# Research on Computational Method of Supersonic Inlet/Isolator Internal Flow
## 1 Introduction  
As the main pressurizing components of the scramjet engine, the supersonic inlet/isolator has a vital influence on the overall performance, and the geometric throat section is usually used to divide the two. In the field of engineering, it is necessary to design a series of shock wave structures to decelerate and pressurize the high-speed incoming flow, gradually reducing the supersonic airflow at the entrance to subsonic for ramjets whose operating conditions are from Mach 2.5 to Mach 5.0, while the scramjet whose operating conditions are always higher than Mach 5.0, and its intlets are designed to provide supersonic airflow to the combustion process. For various flight conditions, it is necessary to ensure sufficient and stable airflow under the premise of not affecting the overall aerodynamic performance. The mixed compression supersonic inlet design is often used by ramjet/scramjet, which is mainly composed of two components: an external compression part and an internal compression part. Due to the SWTBLI, shock wave/expansion wave interaction and some other factors inside the inlet/isolator, the flow state is extremely complicated. So far, plenty of studies have been carried out on the supersonic inlet/isolator, which are mainly divided into two categories: experimental research and numerical research. The experimental research in this field is more demanding on equipment requirements,which makes operation and the guarantee of accuracy difficult. [PERSON] et al. [1; 2] conducted an experimental study on a two-dimensional supersonic inlet/isolator. Both the length of the isolator and the outlet back pressure were adjusted to observe the changes in the isolator. By controlling the throttling degree at the outlet of the isolator to simulate the application of back pressure, it is found that an increase in the length of the isolator can reduce the pressure sensitivity of the inlet. [PERSON] et al. [3], and NASA Langley Research Center [4] have also conducted series of experimental tests to study the effects of different geometric parameters and flow control technologies on the overall performance of supersonic inlet. These experiments allowed researchers to explore influence factors of the inlet's start/unstart phenomenon and better understand the underlying physical mechanisms. However, it is hard to get more details of the flow fields inside the inlet/isolator so as to further optimize the corresponding structures [5], and then many research teams tried to study the inlet numerically. With the development of computer performance, an increasing number of scholars have chosen to use numerical simulation to predict the performance of the supersonic inlet/isolator under different operating conditions. At present, the RANS-based CFD solver is widely used in industry. NASA had proposed in 2010 that RANS would be continuously and extensively used in the next 20-50 years [6]. [PERSON] et al. [7] and [PERSON] et al. [8] used the commercial CFD solver ANSYS Fluent to study the shock train movements inside the supersonic inlet caused by the back pressure on the outlet boundary. [PERSON] et al. [9] completed a 3D flow simulation of a two-dimensional supersonic inlet/isolator based on CFD++ (mainly studying the starting performance), which indicated the turbulence models can greatly affect the computational performance of the inlet and the subtle differences between 2D and 3D computations have also been compared. [PERSON] et al. [10] used ANSYS Fluent to simulate the effect of ejecting flow on the supersonic inlet/isolator performance of resisting the back pressure, and revealed the mechanism: the ejecting increases the mixing of momentum, mass and energy to narrow the subsonic band and suppress the adverse pressure gradient. Since 2009, CFD research has gradually started to use DES or LES to perform simulations of the supersonic inlet/isolator so as to obtain a more refined flow field structure and spatiotemporal correlation of turbulence. [PERSON] et al.