The dynamics of a constrained three-vortex problem, a free point vortex pair in the velocity field of a fixed point vortex, is investigated. The underlying dynamical system is simplified using a coordinate transformation and categorized into two cases based on the zero and non-zero values of the constant of angular impulse. For each case, dynamical features of the vortex motion are studied analytically in the transformed plane, in order to completely classify the vortex motions and to understand the boundedness and periodicity of the inter-vortex distances. The theoretical predictions are also verified numerically and illustrated for various sets of initial conditions and circulations.
Wakes of upswept afterbodies are often characterized by a counter-rotating streamwise vortex pair. The unsteady dynamics of these vortices are examined with a spatio-temporally resolved Large-Eddy Simulation dataset on a representative configuration consisting of a cylinder with an upswept basal surface. Emphasis is placed on understanding the meandering motion of the vortices in the pair, including vortex core displacement, spectral content, stability mechanisms and overall rank-behavior. The first two energy-ranked modes obtained through Proper Orthogonal Decomposition(POD) of the time-resol…
Nonthermal fixed points, vortex statistics, and superfluid turbulence in an ultracold Bose gas
在二维和三维空间中分析了远离热平衡的稀薄简并玻色气体动力学的非热不动点。详细研究了以前在非微扰量子场论方法中发现的、最近被证明与涡旋动力学和超流湍流有关的普适幂律分布[Phys. Rev. B 84，020506（R）（2011）]。结果意味着解释的标度行为的独立涡激发的超流体和拓扑激发的统计可以描述的波动湍流的框架。发现在单粒子动量分布中观察到的特定标度指数与不可逆性以及波相互作用所遵守的守恒定律是一致的。此外，长波长的声学激励的涡旋轴承冷凝物，驱动的涡旋湮灭，发现遵循非热幂律。在统计模式中考虑涡的相关性，长时间偏离非热不动点与涡-反涡配对有关。所研究的非热不动点可在冷气体实验中得到。这些结果揭示了超流湍流的基本方面，并对相关现象具有很强的潜在影响，例如，在早期宇宙膨胀或夸克-胶子等离子体动力学中。
In the present note, we solved numerically the viscous vorticity equation of the initial-boundary value problem describing the classic Helmholtz phenomena of vortex interaction. In the leapfrogging of vortex pairs, we demonstrate the fact that there exists a variety of initial vortex configurations, such as the initial vortex core structures, the starting speeds, the lateral and longitudinal separations as well as the fluid viscosity. To simulate leapfrogging appears to be a straightforward task, based on the vorticity calculations for a number of initial vortices with different core structure…
Numerical simulations using the Lattice Boltzmann Method are presented of the following two-dimensional incompressible flow problem. Starting from configurations corresponding to translating inviscid equilibria, namely, the translating Föppl equilibria (counter-rotating point vortex pair, either fore or aft of a translating circular cylinder) and the translating Hill equilibria (counter-rotating point vortex pair, either fore or aft of an elliptic cylinder), viscosity is turned on for $t >0$ and the subsequent viscous interaction is simulated. The interaction is in a dynamically coupled settin…
This contribution relates to the simulation of the flow around the tip of a helicopter rotor blade in hovering flight conditions. We here propose a new methodology of framework adaptation, using a comprehensive rotor code and high-fidelity numerical simulations. We construct an equivalent fixed-wing configuration from a rotating blade, in which centrifugal and Coriolis forces are neglected. The effect of this approximation on the solution is analysed. The method is validated by a detailed comparison with wind tunnel data from the literature, concerning aerodynamic properties and tip vortex rol…
The interaction of trailing and leading vortex structures in low Reynolds number forced (varicose) jet with coflow is studied using Direct Numerical Simulation (DNS), where we report the dynamics of these vortices for a range of varying parameters. In a circular forced jet with Strouhal number 0.2, continuous formation of these vortices is observed which undergo pairing, tearing and disintegration. The forced jet is analyzed for varying frequency of forced perturbations, coflow temperature, turbulence intensity, momentum thickness, coflow intensity and Reynolds number at a constant forcing amp…
