AI 中文总结
本研究通过壁面解析大涡模拟，揭示了可压缩性对运输机后体尾流转捩的影响，发现45°上反角后体在马赫0.5时存在涡对到宽分离湍流尾流的迟滞现象，两种状态拓扑由马赫数历史决定。
AI 中文摘要
军用运输机后段采用大上反角的平面以容纳货舱门，其产生的流动特征会影响空投精度、伞兵安全及气动性能。基础研究主要聚焦于经典替代模型上的近不可压缩流动，该模型由与来流对齐的圆柱及带锋利边缘的平面上反后体组成。该流动呈现周向分离、马蹄涡，以及向下游持续存在的反向旋转流向涡对。本研究阐明了可压缩性对尾流的影响，并探究这些影响如何依赖于基部上反角。在名义雷诺数25000下，对32°和45°的上反角，分别以马赫数0.1、0.3和0.5开展了壁面解析大涡模拟。对于32°后体，马赫数增大使上游回流区扩大，并推迟涡对形成，而这些效应对下游的影响减弱。对于45°后体，类似的回流区增长在马赫0.5时触发分岔，从涡对状态转变为宽分离湍流尾流。马赫数降至0.3和0.1的序列显示出迟滞现象，即分离尾流状态在较低马赫数下持续存在，且对雷诺数变化具有鲁棒性。因此，在相同马赫数和雷诺数下，两种状态均可出现，其拓扑结构和压力载荷由马赫数的变化历史决定。
英文摘要
Aft sections of military cargo aircraft employ flat surfaces at high upsweep angles to accommodate ramp doors, producing flow features that affect cargo-drop accuracy, paratrooper safety, and aerodynamic performance. Fundamental studies have primarily examined near incompressible flow over a canonical surrogate consisting of a freestream aligned cylinder with a planar, sharp edged upswept base. The flow exhibits peripheral separation, a horseshoe vortex, and a counter-rotating streamwise vortex pair that persists downstream. The present investigation delineates the effects of compressibility on the wake and examines how these effects depend on basal upsweep angle. Wall-resolved large-eddy simulations are performed at Mach numbers of $0.1$, $0.3$, and $0.5$ for upsweep angles of $32^\circ$ and $45^\circ$ at a nominal Reynolds number of $25{,}000$. For the $32^\circ$ afterbody, increasing Mach number enlarges the upstream recirculation region and delays vortex-pair formation, while these effects diminish downstream. For the $45^\circ$ afterbody, similar recirculation-region growth triggers a bifurcation at Mach~0.5 from the vortex-pair state to a broad separated turbulent wake. A descending-Mach sequence to 0.3 and 0.1 reveals hysteresis, with the separated-wake state persisting at lower Mach numbers and remaining robust to Reynolds-number variation. Thus, both states can occur at identical Mach and Reynolds numbers, with topology and pressure loading governed by Mach number history.
