随着近些年来工程上总体布局的需要，等直隔离段在许多情况下已经无法适用，特别是当进气道与燃烧室之间存在空间错位时，必须使隔离段沿轴线进行弯曲。弯曲本身会带来一系列新的问题，例如压缩波、膨胀波、离心力等，其与隔离段内的激波串现象耦合后会使流场结构更加复杂。然而目前对于弯曲隔离段没有系统性的研究，相关工作也还处于起步阶段，因此有必要开展相关研究以对其内的流动特性和机理加深认识，从而为弯曲隔离段的工程设计提供支撑。

本文利用数值仿真方法对弯曲隔离段内的激波串特性及流动机理进行了研究，获得了反压作用下隔离段内的流态演变过程，考察了关键设计参数的影响规律，揭示了弯曲的内在作用机制，并初步探究了三维效应的影响方式。

首先，针对均匀来流条件下的二维弯曲隔离段流动开展了研究。结果表明，反压上升过程中存在交叉斜激波流态向单侧大分离流态的突然转变，且两种流态转变之间会出现迟滞。对此由下壁面附近连续压缩波形成的强逆压梯度发挥着主导作用，并且几何参数、来流马赫数变化导致的差异也均与此强逆压梯度有关。

其次，从非对称边界层和入射激波两个角度研究了非对称来流条件下二维弯曲隔离段内的流动特性，并结合进气道考察了隔离段弯曲对起动性能的影响。研究表明，受到隔离段进口非对称边界层的影响，汇聚压缩波会与增厚的下壁面边界层作用形成规模更大的分离区，使得下游反压更易前传，造成隔离段抗反压能力的下降。而一旦存在入射激波，其会替代汇聚压缩波成为决定流态的主导因素。在其作用下，下壁面附近会出现分离包，激波串跨越分离包时会有结构形态和位置的突变。入射激波不强时，激波串容易跨过分离包迅速到达管口处，但当入射激波较强时，下壁面接近管口处会出现强逆压梯度区，使得在较高的反压条件下激波串才能跨过此区域，最终导致隔离段的抗反压能力随入射激波增强先下降后上升。另外在进气道起动过程中，弯曲的膨胀效应则发挥了关键且正面的作用，使得隔离段弯曲角度越大时进气道的起动马赫数越低。

最后，针对圆形和矩形两种截面构型下的三维弯曲隔离段流动进行了研究。结果表明，弯曲造成的上下壁面压差会引发较强的涡旋，使下壁面附近低能流堆积，分离区规模显著扩大。对比圆截面与矩形截面弯曲隔离段可以发现，由于侧壁面和角区的影响，矩形隔离段流场结构更加复杂，畸变程度更严重。特别是当宽高比小于2时，侧壁对流动的不利影响更为显著。综合来看，在抗反压能力方面，圆截面弯曲隔离段与二维弯曲隔离段几乎相同，均优于有限宽高比的矩形截面弯曲隔离段。

In recent years, with the requirements of the overall arrangement of the engineering, the straight equal-area isolator is no longer applicable in many cases, especially when there is a spatial misalignment between the inlet and the combustion chamber, the isolator must be bent along the axis. Bending itself will bring a series of new problems, such as compression wave, expansion wave, centrifugal force, etc., which will make the flow field structure more complicated when coupled with the shock train phenomenon in the isolator. However, there is no systematic research on the curved isolator at present, and the related work is still in its infancy. Therefore, it is necessary to carry out relevant research to deepen the understanding of the flow characteristics and mechanism in the curved isolator, so as to provide support for the engineering design of the curved isolator.

In this paper, numerical simulation methods are used to study the shock train characteristics and flow mechanism in the curved isolator. The flow pattern evolution process in the isolator under the effect of back pressure is obtained. The influence law of the key design parameters is investigated. The internal effect mechanism of bending is revealed. And the influence mode of three-dimensional effect is preliminarily explored.

First of all, the study is carried out on the flow of two-dimensional curved isolator under the condition of uniform incoming flow. The results show that there is a sudden transition from the cross oblique shock wave flow pattern to the unilateral large separation flow pattern during the process of the back pressure rising, and there will be a hysteresis between the transition of two flow patterns. The strong adverse pressure gradient formed by the continuous compression wave near the lower wall plays a leading role, and the differences caused by the changes of geometric parameters and incoming flow Mach number are also related to this strong adverse pressure gradient.

Secondly, the flow characteristics in the two-dimensional curved isolator under asymmetric incoming flow conditions are studied from the perspectives of the asymmetric boundary layer and incident shock wave, and the influence of the bending of the isolator on the start performance is investigated in conjunction with the inlet. The results show that, under the influence of the asymmetric boundary layer at the entrance of the isolator, the convergent compression wave will interact with the thickened lower wall boundary layer to form a larger separation zone, making the downstream back pressure easier to transmit forward, resulting in the decline of the back pressure resistance capacity of the isolator. Once the incident shock wave exists, it will replace the convergent compression wave and become the dominant factor in determining the flow pattern. Under its effect, separated bubbles will appear near the lower wall, and there will be sudden changes in the structure and position when the shock train crosses the separated bubbles. When the incident shock wave is not strong, the shock train easily crosses the separation bubble and quickly reaches the entrance. However, when the incident shock wave is strong, a strong adverse pressure gradient region will appear near the entrance at the lower wall, so the shock train can cross this region only under high back pressure conditions, and eventually the back pressure resistance capacity of the isolator will decrease first and then increase as the incident shock wave intensifies. In addition, during the starting process of the inlet, the expansion effect of bending  plays a key and positive role, making the greater the bending angle of the isolator, the lower the start Mach number of the intake port.

Finally, the flow in the three-dimensional curved isolator with circular and rectangular cross-section configurations is studied. The results show that the pressure difference between the upper and lower walls caused by the bending will cause a strong vortex, which leads to the accumulation of low-energy flow near the lower wall, and significantly enlarges the size of the separation zone. By comparing the curved isolator with the circular section and the rectangular section, it can be found that the flow field structure of the rectangular isolator is more complex and the distortion is more serious due to the influence of side wall surface and corner area. Especially when the aspect ratio is less than 2, the adverse effect of the side wall on the flow is more significant. In general, in terms of back pressure resistance capacity, the curved isolator with circular cross-section is almost the same as the two-dimensional curved isolator, and both are better than the curved isolator with rectangular cross-section with finite aspect ratios.