The influence of Stokes number on particle clustering at the exit of a turbulent jet issuing from a long pipe

Abstract

A detailed assessment of the influence of Stokes number on particle clustering at the exit of a turbulent, mono-disperse, two-phase jet issuing from a long, round pipe into a low velocity co-flow was performed. This was achieved through the instantaneous measurement of particle distributions at the jet exit using planar nephelometry, together with a box counting method and a cluster identification scheme. The Stokes number based on the pipe diameter, SkD, was varied across two orders of magnitude between 0:3 ≤ SkD ≤ 22:4 while the Reynolds number was in the range 10; 000 ≤ ReD ≤ 40; 000. The results show that significant particle clustering occurs for SkD ≤ 5:6 and that the degree of particle clustering decreases with increasing Stokes number, becoming negligible for SkD ≳ 11:2. For cases where particle clustering is observed, the measurements reveal that they are within the pipe, close to the pipe boundaries for SkD ≲ 2:8 and close to the pipe axis for SkD ≳ 5:6. The results also indicate that particle clustering tends to occur at length scales of ≈ 0:1D, suggesting that peak particle clustering will occur at SkD = O(10-1).