Gojon Romain, Parisot-Dupuis Hélène, Mellot Bertrand, Jardin Thierry
ISAE-SUPAERO, Université de Toulouse, Toulouse, France.
J Acoust Soc Am. 2023 Aug 1;154(2):1248-1260. doi: 10.1121/10.0020672.
The radiation characteristics of rotor-beam interaction noise are studied experimentally for low Reynolds number small-scale rotors in interaction with beams of different shapes, sizes, and downstream positions. The number of blades ranges from two to four. For the two-bladed rotor, the presence of the beam has no effect on the mean aerodynamic performance. Moreover, the blade passing frequency (BPF) and the high frequency broadband noise (BBN) appear not to be affected by the presence of the beam. On the contrary, the magnitude of the 2×BPF-25×BPF harmonics increases up to 30 dB compared to the case without beam, with an envelope consisting of two humps: one centered around 5×BPF and another around 20×BPF-25×BPF. For the first hump, a dipole-like pattern with minimal amplitude aligned with the beam can be observed, whereas another dipole-like pattern is observed for the higher frequency hump, but with a minimal amplitude over all the rotor disk plane. Compared to the two-bladed rotor, the presence of the beam has an effect on the mean aerodynamic performance of the three- and four-bladed rotors, increasing both the torque and the thrust at iso-rotational speed. This change leads to a change in the directivity of the BPF tone that decreases at a latitude angle of θ=0° and increases at a latitude angle of θ=40°. Moreover, the same two competing humps are observed on the BPF harmonics envelope. Interestingly, the frequency range over which an amplification of the harmonic magnitude is observed seems not to be influenced by the number of blades. Finally, the magnitude of the low frequency hump increases with the beam diameter, the rotational speed, and the number of blades but decreases with the rotor-beam distance. That of the high frequency hump increases also with the rotational speed and the number of blades, but not anymore with the beam diameter, and reaches a maximum value when the rotor-beam distance is at an intermediate distance of L = 25 mm. This hump is also influenced, to a lesser extent, by the shape of the beam. The two different evolutions permit us to conclude that the noise generation mechanisms leading to the two humps must be different. Scaling laws of the acoustical energy are derived for all those parameters. As already done for previous experiments without beam, all of the results are made available as an open database, at https://dataverse.isae-supaero.fr/.
针对低雷诺数小尺度转子与不同形状、尺寸及下游位置的梁相互作用时的转子 - 梁相互作用噪声的辐射特性进行了实验研究。叶片数量从两片到四片不等。对于双叶片转子，梁的存在对平均气动性能没有影响。此外，叶片通过频率（BPF）和高频宽带噪声（BBN）似乎不受梁的存在的影响。相反，与无梁情况相比，2×BPF - 25×BPF谐波的幅度增加了高达30 dB，其包络由两个峰值组成：一个以5×BPF为中心，另一个以20×BPF - 25×BPF为中心。对于第一个峰值，可以观察到一个与梁对齐的最小幅度的偶极子状图案，而对于较高频率的峰值也观察到另一个偶极子状图案，但在整个转子盘面内幅度最小。与双叶片转子相比，梁的存在对三叶片和四叶片转子的平均气动性能有影响，在等转速下增加了扭矩和推力。这种变化导致BPF音调的指向性发生变化，在纬度角θ = 0°时减小，在纬度角θ = 40°时增加。此外，在BPF谐波包络上观察到相同的两个相互竞争的峰值。有趣的是，观察到谐波幅度放大的频率范围似乎不受叶片数量的影响。最后，低频峰值的幅度随梁直径、转速和叶片数量增加，但随转子 - 梁距离减小。高频峰值的幅度也随转速和叶片数量增加，但不再随梁直径增加，并且当转子 - 梁距离为L = 25 mm的中间距离时达到最大值。这个峰值在较小程度上也受梁的形状影响。这两种不同的演变使我们得出结论，导致两个峰值的噪声产生机制必定不同。针对所有这些参数推导了声能的缩放定律。如同之前无梁实验所做的那样，所有结果都作为一个开放数据库在https://dataverse.isae-supaero.fr/上提供。
