Numerical and experimental analysis of poly-dispersion effects on particle-laden jets

This study presents experimental measurements and computational modelling of particle-laden jets for a wide range of Stokes numbers to analyse the effect of polydispersity on particle volume fraction and velocity. The polydisperse two-phase turbulent jet issues from a pipe into a low velocity coflow, resulting in inlet Stokes numbers, Stin, ranging from 0.003 to 25. The particle velocity and volume fraction are experimentally measured using digital particle image velocimetry and planar nephelometry simultaneously. The simulations are conducted using a newly developed model based on the probability density function of the population balance equation (PDF-PBE) in a large eddy simulation framework. A stochastic Monte Carlo method is adopted to solve the PDFPBE on an ensemble of notional Lagrangian particles, while the method of Stokes binning is employed to explicitly treat inertial effects in a computationally efficient way. There is a satisfactory agreement between the measurements and simulations. A series of monodisperse simulations were also conducted to compare with the polydisperse flows in a two-way coupled flow. The results confirm that in the monodisperse jet, small particles (with St(in) <= 0.3) closely follow the carrier phase velocity whereas in the polydisperse jet they are affected by the presence of larger particles to reduce their axial velocity decay rate. The opposite trend is observed for large particles (St(in) >= 5.5), confirming that in the polydisperse jet, the presence of small particles increases the large particles' radial dispersion that lowers their volume fraction along the centreline compared to the monodisperse jet.