This DNS study is focused on the structure of turbulence in a boundary layer. First, it is not appropriate to call the turbulent flow as a “random” motion. Any mean flow like Blasius solution, which is a Navier-Stokes solution, added by white noise or random perturbation would be rejected by Navier-Stokes equations and the perturbation will be damped quickly. The governing Navier-Stokes equatio...

We consider the system of the N vortex points with the identical strength on a sphere. As a local effect of the rotation of the sphere, we fix vortex points at the both poles, which are called the pole vortices. When the N vortex points are equally spaced along the line of latitude of the sphere, the configuration is called the “N -ring” or “N -gon”. It is a relative fixed configuration[3,4] an...

Background Vortex formation in the left ventricle (LV) is suggested to contribute to efficient blood pumping and altered vortex formation is associated with diastolic dysfunction. Patients after atrioventricular septal defect (AVSD) correction present abnormalities in valve morphology and subsequently develop altered inflow patterns (Calkoen et al. JMRI 2014), which may disturb normal vortex fo...

In this paper, the mechanism of momentum deficit formation about the vortex legs is deeply studied. A new mechanism on how the multiple rings are formed one by one is presented. It is found that the momentum deficit is generated by vortex ring leg ejection. The momentum deficit forms shear layers above the vortex legs. The shear layers finally form new vortex rings one by one.

Superfluidity is a special state of matter exhibiting macroscopic quantum phenomena and acting like a fluid with zero viscosity. In such a state, superfluid vortices exist as phase singularities of the model equation with unique distributions. This paper presents novel techniques to aid the visual understanding of superfluid vortices based on the state-of-the-art non-linear Klein-Gordon equatio...

This article gives an overview of growing knowledge of translation speed of an axisymmetric vortex ring, with focus on the influence of viscosity. Helmholtz-Lamb’s method provides a short-cut to manipulate the translation speed at both small and large Reynolds numbers, for a vortex ring starting from an infinitely thin core. The resulting asymptotics significantly improve Saffman’s formula (197...

We capture the decay of a quantized vortex ring in superfluid helium-4 by imaging particles trapped on the vortex core. The ring shrinks in time, providing direct evidence for the dissipation of energy in the superfluid. The ring with trapped particles collapses more slowly than predicted by an available theory, but the collapse rate can be predicted correctly if the trapping of the particles o...

The behavior of small-scale propellers operating in vertical descent and through the vortex ring state (VRS) was measured. In particular, a total of 26 propellers with diameters ranging from 9 to 11 in. (0.229 to 0.279 m) were tested in the University of Illinois at Urbana-Champaign (UIUC) 2.8×4 ft (0.853×1.219 m) low-turbulence wind tunnel at low Reynolds numbers to measure the propeller thrus...