Cylindrical Couette Flow Experiments in the Transition Regime

Abstract

Density distributions were measured in rarefied argon contained between two concentric cylinders, the inner one rotating, the outer one stationary. The experiments were performed with a Mach number near unity, based on the surface speed and surface temperature of the rotating cylinder. Particular attention was focused on obtaining data in the slip and transition regimes where the Knudsen number, defined as the ratio of the mean free path to the gap size between the cylinders, varied from 0.04 to 1.07. The density distributions were measured by observing the gas luminescence induced by the passage of a narrow beam of high energy electrons through the gas. In addition to the density measurements, heat transfer and drag measurements were also made in order to estimate the values of the thermal accommodation and the tangential momentum accommodation coefficients. The experimental results were compared to solutions of the Navier‐Stokes and Burnett equations as given by Schamberg and Lin and Street. The results of the Navier‐Stokes and the Burnett equations were found to approximate the density distributions well at Knudsen numbers below ∼ 0.05∼0.05 and ∼ 0.2∼0.2, respectively. At higher Knudsen numbers the analytical and experimental results differ considerably.