Analysis of Turbulence Characteristics in Two Large Concentric Annular Ducts Through Particle Image Velocimetry

Abstract

An experimental study is presented on water single-phase flow in two 10.5 m-long annular ducts, with external pipe's internal diameter (De) of 155 mm and two concentric internal pipes of external diameters (Di) of 60 mm and 125 mm, i.e., radius ratio (α = Ri/e) of 0.39 and 0.80, respectively, with the aim of improving the understanding of flows in annular ducts. Particle image velocimetry (PIV) was applied to obtain instantaneous and averaged velocity measurements of the flow field. A charge-coupled device camera (2448 pixel × 2050 pixel, 5 Mpixel, 12-bit ) recorded pairs of images of the seeding particles and a double-pulsed PIV laser (Nd:YAG, frequency doubled to 532 nm), with a measured pulse intensity of 70 to 75 mJ/pulse, provided the illumination. Laminar flows were analyzed for validation purposes, experimental data on turbulent flows were compared with the classical law of the wall of the turbulent boundary-layer model, and the shear stresses derived from PIV data were compared with those calculated from the measured pressure drop. The effects of the Reynolds number and geometry on turbulent velocity profiles and Reynolds stresses are presented. The results suggest that the law of the wall for annular-duct flow is a function of radius ratio. The new experimental results are of great value for the development of computational fluid dynamics models and more refined pressure-drop prediction tools in annular-duct flow.