Study on vorticity structures in late flow transition

Abstract

Vorticity and vortex are two different but related concepts. This paper focuses on the investigation of vorticity generation and development, and vorticity structure inside/ outside the vortex. Vortex is a region where the vorticity overtakes deformation. Vortex cannot be directly represented by the vorticity. Except for those vorticity lines which come from and end at side boundaries, another type of vorticity, self-closed vorticity lines named vorticity rings, is numerouslygenerated inside the domain during flow transition. These new vorticity rings are found around the hairpin vortex heads and legs. The generation and growth of vorticity rings are produced by the buildup of the vortices according to the vorticity transport equation. On the other hand, vortex buildup is a consequence of vorticity line stretching, tilting and twisting. Both new vorticity and new vortices are generated during the flow transition. According to the Helmholtz vorticity flux conservation law, vorticity line cannot be interrupted, started, or ended inside the flow field, the newly produced vorticity has only one form which is the vorticity rings. In addition, an interesting finding is that a single hairpin vortex consists of several types of vorticity lines which could come from the side boundaries, whole vorticity rings and part of vorticity rings. Nomenclature M∞ = Mach number Rein = Reynolds number δin = inflow displacement thickness ∞  Corresponding author. Email address: cliu@uta.edu xin = distance between leading edge of flat plate and upstream boundary of computational domain Subscript in = inflow w = wall ∞ = free stream

Wall turbulence response to surface cooling and formation of strongly stable stratified boundary layers

“…The quasi-streamwise vortical structures are absent in the regions outside of the turbulent strip, which we refer to as quiet zones. Turbulence is concentrated in the strip, which comprises numerous quasi-streamwise vortices and hairpin like structures 56,57 . However, the quantity of lifted and detached vorticies is considerably lower in comparison with t o = 0.1, even in the turbulent strip which can explain the reduction in turbulence production from its initial value.…”

Study on the Vortex in a Pump Sump and Its Influence on the Pump Unit

“…The research on the influencing factors of a vortex can directly affect the research progress of vortex hydraulic characteristics, such as critical submerged depth and vortex elimination. Therefore, a substantial amount of research on the influencing factors of the vortex has been undertaken [7,8]. Nahale [9] believes that there is a negative pressure below a certain point on the water surface, resulting in continuous rupture of the water and air intrusion, thus forming a vortex.…”

Modified normalized Rortex/vortex identification method

“…Hence, the present new modified normalized Rortex/vortex identification method (14) can be rewritten as…”

“…In order to show that the modified normalized Rortex/vortex identification method (14) or (23) can get rid of bulging phenomenon performed by original Ω method, the data obtained by direct numerical simulation (DNS) of boundary layer transition on a flat plate at Mach number 0.5 and Reynolds number 1000 are studied. Fig.…”