论文标题

惯性驱动的湍流中的多尺度能量预算在正常和超流弹性中

Multi-scale energy budget of inertially driven turbulence in normal and superfluid helium

论文作者

Sy, Fatimata, Diribarne, Pantxo, Rousset, Bernard, Gibert, Mathieu, Bourgoin, Mickael

论文摘要

在本文中,我们使用液体$^4 $ He提出了一种新颖的流体动力实验。使用其正常(He〜i)或超氟(He〜II)相的规范振荡网格惯性地强迫该流量,从而产生统计固定的湍流。我们使用2D Lagrangian粒子跟踪在中空玻璃微角色上表征流动的湍流特性。正如示踪剂颗粒所预期的那样,粒子位置上的伏罗尼奥·特塞尔(VoronoïTeslation)并没有显着与He〜i II相中的随机泊松过程显着不同。跟踪颗粒的位置,以高时间分辨率跟踪,从而可以在整体和惯性尺度下解决速度波动,同时正确评估噪声贡献。此外,我们将颗粒的位置(通过与高斯核的卷积)区分开,以便访问少量量(例如加速度)。使用这些测得的数量和经典均匀的各向同性湍流(hit)的形式主义,以跨尺度执行能量预算,我们以大规模提取能量注射速率,通过惯性尺度层叠的能量通量,降低到耗散的小尺度。我们发现,在这种惯性驱动的湍流中,无论流体的正常或超流体状态如何,在不同尺度上的能量估计相互兼容,并且与文献中正常流体报告的振荡网格湍流结果一致。最大的差异显示在小尺度上,信号与噪声比更难控制,以及2D测量受流量的3D性质污染的位置。这促使将来的实验项目集中在小尺度,低噪声和3D测量上。

In this paper we present a novel hydrodynamic experiment using liquid $^4$He. The flow is forced inertially by a canonical oscillating grid using either its normal (He~I) or superfluid (He~II) phase, generating a statistically stationary turbulence. We characterise the turbulent properties of the flow using 2D Lagrangian Particle tracking on hollow glass micro-spheres. As expected for tracer particles, the Voronoï tessellation on particle positions does not show a significant departure from a random Poisson process neither in He~I nor He~II phase. Particles' positions are tracked with high temporal resolution, allowing to resolve velocity fluctuations at integral and inertial scales while properly assessing the noise contribution. Additionally, we differentiate the particles' positions (by convolution with Gaussian kernels) in order to access small scale quantities like acceleration. Using these measured quantities and the formalism of classical Homogeneous Isotropic Turbulence (HIT) to perform an energy budget across scales we extract the energy injection rate at the large scale, the energy flux cascading through inertial scales, down to small scales at which it is dissipated. We found that in such inertially driven turbulence, regardless of the normal or superfluid state of the fluid, estimates of energy at the different scales are compatible with each other and consistent with oscillating grid turbulence results reported for normal fluids in the literature. The largest discrepancy shows up at small scales where the signal to noise ratio is harder to control and where the 2D measurement is contaminated by the 3D nature of the flow. This motivates to focus future experimental projects towards small scales, low noise and 3D measurements.

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