# Influence of Incident Shock on Fuel Mixing in Scramjet
## 4 Results and Discussion
### JET Flow Structure
The effects of these factors culminated in a substantially larger augmentation of boundary layer thickness in case 5 than observed in case 4. Interestingly, in case 4 and case 5, the boundary layer thickness varies most significantly at the z = 0.043 m plane, a phenomenon not observed in case 1 and case 2. This is because, in case 1 and case 2, far from the center jet, the bow shock intensity is low, diminishing its impact on the boundary layer thickness. However, at the z = 0.043 m plane,  
Figure 21: U = 1000 m/s iso-surface. cases 4 and 5 exhibit a significant thickening of the boundary layer due to the interaction of the bow shocks from the side jets with the bow shock of the central jet. This convergence intensifies the bow shock compared to cases 1 and 2, leading to an enhanced thickening of the boundary layer beyond what is observed in case 1 and case 2. Differing from case 4, there is also point C in case 5, where the boundary layer continues to thicken due to the interaction of the separation shock caused by the boundary layer separation on the lower wall after the injection with the upper wall. In case 4 and case 5, it was observed that an increase in boundary layer thickness or its separation exerted a compressive effect on the flow channel area, sufficient to induce the formation of shockwaves. There is a positive correlation between the extent of boundary layer thickening and the compressive effect of shockwaves: The thicker the boundary layer, the more pronounced the local compressive effect caused by the shockwaves. Particularly, at the z = 0.043 plane, the pressure increase exceeded that at the z = 0 plane, as demonstrated in Figure 22. This discrepancy can be attributed to the wall surface boundary layer at the z = 0.043 plane undergoing the maximum thickness variation. Additionally, the interaction between different shockwaves exacerbated the local compressive effects, subsequently leading to an elevation of pressure beyond the points of their intersection. In case 5, it was noted that the incident shock wave coincidentally acted at the intersection where the bow shock interacted with the separation shock generated from the upper wall surface. This interaction further intensified the shock compression effect, resulting in an elevated pressure behind the shock waves. The period of incident shock waves in case 5 caused the jet to be positioned within a local low-pressure area. Combined with the obstruction effect of the jet, this led to a relatively lower pressure region behind the jet. Additionally, the interaction region of the incident shock wave, bow shock, and the shock from the upper wall boundary layer in case 5 was closer to the lower wall than in case 4. This indicates higher pressure near the leading edge of the cavity in case 5. The high-pressure zone near the cavity, combined with the low-pressure area behind the jet, created an adverse pressure gradient. This induced the separation of the boundary layer at the leading edge of the cavity, as shown in Figure 23. Simultaneously, the separation shock wave caused by the boundary layer separation interacted with other shock waves, further exacerbating the pressure within the localized area, as demonstrated in Figure 22.  
Figure 17:0 Pressure distribution for different plans. In Figure 24, dashed lines A, B, and C indicated the positions of the jet, the leading edge of the cavity, and the trailing edge of the cavity, respectively. The pressure was observed to have risen sharply before reaching point A, a phenomenon that was primarily due to the obstructive effect of the jet. In cases 4 and 6, this pressure increase occurred earlier compared to case 5. This difference highlighted that the separation zone preceding the jet was more extensive in these two cases, thereby exerting a more significant influence on the pressure. Conversely, the average pressure within the cavity section in case 5 was found to be higher than in cases 4 and 6.