Experimental study of the aerodynamic noise radiated by cylinders with different cross-sections and yaw angles

Abstract

Vortex shedding from cylinders has been extensively studied due to its occurrence in many engineering fields. Many experimental studies reported in the literature focus on the aerodynamics of the vortex shedding process but the literature about the radiated noise is more scarce. The aim of the work presented here is to extend the available noise data. Aero-acoustic wind tunnel tests were carried out using cylinders with different cross-sections: circular, square, rectangular and elliptical. Flow speeds between 20 and 50 m/s were used, corresponding to Reynolds numbers in the range from 1.6 × 10 4 to 1.2 × 10 5 . The dependence of the noise on the yaw angle, flow speed, cross-sectional shape, angle of attack and radiation angle (directivity) is assessed. The results obtained are compared, where possible, with those found in the literature for similar cases. It is intended that the results can be used for the validation and calibration of numerical and empirical aerodynamic noise prediction models.

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“…This can be chosen by adjusting the parameter a p2 . The bandwidth is defined here in terms of points 10 dB below the peak [22]. Hence, the value of a p2 is given by…”

“…(5) using experimental data found in the literature from measurements of Strouhal number, rms fluctuating lift coefficient and correlation length. The empirical constants of the normalised spectrum and the speed exponent are also determined using the experimental data presented in [22]. Table 1 shows the parameters used for the two reference cases to obtain the amplitude factor of the peak noise η p .…”

“…Table 2 shows the values of the empirical constants obtained for the peak noise of circular and square cylinders. The factor a p2 is selected to ensure that the bandwidth of the normalised spectrum matches the experimental data in [22]. These noise measurements were carried out in an open-jet anechoic wind tunnel using cylinders with different cross-sections.…”

“…The average value of the relative bandwidth for five flow speeds was B f / f 0 = 0.16 for the circular case and B f / f 0 = 0.28 for the square case. The value of the speed exponent α is also based on the results from [22]. Table 2: Values of the empirical constants used for the peak noise of the circular and square cylinders for use in narrow-band spectra.…”

“…To simplify the problem it is assumed that the variation of η b due to, for example the yaw angle, is related to the corresponding variation of the amplitude factor for the peak noise, η p . The ratio η p /η b is calculated from experimental results presented in [22,43]. Figure 4 (a) shows the difference between the overall sound pressure level (OASPL) of broadband and peak noise for five flow speeds and different cylinder cross-sections at a yaw angle of 0…”