THRUST LOSS DUE TO SUPERSONIC MIXING

The maximum thrust developed by a device in which two streams mix in a parallel configuration at supersonic velocities is estimated. Total p ressure profiles in a two-dimensional, compressible shear layer are ca lculated by assuming turbulent Prandtl and Lewis numbers of unity. As the convective Mach number M(c) rises, the total pressure acquires a d efect that becomes large for M(c) > 1. For sheer layers with equal fre estream total pressures, an analytical relation for the defect vs M(c) is found. The extent and magnitude of the defect agrees well with exp erimental data. The loss in total pressure is connected to the loss in thrust of a simplified model of a scramjet. The thrust loss is about 30% for M(c) = 2 and 50% for M(c) = 3. The trends are insensitive to d etails of the shear-layer velocity profile and to the ratios of freest ream quantities. The role of turbulent-energy dissipation in the reduc tion of total pressure is discussed.