Theoretical analysis of effects of boundary layer bleed on scramjet thrust

Abstract

The effects of boundary layer bleed on the scramjet thrust are studied in the present paper. A theoretical model is developed to evaluate the thrust increment and influencing factors. The thrust increment resulting from the bleed is dominated by the rise in total pressure recovery and bleed mass flow rate. The bleed mass flow rate exerts stronger impact on the engine thrust than the total pressure. According to current bleed design, it is a severe challenge for the engine to enhance its total pressure to maintain the original thrust when there is no bleeding. Furthermore, the initial total pressure recovery, fuel mass addition, combustion efficiency and area ratio of engine exit to entrance can affect the contributions of the bleeding to the thrust increment. The scramjet needs a higher rise in total pressure recovery to counteract the negative effect of bleed mass loss at higher initial total pressure recovery or larger area ratio of engine exit/entrance. More heat release results in a little lower demand on the rise in total pressure recovery for maintaining the scramjet thrust. These results will aid in understanding the fundamental mechanism of bleeding on engine thrust.