Experimental Study of Inertial Particle-Pair Relative Velocity in Isotropic Turbulence
MetadataShow full item record
The investigation of turbulence-enhanced inertial particle collision in isotropic turbulence could improve our understanding and modeling of many particle-laden turbulent flows in engineering and nature. In this study, we investigate one of the most critical factors of particle collision – particle-pair relative velocity (RV) in three major steps. First, to generate a reliable homogeneous and isotropic turbulence (HIT) field, we have designed and implemented a high Reynolds number ( R λ ), enclosed, fan-driven HIT chamber in the shape of ‘soccer ball’, conducive for studying inertial particle dynamics using whole-field imaging techniques. The characterization of turbulence in this near-zero-mean flow chamber was performed using a new two-scale particle imaging velocimetry (PIV) approach. The measurement results showed that turbulence in the apparatus achieved high homogeneity and isotropy in a large central region (48mm diameter) of the chamber with minimized gravity effect. A maximum R λ of 384 was achieved. Second, to measure particle-pair RV accurately, we have employed numerical experiments to systemically analyze the measurement error in the previous particle-pair RV measurement by holographic PIV. We found that accurate RV measurement requires high accuracy of both particle positioning and particle pairing. To meet these requirements, we have devised a novel planar 4-frame particle tracking velocimetry technique (4F-PTV) combining two PIV systems. It tracks particles in four consecutive frames in high speed to increase particle pairing accuracy. Furthermore, the particles are tracked only in a thin laser light sheet, thus negating the intrinsic position uncertainty in the depth direction in holographic PIV. In addition, we have studied the laser thickness effect on the RV measurement and attempted to use Monte Carlo analysis to correct this effect. Third, and most importantly, to better understand turbulence-enhanced inertial particle collision, we have systematically investigated the effects of Reynolds number and Stokes number ( St ) on particle-pair RV using the planar 4F-PTV technique in the HIT chamber. Two experiments were performed: varying R λ between 246 and 357 at six fixed St values, and varying St between 0.02 and 4.63 at five fixed R λ values. Measured mean inward particle-pair RV ⟨ w r – ⟩ as a function of separation distance r were compared against DNS under closely matched conditions. At all experimental conditions, an excellent agreement was achieved except when particle separation distance r<∼10 η ( η : Kolmogorov length scale), where experimental ⟨ w r – ⟩ was consistently higher, possibly due to particle polydispersity and finite laser thickness in experiment. Through these three steps, we found that, at any fixed St, the mean inward particle-pair RV, ⟨ w r – ⟩ was essentially independent of R λ , echoing DNS findings by Ireland et al. (2016a). At any fixed R λ , ⟨ w r – ⟩ increased with St at small r , showing dominance of the path-history effect in the dissipation range when St ≥ O (1), but decreased with St at large r , indicating dominance of the inertial filtering effect. What I provided here are the first experimental observation of the independence of mean inward particle-pair RV on Reynolds number, and the first experimental observation of these two mechanisms on the mean inward particle-pair RV over a large range of particle separation distances.
Showing items related by title, author, creator and subject.
Multiple Particle Types for Modeling Particle - Associated Contaminant Transport: Towards a Particle Based Transport Model for Hydrophobic Organic Chemicals in Aquatic Systems Hu, Sheng (2011)This research is designed to investigate the potential need to incorporate multiple particle types, rather than a single particle type, to accurately model particle associated hydrophobic contaminant transport in aquatic ...
Insoluble Particles in the GISP2 Ice Core: (a) Analysis of Core Stratigraphy by Laser-Light Scattering (b) Changes in Minerology and Particle Size in Glacial Ice Michael Ram Principal Investigator (2014-04-02)9322401 Ram This award is for support for a three year project to complete measurements of stratigraphy on the Greenland Ice Sheet Project Two (GISP2) ice core with laser-light scattering, using both a solid technique and ...
Study on effect of charge on inertial particle motion in turbulence by using holographic particle tracking velocimetry Yang, Fan (2014)Particles in turbulence flows, either natural or artificial, can be charged. According to the previous research, electrical charge on particles has an influence on both rain enhancement and particle clustering in turbulent ...