Numerical simulation of aerodynamic noise characteristics of square-wave cylinder at Reynolds number 3900

Control of noise generated by flow around cylinders is of significant importance in various engineering applications. This paper analyzes the flow and acoustic fields of cylinders with square-wave profiles based on computational fluid dynamics, acoustic analogy, and vortex dynamics theory. To address noise reduction for cylinders, a hybrid aerodynamic noise numerical simulation method combining improved delayed detached eddy simulation with the Ffowcs Williams–Hawkings integral equation is employed. Refined numerical simulations of the flow characteristics, near-field sound sources, and far-field noise radiation characteristics of square-wave cylinders are conducted, elucidating the noise reduction mechanisms. The results indicate that square-wave cylinders contribute to reducing drag coefficient and effectively suppressing fluctuating lift coefficient, thereby significantly reducing overall noise. The optimal noise reduction performance for square-wave cylinders occurs at a crest-to-trough length ratio of 50%, achieving approximately 22 dB suppression of tonal noise at low frequencies and around 15 dB suppression of broad-spectrum noise at mid-to-high frequencies. Tonal noise is markedly suppressed or even eliminated. To explore potential noise suppression mechanisms, the study meticulously examines the deformation process of near-field vorticity around square-wave cylinders. The presence of square wave elongates vortex structures in the wake, suppressing the periodic shedding of cylinder vortices, altering lift coefficient fluctuation, pressure fluctuation fields, and changing the directivity of far-field noise radiation.