Analysis of Choked Viscous Flows through a Constant Area Duct

Abstract

The phenomenon of choked flow has been recognized and understood for many decades. These flows also have a variety of practical applications, such as pneumatic systems, oil and gas well blowouts, and vents in high-pressure systems, among others. According to some recent experiment data carried out in a straight pipe, the flow Mach number exceeds unity at the exit of pipe. This conflicts the Fanno flow theory that has long been applied to the one-dimensional gas dynamics area. At present, it is not clear whether this comes from experimental errors or any other reasoning that was not yet disclosed. There may be a suspected possibility of boundary layer thinning near the duct exit, which accounts for a divergent flow passage. The main objective of the present effort is to understand the flow mechanism by which the main flow Mach number exceeds unity near the exit of a straight duct. Both computational and theoretical analyses have been performed to investigate the detailed choking phenomenon at the vicinity of duct exit. The results obtained show that boundary layer thinning is produced by the flow at the vicinity of duct exit, with subsonic inlet conditions, consequently leading to the divergent flow passage. The sonic conductance is analysed in terms of pressure loss and boundary layer blockage with different duct sizes.

Keywords

compressible flow boundary layer internal flow choking sonic conductance

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