Abstract

Shock-related unsteadiness over axisymmetric spiked body configurations is experimentally investigated at a freestream supersonic Mach number of 2.0 at 0\(^\circ \) angle of attack. Three different forebody configurations mounted with a sharp spike-tip ranging from blunt to streamlined (flat-face, hemispherical, and elliptical) are considered. Steady and unsteady pressure measurements, short-exposure high-speed shadowgraphy, shock footprint analysis from \(x-t\) plots, and identification of dominant spatiotemporal modes through modal analysis are carried out to explain the unsteady flow physics. The present investigation tools are validated against the well-known events of ‘pulsation’ corresponding to the flat-face case. The hemispherical case is characterized by the formation of a separated free shear layer and associated localized shock oscillations. The cycle of charging and ejection of fluid mass from the recirculation zone is identified to drive the flow unsteadiness. Such an event triggers the movement of the separated and reattachment shocks in the opposite direction with respect to each other (out-of-phase shocks motion). In the elliptical case, the overall flow field resembles that of the hemispherical case, except with dampened unsteadiness. The value of the cone angle (\(\lambda \)) associated with the recirculation region is found responsible for the fluctuations caused by the charging and ejection of fluid mass. Thereby, it controls the extent of out-of-phase shocks motion. In the elliptical case, shock unsteadiness is reduced as \(\lambda \) is observed to be smaller. Based on the gathered results and understanding, the reduction in unsteadiness associated with the aerodisk mounted on the hemispherical forebody is demonstrated and explained via the almost complete elimination of the out-of-phase shocks motion.

Graphic abstract

中文翻译：

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超声速流动中轴对称尖峰体的与冲击有关的不稳定性

摘要

休克相关的过轴对称尖刺体配置晃动是在2.0的自由流超音速马赫数实验研究在0 \（^ \ CIRC \）的攻角。考虑了三种不同的前身构型，这些构型安装了尖锐的尖刺尖，从钝端到流线型（平面，半球形和椭圆形）。稳态和非稳态压力测量，短距离高速阴影成像，\（xt \）的冲击足迹分析绘制图，并通过模态分析确定主要的时空模态，以解释非定常流物理学。针对与平面情况相对应的众所周知的“脉动”事件，对本研究工具进行了验证。半球形情况的特征在于形成分离的自由剪切层和相关的局部冲击振荡。确定了从再循环区充入和排出流体的循环，以驱动流动不稳定。这样的事件会触发分离后的电击和重新连接的电击在彼此相反的方向上运动（异相电击运动）。在椭圆形情况下，除了具有不稳定的阻尼之外，整个流场类似于半球形情况。锥角值（发现与再循环区域相关的\（\ lambda \））是由流体质量的充注和喷射引起的波动所致。因此，它控制异相冲击运动的程度。在椭圆形的情况下，由于观察到\（\ lambda \）较小，冲击不稳定性降低了。根据收集到的结果和理解，通过几乎完全消除了异相冲击运动，可以证明和解释与安装在半球形前体上的航空器相关的不稳定性的降低。

图形摘要