The influences of jet precession on large-scale instantaneous turbulent particle clusters

An experimental investigation of the influence of jet precession on the formation of large-scale instantaneous turbulent particle clusters is reported. Instantaneous planar particle distributions in the first seven nozzle diameters downstream from a simulated pulverised fuel burner have been measured using planar nephelometry, a laser-based instantaneous concentration technique. Large-scale instantaneous particle clusters (ITPCs) are identified and quantified from these data. A systematic study is conducted to assess the influence of the ratio of the precessing jet to axial momentum streams on ITPCs. The results show that ITPCs can be modified by this momentum ratio. The average size of ITPCs reaches a maximum for cases with high precessional momentum, although excessive precessional momentum can reduce ITPC size. The particle number density per unit area inside these ITPCs reaches a maximum for an intermediate value of jet precession. The spread of ITPC centroids can be estimated from the mean jet spread of particles and therefore increases with increasing precessing jet momentum once above a certain threshold.