Buoyancy Profile Inhibition of Turbulence in Nearly Vertical Bubbly Shear Flow

Abstract

We report mea.sUICJD.CD.ts of two-dimensional (B/D::S) fully tw:bulent and developed duct flows (overall length/depth. IlD=60; D-based Reynolds number Re>104) for inclinations to 30 degrees from vertical at low voidagcs (<5% sectional average) representative of disperse regime using tap water bubbles ( 4-6 mm) and smaller bubbles (2 mm) stabilised in ionic solution. Pitot and static probe instrumentation, primitive but validated, provided adequate (10% local value) discrimination of main aspects of Che mean velocity and voidage profiles at representative streamwise station i.e IlD =40. Our results can be divided into three categories of behavionr. For vertical flow (0 degrees) the evidence is inconclusive as to whether bubbles are preferentially trapped within the wall-layer as found in some, may be most, earlier experimental work. Thus the 4 mm bubbles showed indication of voidage retention but Che 2 mm bubbles did not. For nearly vertical flow (5 degrees) there was pronounced profiling of voidage especially with 4 mm bubbles but the Transvm e transport was not suppressed sufficiently to induce any obvious layering. In Chis context, we also refer to similarities wieh previous work on one-phase vertical and nearly vertical mixed convection flows displaying buoyancy inhibited mean shear turbulence. However, with inclined flow (10+ degrees) a distinctively layered pattem was invariably manifested in which voidage confinement increased with increasing inclination. In this paper we address flow behaviour at near vertical conditions.