Experimental investigation on interactions among fluid and rod‐like particles in a turbulent pipe jet by means of particle image velocimetry

for industrial applications, where particle concentration within the flow represents a key factor, such as combustion devices (Longmire and Eaton 1992). On the other hand, turbulent modulation induced by the dispersed phase in the flow, which represents the focus of the current study, in addition to industrial applications, has also interest in turbulence fundamentals. This topic has been the subject of several works (Parthasarathy and Faeth 1990; Kussin and Sommerfeld 2002; Paris and Eaton 2001 among others), and a comprehensive review is given in Balachandar and Eaton (2010). Gore and Crowe (1989) proposed a single parameter to characterize the dispersed phase effects on the turbulence intensity of the fluid phase. This parameter is the ratio d/L of the solid phase average diameter, d, to the characteristic eddy length scale L of the fluid phase. For d/L > 0.1, the turbulence intensity is supposed to be enhanced by the solid phase, whereas for d/L < 0.1, a decrease is expected (Gore and Crowe 1989). The motivation is that the drag force on particles whose diameter is smaller than the most energetic eddies dampens the turbulence intensity, whereas bigger particles produce wakes which can increase turbulence. A historically important class of turbulent two-phase flows is represented by jets, which can be also found in several areas of engineering involving mixing, combustion and exhausting devices and represent a baseline case and a starting point for approaching more complex flows. Even for such a flow field, many works have been developed focusing on turbulence modification induced by solid particles. Fleckhaus et al. (1987) and Prevost et al. (1996) investigated experimentally the effect of particles dispersed in a gaseous jet finding that turbulence attenuation increases with particles size, in particular in the far field. Mergheni et al. (2009) and Sadr and Klewicki (2005) focused on coaxial jets, and they compared the results to Abstract The near field of a turbulent circular pipe jet laden with rigid rod-like particles is investigated experimentally by means of particle image velocimetry. Two mass fraction loadings are examined at a Reynolds number equal to 9,000. A simple and robust phase discrimination scheme based on image intensity threshold is presented and validated. Simultaneous flow and dispersed phase velocities data are discussed and compared to literature data for spherical and elongated particles providing insight on phase interactions. Being the Stokes number around unity, both inertial and dynamical effects have high relevance, the former giving rise to velocity lag among particles and fluid and the latter to turbulence modulation in the carrier flow induced by the dispersed phase.