3D reconstruction of the flow and vortical field in a rotating sharp “U” turn channel

Abstract

Particle image velocimetry experiments have been carried out to obtain visualizations and measurements of the main and secondary flow fields in a square channel with a sharp ''U'' turn. Both the main and the secondary flow fields have been used to perform a 3D reconstruction of the mean flow and vortical fields in the turn region and in the outlet duct. In order to study the influence of the rotation, tests both in stationary (absence of rotation, Re = 20,000) and in rotating (Re = 20,000 and Ro = 0.3) conditions have been performed. The results show that the Coriolis and centrifugal forces, caused by the rotation, yield strong modifications to the symmetrical flow and vortical fields that are generated, in the static case, only by the abrupt inversion of the flow direction. Abbreviations 3D Three-dimensional CCD Charge-coupled device LASER Light amplification by stimulated emission of radiation LDA Laser doppler anemometry Nd:YAG Neodymium yttrium aluminium garnet PIV Particle image velocimetry List of symbols C Circuit used to the evaluation of the vorticity components D Channel hydraulic diameter l Direction normal to the planar surface S Re Reynolds number Ro Rotation number S Planar surface bounded by the circuit C U Fluid mean velocity u, v, w Mean velocity components u 0 , v 0 Turbulence intensity u* Wall friction velocity u 1 , w 1 Mean velocity components obtained from the images acquired with the rotating channel (Re = 20,000, Ro = 0.3) u 2 , w 2 Mean velocity components obtained from the images acquired with the rotating channel and the fluid at rest U 2 , W 2 Velocity components of V pp u g , v g , w g Mean velocity components relative to the 3D grids V Local velocity vector V Local velocity module V pp Rotation peripheral velocity relative to the generic point of the investigated plane W 2m Spatial average of the mean (in time) velocity component w 2 distribution obtained from the images acquired with the rotating channel and with the fluid at rest x, y, z Cartesian spatial coordinates x c , z c Cartesian spatial coordinates of the channel rotation centre a Rotation angle Electronic supplementary material The online version of this article (

PIV flow measurements for a rotating square smooth channel heated by basically uniform heat flux

“…The length of the primary separation bubble decreases monotonically with the increase of rotation on leading side. Gallo and Astarita [16], Sante and Braembussche [17] all investigated the mainstream field in rotating channels. Gallo performed a reconstruction and vertical field of the mainstream to study the influence of rotation by PIV.…”

Thermo-fluid-dynamic analysis of the flow in a rotating channel with a sharp “U” turn

“…For the rotating case, the distributions of the mean velocity components have been obtained adopting two different procedures for the yz-and xz-planes, whose detailed description is provided in a previous work of the same authors (Gallo and Astarita 2010). …”

Experimental investigation of turbulent flow in a two-pass channel with different U-shaped bends

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