unlike the behaviour exhibited by circular vortex-rings, the cores of the elliptic vortex-rings tend to propagate along the surface in the minor axis direction, greatly increasing the core-to-core diameter of the vortex. This motion tends to shear the core of the vortex, flattening them along the surface and subsequently only secondary vortices are formed before the primary cores breaks down. For the 60° inclined slope, flow behaviour of the elliptic vortex rings largely homogenous to that of the circular vortex-ring, with partial entrainment of the core closer to the surface by the other core occurring. In the case of the 30° inclined slope, a large portion of the core closer to the surface gets entrained by the other core, causing it to split into 2 and lead to rapid decay of the vortex.