Three-Dimensional Measurement of Aerosol Particle Clustering in Homogeneous Isotropic Turbulence

2003 ◽  
Author(s):  
Lujie Cao ◽  
Gang Pan ◽  
Hui Meng
Keyword(s):  
Isotropic Turbulence ◽  
Imaging System ◽  
Three Dimensional ◽  
Theoretical Models ◽  
Particle Collision ◽  
Collision Kernel ◽  
Particle Clustering ◽  
Coagulation Rate ◽  
Holographic Imaging ◽  
Preferential Concentration

Due to the inertial mismatch between dense particles and lighter surrounding gas, aerosol particles in the size range 1 to 10 μm cluster in a flow field. This phenomenon, sometimes referred to as preferential concentration, can increase the particle coagulation rate by as much as two orders of magnitude. Many direct numerical simulation (DNS) studies have been conducted to study preferential concentration and various theoretical models have been proposed to predict the effect of clustering on particle collision rate. However, to date there is very little experimental data available to validate DNS results and theoretical models. In this study, we apply our state-of-the-art holographic imaging system to measure the 3D position of particles in a turbulence chamber. Nearly homogenous isotropic turbulence is generated in the center of the chamber by use of eight fans mounted in the corners. With our holographic imaging system, individual particles can be measured simultaneously and hence we are able to calculate particle radial distribution function (RDF), a statistical measure of particle clustering and a key variable in collision kernel. In this paper we report the first experimental 3D RDF to date. Comparison between our 3D RDF and 2D RDF results shows that significant bias exists in experimental results obtained using 2D experimental techniques.

Experimental and numerical investigation of inertial particle clustering in isotropic turbulence

2008 ◽  
Vol 600 ◽  
pp. 245-256 ◽  
Author(s):  
JUAN P. L. C. SALAZAR ◽  
JEREMY DE JONG ◽  
LUJIE CAO ◽  
SCOTT H. WOODWARD ◽  
HUI MENG ◽  
...  
Keyword(s):  
Isotropic Turbulence ◽  
Three Dimensional ◽  
Experimental System ◽  
Collision Kernel ◽  
Inertial Particle ◽  
Particle Clustering ◽  
Glass Spheres ◽  
Preferential Concentration ◽  
Particle Imaging ◽  
Good Agreement

This paper presents the first detailed comparisons between experiments and direct numerical simulations (DNS) of inertial particle clustering in nearly isotropic ‘box turbulence’. The experimental system consists of a box 38cm in each dimension with fans in the eight corners that sustain nearly isotropic turbulence in the centre of the box. We inject hollow glass spheres with a mean diameter of 6 μm and measure the locations of several hundred particles in a 1 cm3 volume in the centre of the box using three-dimensional digital holographic particle imaging. We observe particle concentration fluctuations that result from inertial clustering (sometimes called ‘preferential concentration’). The radial distribution function (RDF), a statistical measure of clustering, has been calculated from the particle position field. We select this measure because of its relevance to the collision kernel for particles. DNS of the equivalent system, with nearly perfect parameter overlap, have also been performed. We observe good agreement between the RDF predictions of the DNS and the experimental observations, despite some challenges in the interpretation of the experiments. The results provide important guidance on ways to improve the measurement.

Low-cost three-dimensional millimeter-wave holographic imaging system based on a frequency-scanning antenna

2017 ◽  
Vol 57 (1) ◽  
pp. A65
Author(s):  
Vahid Amin Nili ◽  
Ehsan Mansouri ◽  
Zahra Kavehvash ◽  
Mohammad Fakharzadeh ◽  
Mahdi Shabany ◽  
...  
Keyword(s):  
Millimeter Wave ◽  
Imaging System ◽  
Low Cost ◽  
Three Dimensional ◽  
Holographic Imaging ◽  
Frequency Scanning ◽  
Scanning Antenna

scholarly journals Spectral selective fluorescence molecular imaging with volume holographic imaging system

2016 ◽  
Vol 09 (02) ◽  
pp. 1650010 ◽  
Author(s):  
Yanlu Lv ◽  
Jiulou Zhang ◽  
Fei Liu ◽  
Junwei Shi ◽  
Huizhi Guang ◽  
...  
Keyword(s):  
Imaging System ◽  
Three Dimensional ◽  
Field Of View ◽  
Lateral Field ◽  
Holographic Imaging ◽  
Target Spectrum ◽  
Diffusive Medium ◽  
Fluorescence Images ◽  
3D Information ◽  
Phantom Experiments

A compact volume holographic imaging (VHI) method that can detect fluorescence objects located in diffusive medium in spectral selective imaging manner is presented. The enlargement of lateral field of view of the VHI system is realized by using broadband illumination and demagnification optics. Each target spectrum of fluorescence emitting from a diffusive medium is probed by tuning the inclination angle of the transmission volume holographic grating (VHG). With the use of the single transmission VHG, fluorescence images with different spectrum are obtained sequentially and precise three-dimensional (3D) information of deep fluorescent objects located in a diffusive medium can be reconstructed from these images. The results of phantom experiments demonstrate that two fluorescent objects with a sub-millimeter distance can be resolved by spectral selective imaging.

