Among the several noise-generation mechanisms of airfoil self-noise, trailing-edge bluntness noise is an important noise source, which is caused by the vortex shedding at blunt trailing edges. A numerical study on airfoil trailing-edge bluntness noise control using the bio-inspired wavy leading edges is presented in this paper. The high-fidelity, improved, delayed, detached eddy simulation (IDDES) method was used to calculate the flow field, and the acoustic analogy method was used for noise prediction. For both the blunt-trailing-edge airfoils, a baseline airfoil with a straight leading edge and a bio-inspired airfoil with a wavy leading edge were used in this study. The chord-based Reynolds number was 400,000, and there was no angle of attack. The numerical results show that the trailing-edge bluntness noise of the baseline airfoil was significantly reduced by the wavy leading edges. The sound pressure level reduction was about 3.7 dB at the characteristic frequency, and the maximum sound pressure level reduction was as high as 35 dB. The trailing-edge bluntness noise was decreased at all directional angles. The maximum overall sound pressure level reduction was 6.3 dB at 0°. In addition, by analyzing the pressure fluctuations, wake characteristics, turbulent vortex structures and spanwise correlation and coherence of the flow field, the noise-reduction mechanisms of the bio-inspired airfoil are deeply revealed.

This work presents numerical studies on the effect of wavy leading edges on airfoil instability tonal noise. Large eddy simulations are conducted for NACA0012 (National Advisory Committee for Aeronautics) airfoils with straight and wavy leading edges. The far-field aerodynamic noise is predicted using the Ffowcs Williams and Hawkings acoustic analogy theory. The inflow Mach number is approximately 0.17 with an angle of attack of 4.3°, and the chord based Reynolds number is 600 000. The present numerical method is first validated by existing numerical results and a semi-empirical model for the straight baseline airfoil. Then, the effects of wavy leading edges on the aerodynamic performance, aeroacoustic performance, and noise reduction mechanisms are discussed in detail. The wavy leading edge is found to be detrimental to the mean aerodynamic performance with a decreased lift and increased drag. However, the lift fluctuations are significantly reduced. The instability tonal noise and its harmonic are totally removed by the wavy leading edges, while an extra broadband hump appears at the middle frequency. The low frequency and high frequency noise are also increased by the wavy airfoil. The laminar separation bubble is removed, and the flow separation is decreased by the wavy airfoil in the vicinity of the trailing edge. The pressure fluctuations around the trailing-edge are considerably diminished, and the spanwise coherence spectra are also significantly reduced by the wavy airfoil. Furthermore, it is noteworthy that the coherence reduction spectrum at the source is almost consistent with the far-field noise reduction spectrum.

This paper presents numerical studies on the aerodynamic performance of a fan with porous-wavy leading edge. Different bionic treatments are modeled based on wavy leading-edge configuration and porous medium. The flow field is solved using the Reynolds-Averaged Navier–Stokes method. The numerical results show that the bionic configuration using a porous medium significantly reduces both the efficiency and total pressure ratio of the fan. Among these, the maximum reduction in the total pressure ratio is 0.0115, and the maximum reduction in the efficiency is 7.16%. The application of a porous medium leads to decreased blade loading, aggravated flow separation, and increased wake intensity and width, significantly impairing the fan's aerodynamic performance. An optimized design is implemented for the porous-wavy leading edge, and the effects of two parameters of the porous medium, porosity and mean particle diameter, on the aerodynamic performance of the fan are analyzed. The results show that the optimized porous-wavy leading edge reduces the pressure ratio by 0.0070 and decreases the efficiency by 3.12%. Furthermore, it is found that higher porosity and larger mean particle diameter improve efficiency. And the influence of porosity and mean particle diameter on the efficiency is correlated with the coverage ratio of the porous medium on the blades.

This paper presents numerical studies on the effects of upstream porous treatments on the hydrodynamic and hydroacoustic performances of a hydrofoil. The inflow velocity is 5 m/s and the chord-based Reynolds number is 2.5 × 10⁷. A rapid turbulent boundary layer (TBL) noise prediction method is proposed by coupling the Reynolds-averaged Navier–Stokes (RANS) flow simulations, the Lee’s empirical wall pressure spectrum (WPS) model and the Howe’s trailing-edge noise model. This hybrid model is well validated against the experimental data. Using the developed noise prediction method, the effects of upstream porous treatments on the hydrodynamic and hydroacoustic performances are systematically studied, focusing on key parameters such as porous coverage area, porosity, pore diameter and half-porous configurations. The results generally indicate that the porous treatments can significantly reduce the mid-to-high-frequency noise, whilst slightly increasing the low-frequency noise. Within this parametric range, a larger porous coverage area yields more pronounced mid-to-high frequency noise reduction. Specifically, when the porous coverage accounts for 10% of the chord length, the mid-to-high frequency noise reduction reaches 14.3 dB; as the coverage expands to 25% of the chord, the noise reduction in this frequency band further increases to 35.2 dB. While smaller porosity and pore diameter enhance noise reduction, they incur greater hydrodynamic penalties. Within the scope of this study, the minimum porosity (φ = 0.55) and the minimum pore diameter (d = 0.1 mm) achieved mid-to-high frequency noise reductions of 19.1% and 17.3%, respectively, while the drag coefficient increased by 8.9% and 17.3%, respectively. Furthermore, the noise reduction is found to deteriorate with increasing angles of attack (AOAs). The wall shear stress and boundary layer thickness are also significantly affected by the porous treatments. This work provides rapid evaluations and can also be used for the optimization of porous treatments.