Effect of external turbulence on the short-wavelength instability of a counter-rotating vortex pair

• Main Authors: Jiratrakul Tunkeaw, Watchapon Rojanaratanangkule
• Format: Journal
• Published: 2018
• Subjects: Physics and Astronomy
• Online Access: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85049260868&origin=inward; http://cmuir.cmu.ac.th/jspui/handle/6653943832/59140
• Institution: Chiang Mai University

© 2018 Author(s). The effect of background turbulence on the evolution and instability of a counter-rotating vortex pair is investigated via the use of direct numerical simulation at a circulation Reynolds number of 2400. The ambient turbulence is modelled as decaying homogeneous isotropic turbulence with the initial levels of turbulence intensity (Tu) varied from 0.0% to 10.0%. The major effect of the external turbulence during the early-time development is that it reduces the vortex separation distance, leading to the mutual interaction of the two vortices. The onset to transition is also found to occur earlier. For a low-level turbulence intensity (Tu ≤ 6.25%), the vortex pair breaks down to turbulence due to the short-wavelength elliptic instability, whose characteristic is qualitatively similar to that in a quiescent background despite exhibiting a shorter wavelength. Increasing the turbulence intensity results in a decrease in the growth rate of the elliptic mode. The long-wavelength Crow mode dominates the breakdown process of the flow once Tu ≥ 7.5%. The Crow instability gives rise to the vortex disconnection and reconnection, resulting in the transformation of the vortex pair into a vortex ring.