Droplet clouds in a box of turbulence

湍流箱中的水滴云

• 批准号: EP/E029515/1
• 负责人: Yannis Hardalupas
• 金额: $ 57.28万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FE029515%2F1
• 关键词: Droplet; clouds; box; turbulence

Contrary to expectation, small particles suspended in a turbulent flowing gas or liquid, do not mix but segregate into regions of high and low concentrations. These patterns of segregation or clustering arise because of the way particles interact with the eddying motion of the turbulence in the gas. A turbulent flow at any instant of time may be considered as composed of eddies /vortices and regions of high straining rate between them. A particle in an eddy will be centrifuged away from the centre of the eddy whilst in a straining region it will be focused towards the centre of the strain. Particles will thus always try to skirt round the edges of vortices in the high straining regions between them and it is there that the particles will tend to accumulate. The degree of segregation depends up the particle response time compared to the scale and persistence of the eddy and since turbulence is composed of many scales there will usually be one particular scale where segregation will occur. This segregation can have a profound effect on many industrial and environmental processes (from powder production and combustion to formation and growth of nano-size particles to rain droplets in the atmosphere). In cases where the segregation is high enough, it can influence the actual dynamics of the way the turbulence is produced and dissipated and is therefore very important in the phenomenon of drag reduction. Simulation and measurement of this segregation process have revealed some interesting properties: singularities occur in the particle concentration which is highly intermittent both in space and time; particle motion in such circumstances contains a random uncorrelated component (RUM) or component of quasi Brownian motion. The origin of this RUM is not well understood but may be linked to the occurrence of singularities in the flow and the fact that particle trajectories can cross at any given point in the flow. The purpose of the work described in this proposal is two-fold: to understand and quantify these features and to establish their origin; to obtain for the first time a statistical description incorporating these features for single and two-particle dispersion. The approach we will use is called the PDF approach and is similar to the kinetic theory of gases in that we shall develop a pdf equation for one and two particle dispersion that includes the particle velocity as well as its position. In so doing we will use both experiment, and simulation to underwrite and validate our model equations. The experimental part will develop a novel facility to simulate rain in a box of turbulence , by generating a 'box' of isotropic turbulence, without mean flow, using acoustic actuators. The experiments will quantify, for the first time, pdfs of particle pair separations and velocities, correlations between particle and fluid velocities and associated statistics of the flow topology in the neighbourhood of particles. One important outcome of the proposed research will be the quantification of the evolution of the droplet size distributions due to particle agglomeration, and its correlation with the persistence and scales of the turbulent structures.

与预期相反，悬浮在湍流流动的气体或液体中的小颗粒不会混合，而是分离成高浓度和低浓度区域。这些分离或聚集模式的产生是因为颗粒与气体中湍流的涡流运动相互作用的方式。任意时刻的湍流都可以认为是由涡旋和它们之间的高应变率区域组成的。涡流中的颗粒将被离心离出涡流中心，而在应变区中，它将聚焦到应变中心。因此，粒子总是试图绕过它们之间的高应变区域中的涡旋边缘，粒子就会在那里聚集。分离的程度取决于颗粒的响应时间，与涡流的尺度和持续时间相比，由于湍流是由多个尺度组成的，因此通常会有一个特定的尺度发生分离。这种分离可对许多工业和环境过程产生深远影响(从粉末生产和燃烧到纳米颗粒的形成和生长，再到大气中的雨滴)。在分离足够高的情况下，它可以影响湍流产生和消散的实际动力学，因此在减阻现象中非常重要。对这种分离过程的模拟和测量揭示了一些有趣的性质：粒子浓度在空间和时间上都具有高度间歇性；在这种情况下粒子的运动包含一个随机不相关分量(RUM)或准布朗运动的分量。这种朗姆现象的起源还不是很清楚，但可能与流动中奇点的出现以及粒子轨迹可以在流动中的任何给定点相交的事实有关。本提案所述工作的目的有两个：了解和量化这些特征并确定它们的来源；首次获得一份纳入这些特征的单粒子和两粒子弥散的统计描述。我们将使用的方法被称为PDF方法，类似于气体运动论，因为我们将建立一个关于单颗粒和双颗粒弥散的PDF方程，其中包括颗粒速度及其位置。在这样做的过程中，我们将使用实验和模拟来支持和验证我们的模型方程。实验部分将开发一种新的设备来模拟湍流箱中的降雨，方法是使用声致动器生成一个没有平均流的各向同性湍流箱。这些实验将首次量化颗粒对分离和速度的pdf，颗粒和流体速度之间的关联，以及颗粒附近流动拓扑的相关统计。这项研究的一个重要成果将是量化颗粒团聚引起的液滴尺寸分布的演变，以及它与湍流结构的持续性和尺度的相关性。

项目成果

Preferential concentration of poly-dispersed droplets in stationary isotropic turbulence

• DOI: 10.1007/s00348-013-1525-3
• 发表时间: 2013-05
• 期刊: Experiments in Fluids
• 影响因子: 2.4
• 作者: H. Lian;G. Charalampous;Y. Hardalupas

Clustering of mono-disperse and poly-disperse particles in a box of turbulence

湍流箱中单分散和多分散颗粒的聚集

• 发表时间: 2010
• 作者: Charalampous G.

Preferential concentration of poly-dispersed droplets in a 'box of turbulence'

“湍流箱”中多分散液滴的优先集中

• 发表时间: 2014
• 作者: Lian H.

Time resolved measurements of droplet preferential concentration in homogeneous isotropic turbulence without mean flow

无平均流量的均匀各向同性湍流中液滴优先浓度的时间分辨测量

• DOI: 10.1063/1.5063673
• 发表时间: 2019-02
• 期刊: Physics of Fluids
• 影响因子: 4.6
• 作者: H. Lian;Y. Hardalupas;X.Y. Chang
• 通讯作者: X.Y. Chang

Preferential concentration of liquid droplets in a volume of homogeneous and isotropic turbulence

液滴在均匀和各向同性湍流体积中的优先浓度

• 发表时间: 2011
• 作者: Charalampous G.