Hybrid digital holographic imaging system for three-dimensional dense particle field measurement

2008 ◽  
Vol 47 (25) ◽  
pp. 4501 ◽  
Author(s):  
Lujie Cao ◽  
Gang Pan ◽  
Jeremy de Jong ◽  
Scott Woodward ◽  
Hui Meng
Keyword(s):  
Field Measurement ◽  
Imaging System ◽  
Three Dimensional ◽  
Dense Particle ◽  
Particle Field ◽  
Holographic Imaging

scholarly journals The effect of Reynolds number on inertial particle dynamics in isotropic turbulence. Part 2. Simulations with gravitational effects

2016 ◽  
Vol 796 ◽  
pp. 659-711 ◽  
Author(s):  
Peter J. Ireland ◽  
Andrew D. Bragg ◽  
Lance R. Collins
Keyword(s):  
Reynolds Number ◽  
Single Particle ◽  
Isotropic Turbulence ◽  
Distribution Functions ◽  
Particle Collision ◽  
Collision Kernel ◽  
Finite Domain ◽  
Inertial Particles ◽  
Inertial Particle ◽  
Wide Range

In Part 1 of this study (Ireland et al., J. Fluid Mech., vol. 796, 2016, pp. 617–658), we analysed the motion of inertial particles in isotropic turbulence in the absence of gravity using direct numerical simulation (DNS). Here, in Part 2, we introduce gravity and study its effect on single-particle and particle-pair dynamics over a wide range of flow Reynolds numbers, Froude numbers and particle Stokes numbers. The overall goal of this study is to explore the mechanisms affecting particle collisions, and to thereby improve our understanding of droplet interactions in atmospheric clouds. We find that the dynamics of heavy particles falling under gravity can be artificially influenced by the finite domain size and the periodic boundary conditions, and we therefore perform our simulations on larger domains to reduce these effects. We first study single-particle statistics that influence the relative positions and velocities of inertial particles. We see that gravity causes particles to sample the flow more uniformly and reduces the time particles can spend interacting with the underlying turbulence. We also find that gravity tends to increase inertial particle accelerations, and we introduce a model to explain that effect. We then analyse the particle relative velocities and radial distribution functions (RDFs), which are generally seen to be independent of Reynolds number for low and moderate Kolmogorov-scale Stokes numbers $St$. We see that gravity causes particle relative velocities to decrease by reducing the degree of preferential sampling and the importance of path-history interactions, and that the relative velocities have higher scaling exponents with gravity. We observe that gravity has a non-trivial effect on clustering, acting to decrease clustering at low $St$ and to increase clustering at high $St$. By considering the effect of gravity on the clustering mechanisms described in the theory of Zaichik & Alipchenkov (New J. Phys., vol. 11, 2009, 103018), we provide an explanation for this non-trivial effect of gravity. We also show that when the effects of gravity are accounted for in the theory of Zaichik & Alipchenkov (2009), the results compare favourably with DNS. The relative velocities and RDFs exhibit considerable anisotropy at small separations, and this anisotropy is quantified using spherical harmonic functions. We use the relative velocities and the RDFs to compute the particle collision kernels, and find that the collision kernel remains as it was for the case without gravity, namely nearly independent of Reynolds number for low and moderate $St$. We conclude by discussing practical implications of the results for the cloud physics and turbulence communities and by suggesting possible avenues for future research.

scholarly journals A Low-Cost and Compact Three-Dimensional Microwave Holographic Imaging System

Electronics ◽  
2019 ◽  
Vol 8 (9) ◽  
pp. 1036 ◽  
Author(s):  
Hailun Wu ◽  
Reza K. Amineh
Keyword(s):  
Imaging System ◽  
Low Cost ◽  
Three Dimensional ◽  
Cost Effective ◽  
Microwave Imaging ◽  
Destructive Testing ◽  
Holographic Imaging ◽  
Compact Size ◽  
Vector Network Analyzers ◽  
Network Analyzers

With the significant growth in the use of non-metallic composite materials, the demands for new and robust non-destructive testing methodologies is high. Microwave imaging has attracted a lot of attention recently for such applications. This is in addition to the biomedical imaging applications of microwave that are also being pursued actively. Among these efforts, in this paper, we propose a compact and cost-effective three-dimensional microwave imaging system based on a fast and robust holographic technique. For this purpose, we employ narrow-band microwave data, instead of wideband data used in previous three-dimensional cylindrical holographic imaging systems. Three-dimensional imaging is accomplished by using an array of receiver antennas surrounding the object and scanning that along with a transmitter antenna over a cylindrical aperture. To achieve low cost and compact size, we employ off-the-shelf components to build a data acquisition system replacing the costly and bulky vector network analyzers. The simulation and experimental results demonstrate the satisfactory performance of the proposed imaging system. We also show the effect of number of frequencies and size of the objects on the quality of reconstructed images.

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