Intensified and attenuated waves in a microbubble Taylor–Couette flow

Abstract

The effect of the presence of microbubbles on a flow state is experimentally investigated in a Taylor–Couette flow with azimuthal waves, in order to examine the interaction mechanism of bubbles and flows that result in drag reduction. The average diameter of the bubbles is 60 μm, which is smaller than the Kolmogorov length scale, and the maximum void fraction is 1.2 × 10−4 at the maximum case. The modifications of the fluid properties, bulk density, effective viscosity, and the extra energy input caused by the addition of microbubbles are expected to have a small effect on modifying flow states. The power of the basic wave propagating in the azimuthal direction is enhanced; its modulation, however, is decreased by adding microbubbles in the flow regime corresponding to modulated Taylor vortex flow. Moreover, the gradient of the azimuthal velocity near the walls, source of the wall shear stress, decreases by 10%. The modified velocity distribution by adding microbubbles is comparable to that obtained with a 20% lower Reynolds number. Microbubbles in the coherent structure of the wavy Taylor vortices are visualized and exhibit a preferential distribution and motion at the crests and troughs of the waviness. The roles of the inhomogeneously distributed microbubbles in wavy vortical structures are discussed in view of our findings.