EXPERIMENTAL-STUDY OF SUPERSONIC AXISYMMETRICAL BASE-FLOW

Supersonic flow from a circular convergent/divergent nozzle expanded suddenly into a circular parallel duct has been investigated experimentally. Attention was focused on the effects of nozzle exit Mach number, the ratio of enlarged duct to nozzle exit area and length to diameter ratio of the enlarged duct on the base pressure and mean wall static pressure field in the enlarged duct. The Mach number as wall as the area ratio have a significant effect on the base flow. The base pressure increases (the base drag decreases) with increasing approach Mach number. Also, the base pressure increases with increasing area ratio for all Mach numbers of the present study. It is found that the optimum length of the enlarged duct which gives the maximum base pressure at the tested Mach number and area ratio is equal to 6.0 times its diameter. The wall static pressure increases smoothly along the duct length in the case of supersonic flow compared to subsonic flow at the same geometrical conditions of the enlarged duct.