Aerodynamic noise characteristics of the flow past a circular cylinder

The present study experimentally investigates the aerodynamic noise from the flow past a fixed circular cylinder. The cylinders considered for the study have the diameters (d) in the range of 6 to 25 mm while its span length (L) is constant, which is 300 mm. The free stream velocity is varied up to 50 m/s, and the corresponding Reynolds number (based on d) varies up to 8.3 104, thus maintaining the flow past the cylinder in the subcritical regime. The discrete narrowband frequency tones depicting the aeolian tones are noted in the spectra. The results showed that the aeolian tone frequency decreases with an increase in the cylinder diameter and ceases to exist beyond the diameter of 15 mm. The corresponding Strouhal number of these tones is found to be in the range of 0.18 to 0.21, which is in congruence with the vortex shedding frequency in the subcritical regime. The maximum overall sound pressure level for cylinders having tonal noise is higher by around 30 dB compared to the background noise. Directivity studies show that the noise level is higher along the perpendicular direction of the jet flow. A sixth power Mach number scaling of the acoustic spectra shows a good collapse of the acoustic tonal amplitude.