Study of Vortex Noise of Rotating Blades

The paper gives a brief overview of propeller noise generation mechanisms. The vortex component of the propeller noise is considered in detail. The results of the study of the vortex noise of rotating rods in open areas are presented. The spectral, integral and spatial characteristics of the acoustic field of the rotating rods are obtained. We established that the audibility of rotating rods considered is determined by radiation in the frequency range 250--1250 Hz. We summarized the results of the studies regarding the effect of the flow around the blade profile, characterized by the Reynolds number, on the vortex noise intensity. Findings of research show that the exponent of the dependence of the vortex sound intensity on the characteristic velocity around the blade profile in various ranges of the Reynolds number can vary significantly. When changing the value of lg Re in the range from 1.8 to 5, the final dependence of growth rate exponent first falls from 6 to 3, remains equal to 3 in the range of lg Re from 2.65 to 3.2, and then again increases to 6 for lg Re in the range from 3.4 to 3.7, and with an even larger increase, the exponent increases from 7 to 8 and above (to 11) to lg Re = 4.5. At higher Reynolds numbers, (over 106) corresponding to self-similar modes of flow around the blades of light propeller aircraft, the exponent is 5. Based on the study, we recommend using one of the well-known trailing edge noise models for calculating the vortex noise of propellers at the sketch design stage. The paper also introduces the main methods formulated for reducing the intensity of the vortex sound of rotating blades

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