超声速射流撞击凹面
Supersonic jet impingement on concave surfaces
AI总结：
本文通过数值模拟与理论分析，明确了超声速射流撞击凹面时螺旋与轴对称啸叫的不同频率选择机制，证实壁面曲率可有效控制啸叫振幅与表面载荷。
AI中文摘要：
本文采用可压缩大涡模拟、涡片建模与Powell反馈回路分析，研究了圆形超声速射流撞击凹面时的气动声学共振。壅塞射流工作在理想膨胀马赫数1.56、雷诺数6×10^4的工况下，考虑6种几何构型：2块L/D（L为喷嘴到壁面距离，D为喷嘴出口直径）分别为2.08和2.58的平板，以及4种固定深度、压痕展宽σ∈{0.4,0.8,1.6,4.0}的高斯凹面。随着压痕变窄，在L/D=2.6时，基音振幅较平板参考工况升高最多达23dB，同时壁面压力波动与力矩也增大。Powell-Tam源传递预算将该放大归因于马赫盘源振幅增加及上游反馈波更高效地返回喷嘴；更强的向上传播波与凹壁的声聚焦效应一致。对于螺旋模态，测得的频率与径向本征函数和涡片模型预测的引导射流模式吻合良好，支持其在闭合上游反馈路径中的作用；凹壁与平板的模式选择一致，说明该音调由等效理想膨胀射流的剪切层剖面而非壁面几何决定。相比之下，轴对称频率不与任何引导模态分支重合，而是遵循Powell经典回路长度准则。结果明确了螺旋与轴对称啸叫的不同频率选择机制，证明壁面曲率可有效控制啸叫振幅与表面载荷。
英文摘要：
The aeroacoustic resonance of round supersonic jets impinging on concave surfaces is investigated using compressible large-eddy simulations, vortex-sheet modelling, and Powell's feedback-loop analysis. The choked jets operate at an ideally expanded Mach number of $1.56$ and a Reynolds number of $6\times10^4$. Six geometries are considered: two flat plates at $L/D=2.08$ and $2.58$, where $L$ is the nozzle-to-wall distance and $D$ the nozzle exit diameter, and four Gaussian concave surfaces of fixed depth and indentation spread $σ\in\{0.4,0.8,1.6,4.0\}$. As the indentation narrows, the primary-tone amplitude increases by up to $23\,\mathrm{dB}$ relative to the flat-wall reference at $L/D=2.6$, together with larger wall-pressure fluctuations and moments. A Powell-Tam source-transfer budget attributes this amplification to increased Mach-disk source amplitude and more efficient return of the upstream feedback wave to the nozzle. The stronger upstream-propagating waves are consistent with acoustic focusing by the concave wall. For the helical cases, the measured frequencies and radial eigenfunctions agree closely with the guided jet mode predicted by the vortex-sheet model, supporting its role in closing the upstream feedback path. The same selection is recovered for concave and flat walls alike, so this tone is governed by the shear-layer profile of the equivalent ideally expanded jet rather than by the wall geometry. The axisymmetric frequencies, by contrast, coincide with no guided-mode branch and appear instead to follow Powell's classical loop-length criterion. The results identify distinct frequency-selection mechanisms for helical and axisymmetric screech and demonstrate that wall curvature provides effective control of screech amplitude and surface loading.
