| Dense particles tend to cluster in turbulent flows due to their inertia. I will describe experimental studies of water droplet clustering in a turbulent wind tunnel using phase Doppler interferometery (PDI). The turbulent flow was generated by active grid and is nearly homogenous and isotropic while the droplets are generated via air-atomizing spray and have a broad size. The advantage of PDI is the ability to measure size of individual drops apart from their velocities and arrival times. From these, we characterize the clustering of droplets by evaluating their radial distribution function (RDF) and study how that is related to dynamic parameters of the problem (Stokes number, Reynolds number and gravitational settling parameter). I will present the major experimental results on the clustering phenomena and make comparisons with results from theories and direct numerical simulations (DNS). If time permit, I will discuss difficulties that prevent direct comparison of results from various groups of scientists working on the same problem (due to the different methods of analysis used) and the need for a more unified effort on the problem. |
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