Experimental investigation of inertial particle dynamics in isotropic turbulence using hybrid digital holographic imaging
Quantification of the inertial particle clustering and the dispersion and collision processes is of fundamental importance to the validation of our theoretical understanding of the dynamics of inertial particles in both natural and industrial turbulent flows. The particle collision kernel contains two important parameters, the radial distribution function (RDF) and the mean inward radial relative velocity (Sundaram and Collins, 1997). The sensitivity of these parameters on the particle inertia or Stokes number and the turbulence characteristic namely the Reynolds number based on the Taylor microscale, R λ , is key to advancing our understanding of the phenomena. Due to the complicated physics of the particle collision process it is typically studied using direct numerical simulation (DNS). There is a pressing need to experimentally validate the DNS results as well as to extend the data to Reynolds number beyond what is currently possible. Using the hybrid digital holographic system as a tool the particle inertial effect on both RDF and two particle radial relative velocity PDF was studied in a stationary, homogenous and isotropic turbulent box experimentally and compared with DNS. The optical set was modified to improve the quality of the holograms and then optimized to minimize the error in the depth position accuracy use mono dispersed particles scattered on the glass plate. By analyzing the angular aperture theoretically and experimentally it was determined to be limited by the long focal length microscopic lens system. Three inertial particles were employed to obtain 3 different Stokes numbers. The PDF and RDF were quantified using two different particle matching and two calculation methods to compare their performance. Finally the Stokes number effects on the two particle radial relative velocity PDF and RDF were compared with DNS results under similar flow and particle Stokes number conditions.