Effects of incoming boundary layer on flow field characteristics and mixing performance of transverse jet in a scramjet combustor were numerically investigated by using Reynolds-averaged Navier-Stokes. Results indicate that there is a critical dynamic pressure ratio for every specific flow status. Only when the injection dynamic pressure ratio is less than that value

increasing incoming boundary layer thickness could effectively improve the jet penetration depth and mixing efficiency. Otherwise

variation of incoming boundary layer rarely affects the jet penetration depth and mixing efficiency. For the cases studied

the critical dynamic pressure ratio was around 0.900. At the same dynamic pressure ratio condition

the thick incoming boundary layer cases were only 0.93 times the total pressure recovery coefficient of the thin cases. The friction loss of imcoming boundary layer is the dominant factor affecting the total pressure recovery of the scramjet combustor

and variation of incoming boundary layer thickness makes little influence on total pressure recovery induced by the jet and its downstream flow field features.