Characterization of the Flow Field inside a Rotating, Rib-Roughened, U-Shaped Channel using Particle Image Velocimetry

A research program was initiated at ONERA with the aim to improve the understanding of aerodynamic and thermal phenomena of internal blade cooling by forced convection and to incorporate this knowledge into predictive tools. As part of this ongoing program, this paper addresses the use of the Particle Image Velocimetry technique to characterize flow fields inside a rotating, square cross-section, rib-roughened U-shaped channel that models the blade coolant passage. Results obtained for internal walls equipped with square profile ribs, inclined at 60° to the main flow direction, are compared with those obtained for smooth walls. For the centrifugal branch of the smooth channel, PIV measurements revealed a shift of maximum axial velocity toward the trailing edge, which is consistent with the enhancement of the convective heat transfer along this wall as reported in the literature. In the centripetal branch, the secondary flow resulting from added effects of the 180°-bend and rotation consisted in a single vortex. The presence of the ribs induced the formation of two counter-rotating vortices symmetric with respect to the channel vertical mid-section. In rotation, these vortices combined with the two classical counter-rotating vortices generated from the Coriolis force into a large single vortex structure.