Slow flow through a brush

This paper reports velocity measurements of slow flow through a model brush. The flow field was created in the annulus between two concentric cylinders, which was filled with a viscous oil. The inner cylinder was stationary and the outer one was installed on a turntable and rotated at a constant speed. A brush was modeled by an array of uniformly spaced rods mounted horizontally onto the inner cylinder. With a generous gap between the rod ends and the outer cylinder, the flow outside the array was circular Couette flow. Three brushes were made and the external shear flow penetrated these because the solid volume fractions were small, namely, 0.025, 0.05, and 0.10. Particle image velocimetry was used to study the velocity field in the penetration region, and from these measurements the velocity at the interface, "the slip velocity," was determined. The slip velocity was found to be close to the value predicted by Brinkman's equation, and to be higher than velocities found previously for rod arrays in other configurations. (C) 2004 American Institute of Physics.