Breakdown of the Laminar Flow Regime in Permeable-Walled Ducts

Abstract

The stability of laminar flow in a parallel-plate channel having one permeable bounding wall is investigated by means of linear theory. The analysis takes account of the coupling of the disturbance fields in the channel and in the permeable material and of velocity slip at the surface of the permeable wall. Complementary experiments are performed in which the breakdown of the laminar regime in flat rectangular ducts is identified from pressure-drop measurements and from flow visualization studies. The experiments cover the range of slip velocities from 15–30 percent of the mean velocity and, in addition, the case of zero slip (impermeable walls). In the slip range of the experiments, the instability Reynolds number results of both analysis and experiment lie below the corresponding values for the case of the impermeable-walled duct. Furthermore, in this range, the instability Reynolds numbers are rather insensitive to variations in the slip velocity. Quantitative agreement between analysis and experiment was found to be somewhat better in the slip range than for the impermeable-walled duct.