An Experimental Study of Aerodynamic Noise of the Wavy and Vibrissa Shaped Cylinders

Abstract

This paper presents an experimental study on the effectiveness of sinusoidal wavy-shaped and vibrissa-shaped cylinders as a passive control method on mitigating the aerodynamic noise of flow past a cylinder. A total of five differently-shaped cylinders with similar total volume, namely a circular cylinder with 22mm diameter, two sinusoidal wavy cylinders with different wavelengths (λ = 27.5mm and 55mm), one elliptical cylinder and one vibrissa-shaped cylinder, have been investigated in this study. Far-field noise measurements for all the cylinders have been performed at free-stream velocities from 8m/s to 35m/s. The results show that compared with the circular cylinder, wavy cylinders effectively achieve a overall noise reduction over a wide range of Strouhal number (0.1 < St < 2), especially prominent at the tonal peak of the vortex shedding frequency (i.e., St = 0.2). The result also shows that the smaller wavelength performs better than that of the larger. The elliptical cylinder results in slight noise reduction and a shift in the tonal peak frequencies. The vibrissa-shaped cylinder is the most effective among all, producing significant noise reduction over a wide St range albeit a small noise increase is observed at low Strouhal number of St < 0.12. To further understand the underlying noise reduction mechanism, time-resolved PIV measurements has also been carried out. Both the instantaneous and time-averaged velocity profile are compared with the baseline circular cylinder. The noise reduction in the wavy- and vibrissa-shaped cylinders is likely to be due to the modification and breakdown of the large-scale vortex shedding structures in the cylinder wake.