This figure, taken from Slater (2009), contrasts the difference between traditional and surface sonic mass flow coefficient data. The data used in both subfigures was obtained by Willis, Davis, and Hingst (1995) for a bleed hole angle of 90° relative to the local flow velocity.
The subfigure on the left plots the traditional sonic mass flow coefficient (Qsonic) as a function of the ratio of plenum static pressure (pplenum) to local boundary layer total pressure (pt plenum). It shows a decrease in Qsonic as the pressure ratio increases. The values for Qsonic are generally larger, indicating fewer losses, for flows with a lower local boundary layer edge Mach number.
The subfigure on the right plots the surface sonic mass flow coefficient (Qsonic-B) as a function of the ratio of plenum static pressure (pplenum) to local boundary surface static pressure (pB). It also shows a decrease in Qsonic-B as the pressure ratio increases. However, the values for Qsonic-B show only mild sensitivity to the local boundary layer edge Mach number, and can be represented by a single curve-fit.
Last updated 1 Apr 2016