报告题目:
螺旋桨对轴对称湍流边界层的气动声学响应
Rotor aeroacoustic response to an axisymmetric turbulent boundary layer
报告嘉宾:周迪,加州理工学院博士后
报告时间:2023年11月28日9:00-11:30(北京时间)
报告形式:腾讯会议(172694077)
报告摘要:
本研究通过数值方法分析了安装在轴对称体尾部的五叶螺旋桨对轴对称湍流边界层的声学响应并解释了声音产生的物理机制。流经该轴对称体的流动其雷诺数为1.9×10^6,自由流马赫数为0.059。轴对称体鼻部和中段的湍流边界层通过壁面建模的大涡模拟计算,而在声学上重要的尾锥区域则采用了壁面解析的大涡模拟方法。螺旋桨的辐射声场通过Ffowcs Williams-Hawkings方程计算。在本研究考虑的两种螺旋桨前进比下,计算所得到的湍流统计量和声压频谱与弗吉尼亚理工学院的实验测量结果吻合良好。除了宽频湍流吸入噪音外,还捕获了接近桨叶通过频率倍数的谱峰和相伴的谷。研究表明,这些谱峰和谷是由桨叶连续切割同一相干结构产生的相互关联的非定常载荷偶极子源以及它们之间的构造性和破坏性干涉所致。在与螺旋桨相互作用前,这些相干结构在减速的尾锥边界层中迅速增长。研究还发现声辐射主要由桨叶外部区域主导,这是由于桨叶尺寸、来流湍流强度和桨叶运动速度在该区域较大导致。此外,本研究提出了一种混合自由流/对流马赫数的螺旋桨声压谱标度律,其能够较为准确地描述螺旋桨前进比对声压谱的影响。
The acoustic response of a five-bladed rotor to an axisymmetric turbulent boundary layer at the tail end of a body of revolution (BOR) is investigated numerically to elucidate the physical sources of acoustics, particularly the role of coherent structures in sound generation. The BOR is at length-based Reynolds number of 1.9×10^6 and free-stream Mach number of 0.059. Two rotor advance ratios, 1.44 and 1.13, are considered. The turbulent boundary layer on the nose and midsection of the BOR is computed using wall-modeled large-eddy simulation, whereas that in the acoustically important tail-cone section is wall-resolved. The radiated acoustic field is calculated using the Ffowcs Williams-Hawkings equation. The computed flow statistics and sound pressure spectra agree well with the experimental measurements at Virginia Tech. In addition to broadband turbulence-ingestion noise, spectral humps near multiples of the blade-passing frequency and accompanying valleys are captured. They are shown to be caused by correlated blade unsteady-loading dipole sources and their constructive and destructive interference as a result of successive blades cutting through the same coherent structures. The latter undergo a rapid growth in the decelerating tail-cone boundary layer before their interaction with the rotor. The acoustic radiation is dominated by the outer region of the blade due to a combination of larger blade chord-length, inflow turbulence intensity and blade speed. The numerical results also correctly predict the effect of the rotor advance ratio on the acoustic field. A mixed free-stream/convection Mach-number scaling successfully collapses the sound pressure spectra at the two advance ratios.
报告嘉宾简介: 周迪,2013年本科毕业于西北工业大学,2016年在北京航空航天大学获得硕士学位,之后于2022年在美国圣母大学获得航空航天与机械工程专业博士学位,现为加州理工学院航空航天系博士后,主要从事计算流体力学、湍流、气动声学等领域的研究。
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