## 3 Results and Discussion
### Effect of Compression Direction on Overall Performance of Inlet  
In hypersonic vehicle design, the compression direction of the inlet significantly affects internal airflow characteristics and total pressure recovery, particularly as the airflow interacts with the vehicle body. To simulate the inlet mounted on the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mesh Scale** & **Cell Count (Million)** & \(\sigma_{inlet}\) & \(\phi\) \\ \hline Coarse & 0.46 & 0.5071 & 0.8563 \\ Medium & 1.03 & 0.5442 & 0.8831 \\ Fine & 2.11 & 0.5483 & 0.8903 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Grid dependence comparison. Figure 6: Surface pressure distributions along the bottom wall. positioned at \(\mathrm{L}/\mathrm{H}=12\). The design parameters for the 2D inlet mentioned are a height H of 100 mm, a half-width W\({}_{2}\) of 100 mm, and a compression angle of 12\({}^{\circ}\). In this paper, two compression directions are chosen. They are normal and inverted layouts, respectively. Normal layouts typically direct airflow away from the vehicle body upon compression, while inverted layouts bring the compressed airflow closer to the body. For specific comparisons of the external designs of both layouts, please refer to the accompanying Figure 7. Through numerical simulation and comparative analysis, significant differences in inlet performance between normal and inverted layouts emerged. Specifically, the inverted layout exhibited an approximately 8.24% increase in flow coefficient \(\phi\) compared to the normal layout. However, it is worth noting that the inverted layout demonstrated inferior total pressure recovery \(\sigma_{inlet}\) performance, with a reduction of 11.46% compared to the normal layout. Table 2 provides a detailed description. Therefore, a comprehensive consideration of the balance between flow coefficient rate and total pressure recovery is crucial in determining the inlet compression direction during the design process. An in-depth study of the symmetry plane contours in Figure 8 reveals significant differences in the flow field structure between the inverted and normal layouts. Specifically, the streamlines in the direction of airflow compression vary between the two layouts: In the normal inlet layout, the streamlines noticeably incline towards the fuselage side. Additionally, the forms of incident shocks differ significantly between these two inlet configurations. In the normal inlet layout, low-energy flow tends to enter the external compression ramp. Due to the outward shift of the equivalent wall formed by the boundary layer, the incident shock generated in the external compression ramp also shifts outward, away from the lip, which may lead to flow spillage and affect inlet performance. In contrast, in the inverted layout, the boundary layer resides on the fuselage side, keeping the external compression ramp unaffected. This allows the oblique shock to maintain a stable shape, effectively eliminating spillage issues, thereby enabling the inlet to more efficiently capture and guide airflow. The compression surface in the normal inlet layout is covered by the boundary layer, resulting in a lower airflow Mach number sensed by the compression surface compared to the actual incoming Mach number. Typically, for the same inlet, the lower the incoming Mach number, the higher the total pressure recovery coefficient. This phenomenon is particularly pronounced in the normal inlet layout and requires careful consideration in the design process. It is also observed that streamlines originating from the same distant position are captured within the inlet in the inverted intake layout, whereas they overflow from the lip in the normal inlet layout. This results in a lower flow rate for the normal inlet layout compared to the inverted inlet layout.