Turbulent energy cascade associated with viscous reconnection of two vortex rings

Dr Nguyen Van Luc (Ton Duc Thang University )

Thursday 18th November, 2021 14:00-15:00 Room 110/ZOOM (ID: 925 8062 4476)

Abstract

Vortex reconnection plays a crucial role in the energy cascade, the dynamics of the coherent vortex structures, and turbulent mixing viscous and quantum fluids. It occurs in the natural environment and relates to practical engineering applications, such as the interaction of vortex tubes behind an aircraft, the reconnection of vortex rings (VR), the turbulent mixing in combustion engines, and quantum turbulence. A comprehensive understanding of this flow phenomenon is indispensable for improving the design and controlling the relevant devices. This research investigates turbulent energy cascade associated with the collision and reconnection of two VRs initially arranged in axis-offset and orthogonal configurations at Reynolds numbers (Re) in the range of 5000–200 000. Two elliptical VRs are generated by joining each part of the first VR with another part of the second VR for the axis-offset collision, while two VRs associate to form a double U-shaped vortex, and this vortex reconnects itself at two points to form three elliptical VRs linked by the vortex filaments for the orthogonal collision. Many vortex structures in various scales and shapes, including small-scale VRs and horseshoe vortices, are observed in connection regions for both cases. As Re increases, the energy of formed small vortices raises, and their wavenumber (k) range enlarges. The flow energy spectrum approaches a k^(–5/3) slope of the Kolmogorov hypotheses at low wavenumbers. For the axis-offset collision, the energy spectrum at medium wavenumbers continuously changes from k^(–3.0) at Re = 5000 to k^(–1.8) at Re = 200 000, and the exponent (f) of the wavenumber is determined by a function as f = 0.3304ln(Re) – 5.6538. Meanwhile, the energy spectrum at two medium-wavenumber subranges for the orthogonal collision with Re >= 20 000 approaches the slopes of k^(–3.0) and k^(–2.6). Turbulent mixing performance due to the axis-offset collision of two vortex rings is better than that with the orthogonal one.

Add to your calendar

Download event information as iCalendar file (only this event)