PIV measurements of water mist transport in a homogeneous turbulent flow past an obstacle

Abstract

To obtain a better understanding of the physical processes involved in liquid suppressant transport in cluttered spaces, particle image velocimetry (PIV) measurements were carried out in the droplet-laden, grid-generated, homogeneous turbulent flow over both an unheated and heated cylinder, and a body-centered cube (BCC) arrangement of spheres. Transport of both water droplets and aerosol particles was characterized upstream and downstream of these obstacles. Data were recorded for the cylinder at ambient and elevated temperatures (at 423 K) to estimate the effects of the hot cylinder surface on droplet transport. The results indicated that smaller droplets are entrained into the recirculation region behind the cylinder while the larger droplets impact the cylinder surface, accumulate and drip off, and/or rebound off the surface and disperse into the free stream. The flow over the heated cylinder resulted in the formation of a vapor layer on the downstream side of the cylinder in the shear region between the recirculation zone and free stream. Thus, vaporization of larger droplets impinging on the heated cylinder surface suggests an increased probability of vapor. For the BCC (with a blockage ratio of about 64%), there was both transport of droplets and seed particles around and through the BCC, as well as significantly more liquid accumulation and dripping than for the cylinder.