Laboratory experiments for intense vortical structures in turbulence velocity fields

圆顶宽顶堰上方的旋涡流动结构

The structure of vortical flow over a rounded broad-crested weir

本研究通过DES和LES模拟结合水槽实验，探究圆顶宽顶堰上方湍流的相干涡与自由水面相互作用，明确了流动特性，且发现上游设置人工水池可降低86%的水面波动效应。

Vortex Tubes in Turbulence Velocity Fields at High Reynolds Numbers

The elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in laboratory experiments for boundary layers and duct flows at microscale Reynolds numbers 332-1934. While past experimental studies focused on intense vortex tubes, the present study focuses on all vortex tubes with various intensities. We obtain the mean velocity profile. The radius scales with the Kolmogorov length. The circulation velocity scales with the Kolmogorov velocity, in contrast to the case of intense vortex tubes alone where the circulation velocity scales with the rms velocity …

Coherent vortex structures in quantum turbulence

This report addresses an important question discussed by the quantum turbulence community during the last decade: do quantized vortices form, in zero-temperature superfluids, coherent structures similar to vortex tubes in ordinary, viscous turbulence? So far the evidence provided by numerical simulations is that bundles of quantized vortices appear in finite-temperature superfluids, but from the interaction with existing coherent structures in the turbulent (viscous) normal fluid, rather than due to the intrinsic superfuid dynamics. In this report we show that, in very intense quantum turbulen…

Dynamics of a long chain in turbulent flows: Impact of vortices

We show and explain how a long bead-spring chain, immersed in a homogeneous, isotropic turbulent flow, preferentially samples vortical flow structures. We begin with an elastic, extensible chain which is stretched out by the flow, up to inertial-range scales. This filamentary object, which is known to preferentially sample the circular coherent vortices of two-dimensional (2D) turbulence, is shown here to also preferentially sample the intense, tubular, vortex filaments of 3D turbulence. In the 2D case, the chain collapses into a tracer inside vortices. In 3D, on the contrary, the chain is ext…

Three-dimensional structure of the flow inside the left ventricle of the human heart

The laboratory models of the human heart left ventricle developed in the last decades gave a valuable contribution to the comprehension of the role of the fluid dynamics in the cardiac function and to support the interpretation of the data obtained in vivo. Nevertheless, some questions are still open and new ones stem from the continuous improvements in the diagnostic imaging techniques. Many of these unresolved issues are related to the three-dimensional structure of the left-ventricular flow during the cardiac cycle. In this paper we investigated in detail this aspect using a laboratory mode…

Dissipation anomaly in a turbulent quantum fluid

When the intensity of turbulence is increased (by increasing the Reynolds number, e.g. by reducing the viscosity of the fluid), the rate of the dissipation of kinetic energy decreases but does not tend asymptotically to zero: it levels off to a non-zero constant as smaller and smaller vortical flow structures are generated. This fundamental property, called the dissipation anomaly, is sometimes referred to as the zeroth law of turbulence. The question of what happens in the limit of vanishing viscosity (purely hypothetical in classical fluids) acquires a particular physical significance in the…

High-resolution direct simulation of deep water breaking waves: transition to turbulence, bubbles and droplet production

[Abridged]We present high-resolution three-dimensional direct numerical simulations of breaking waves solving the two-phase Navier-Stokes equations. We investigate the role of the Reynolds and Bond numbers on the energy, bubble and droplet statistics of strong plunging breakers, and explore the asymptotic regimes at high Reynolds and Bond numbers to be compared with laboratory breaking waves. Energetically, the breaking wave transitions from laminar to three-dimensional turbulent flow on a timescale that depends on the turbulent Reynolds number up to a limiting value of $Re_λ\sim 100$, consist…

可压缩湍流边界层中近壁湍流结构与重粒子之间的相互作用

Interactions between the near-wall turbulent structures and heavy particles in compressible turbulent boundary layers

本文通过马赫数6载重粒子可压缩湍流边界层的直接数值模拟，揭示粒子质量载荷削弱近壁胀压运动但表面摩擦变化仍主要由无散雷诺剪切应力控制。

二维湍流的有效输运：涡旋气体理论与尺度不变逆级联的对比

Effective transport by 2D turbulence: Vortex-gas theory vs. scale-invariant inverse cascade

本文研究二维湍流有效扩散率，发现尺度不变逆级联标度失效，并提出由孤立涡旋及涡核局部耗散主导的替代标度律，且与DNS定量一致。