In a constant-cross-confined-space with rearward facing steps

the skin-friction drag and drag reduction technics in a supersonic inner flow path was developed by three-dimensional numerical simulation. The influential mechanism of skin-friction drag in the same mass hydrogen injection and combustion but under different air inlet conditions and combustor entry conditions when the scramjet engine operated from flight Mach number 5

6

6.5 and 7

and different injecting pressure effects on the wall shear stress beheading the injectors were analyzed and compared. The results show that the drag reduction effect under low injection speed is more obvious than that under high injection speed. 507 kPa obtains 10% drag reduction and 50.7 kPa obtains 5%. Boundary layer combustion achieves almost 70% drag reduction. When the fluid passes backward facing step

regularly uneven changes of wall shear stress will appear and the biggest difference is 100%. The trends of wall shear stress and density are basically the same. Therefore

the key point of skin-friction drag reduction in inner flow path is building low density field near the wall surface. The area with stable and effective drag reduction effect is located more backwards of the injectors. However

due to the mixing and consumption of fuel

the drag reduction effect gradually decreases along the flow direction.