Noise reduction of sinusoidal wavy cylinder in subcritical flow regime

The sinusoidal wavy cylinder of circular cross section is able to substantially reduce the fluid forces by effectively stabilizing the near wake in the subcritical flow regime. Based on the anechoic wind tunnel measurements and large eddy simulations (LESs), we investigate the capability of the sinusoidal wavy cylinder to reduce aeroacoustic noise as well as underlying flow physics. The wavy cylinder studied in this work covers a range of spanwise wavelength λz = 1.8–6.0Dm and a range of wave amplitude a = 0.15–0.25Dm, where Dm is the mean diameter of the wavy cylinder. The wind tunnel measurements are conducted at Reynolds number ReDm = 2.9–8.0 × 104, while LESs are conducted at ReDm = 3.0 × 104. It is observed that the wavy cylinder's configuration, determined by λz and a, has a profound impact on the far-field sound pressure level (SPL) of both tonal and broadband noise. Compared with the baseline smooth cylinder, the wavy cylinder with λz = 1.8Dm and a = 0.25Dm can reduce the peak value of SPL at the tonal frequency by up to 36.7 dB. The reductions in the overall SPL of the tonal and broadband noise are also tremendous, by up to 31.0 and 7.5 dB, respectively, by the wavy cylinder with the optimum wavelength. Consistent with observations on noise reduction are the significantly weakened near-wake structures and largely attenuated spanwise coherence, as well as substantially suppressed pressure fluctuations in the near wake and over the cylinder surface, based on the LES results. Dependence of the noise reduction on Reynolds number is discussed as well.