# Research on Computational Method of Supersonic Inlet/Isolator Internal Flow
## 4 Inlet/Isolator Simulations
### Results and Analysis  
#### 4.3.1 Results--RANS  
(1) 2D Computation  
a. Reconstruction: 3 rd MUSCL Scheme  
[PERSON] [1] mentioned that, for the flow at the central section of the two-dimensional inlet/isolator, the 3D effects of the side wall can be ignored. So, in this part, a 2D simulation based on RANS is performed. In order to complete the grid independence verification, this paper solves three sets of meshes with different sparsity, as mentioned in the last section \"Mesh and Boundary Conditions\", by using the compressible RANS-based CFD solver developed: combine the 3 rd-order MUSCL reconstruction scheme, the AUSM flux computation scheme, the \(k-\omega\) SST turbulence model and the LU-SGS steady-state time integration approach. The simulation results of different meshes mentioned in Table 1 are shown in Figure 7: all the results are in good agreement with the experimental test, and the simulation outcomes of the medium and fine mesh are almost the same, with only slight differences, so in the subsequent computations, the medium mesh is adopted. Figure 5: Mesh of the 3D computational domain. Figure 6: Mesh of the quasi-3D computational domain. It can be seen from Figure 8 that the wave system inside the intake duct is highly complicated. The oblique shocks are reflected multiple times inside the isolator, and there are strong interactions of shock waves/expansion waves and shock waves/turbulent boundary layers, leading to obvious flow separations near the throat of the inlet. By the comparison of Figure 8, the shocked flow field structure obtained through numerical simulation is basically consistent with the experimental test results, and the pressure distribution is also roughly the same as the test of Figure 7. However, there are some small deviations between them: it can be seen from Figures 7 and 8 that, in the rear part of the isolator, the simulation results show that the oblique shock incident point is slightly farther back, and comparing the experimental Schlieren picture and the computation results, it can be found that the simulation's boundary layers are thinner and the separation near the throat is smaller. schemes is more similar to the experimental Schlieren picture. As a result, for a steady-state calculation, the flow fields obtained from the low-order reconstruction schemes can be treated as the initial conditions for the higher order schemes. By comparing the results of this paper with those of other research teams [1; 7; 31; 32; 10] (most of them are based on ANSYS Fluent, and have partly used in-house CFD solvers), as shown in Figure 11, we verify the computation accuracy of the CFD solver developed in this paper, and also find that the partial deviations between the simulation and experiment are common problems of the 2D RANS computation--the RANS accuracy is limited. Figure 10: 5 th WENO simulation results. Figure 9: Comparison of simulation results for the three reconstruction schemes. (2) 3D Computation  
The 2D computation of the inlet/isolator is a simplified ideal case. In reality, the 3D effects of the side wall may cause unsstart under some extreme conditions. Therefore, a 3D computation is performed to compare the 2D/3D simulation results based on RANS. The generation of 3D computation's mesh is based on the 2D medium mesh, and it is divided into 100 layers in the thickness direction, which are also refined near the side wall, ensuring the \(Y^{+}\) of the first layer equals to 1. As shown in Figure 12, there is a strong rolled-up lateral flow near the sidewall of the inlet throat, which also interacts with the separation area at the ramp, and the flow inside the separation bubble is relatively disordered: the flow distribution in the Z direction is extremely uneven, and the 3D effects are quite obvious. Through Figure 13, it can be seen more intuitively that the 3D computation results are closer to the experimental test, which are all extracted from the central plane in Z direction. Figure 11: Comparison of other researchers’ results based on RANS.