Micro-shock tube flow behavior at low Mach number

Navier-Stokes computations are used to study the shock wave and contact surface propagation and the evolution of the distance between them (named hot flow length) in laminar flows in micro-shock tubes. These numerical results are compared with previous analytical results. In contrast to usual macroscopic shock tubes, the hot flow length and the contact surface propagation may have a different behavior due to the strong viscous effect of the wall boundary layer. For a low Mach number (M-s,M-i = 1.3) in a tube with a hydraulic diameter equal to 200 mu m, the numerical results show that two flow regimes take place behind the shock wave when its intensity decreases along the capillary tube. The first one is similar to the well-known coupled boundary layer/core flow regime and the second one occurs when the boundary layer completely fills the tube section. In this last configuration, the contact surface velocity strongly decreases due to a propagation in a fully developed viscous flow and leads to a re-increase of the hot flow length along the tube.