To meet the high flow quality and low noise requirements of large aeroacoustic wind tunnels, more rigorous standards are necessary for the aerodynamic design of axial fans. Since low-noise fans typically employ a large number of blades, it is essential to consider the aerodynamic interference that occurs between adjacent blades during the design process. In order to prevent flow separation near the blade root, which is a phenomenon that can reduce efficiency and increase noise, this study abandons traditional isolated-blade free vortex methods as well as conventional free vortex cascade design approaches. Instead, an arbitrary vortex cascade design method is adopted, using a vortex exponent of $\alpha =0.85$. Blade row corrections are performed based on the charts provided by Wallis. This paper also summarizes the aerodynamic constraints and noise reduction strategies associated with the design of low-noise, high-efficiency axial fans. Through integrated optimization, a fan system is developed that combines rotor blades with counter-twisted stator vanes. The rotor consists of 16 blades with airfoils that are optimized for low Reynolds numbers, high lift, and favorable stall characteristics. The GOE797 airfoil (with a relative thickness of 16%) is used near the root, while the GOE796 airfoil (with a relative thickness of 12%) is applied at the tip. The stator includes 7 counter-twisted vanes that use the C4 airfoil, which has a relative thickness of 12%. At the design rotational speed of 310 r/min, the fan system achieves an overall efficiency of 86.2% and a blade tip speed of 119.7 m/s, which remains well below the 150 m/s limit defined for low-noise fans. Numerical simulations confirm that the fan operates stably, with an outflow direction that aligns with the tunnel axis and without any flow separation observed at the blade root within the full operating range. Experimental results further validate the design. The relative error between the calculated and measured flow rates, which are measured using the pressure difference method in the contraction section of the wind tunnel, is less than 2.3%. At different fan speeds, the maximum deviation between the measured and designed motor shaft power is 4.0%. At speeds above 100 r/min, all measured power values remain below the design limit. These results demonstrate that within the fan's operational speed range (which does not exceed 310 r/min), the wind tunnel achieves the target flow velocity and the motor shaft power output remains within the specified design limits.

This study numerically investigates the flow field and aerodynamic performance of the axial fan system in the 4 m × 3 m low-turbulent and aeroacoustic wind tunnel of Beihang University (BHAW). A hybrid CFD/ACTRAN approach is employed to evaluate the aerodynamic noise characteristics of the fan. The axial fan is designed using an arbitrary vortex blade row method with a vortex index of 0.85, calibrated with cascade data. The final configuration consists of 16 rotor blades and 7 counter-swirl stator vanes. The rotor uses GOE797 airfoils (16% relative thickness) at the root and GOE796 airfoils (12% relative thickness) at the tip, while the stator vanes uniformly adopt the C4 airfoil (12% relative thickness). Numerical results agree well with experimental measurements: at the design speed of 310 r/min, the deviation in flow rate is less than 2.3%, and motor power output deviation is below 4.6%. The simulated total pressure rise is 2364.9 Pa, showing a 3.4% deviation from the design value. Flow field analysis confirms well-preserved axial flow without separation across all operating conditions. Acoustic evaluation shows that at 310 r/min, corresponding to a maximum test-section speed of 80 m/s, the overall sound pressure levels measured at 10 m from the inlet and outlet are 124 dB and 123 dB, respectively. The discrete noise at the fundamental frequency of 82 Hz reaches 115 dB at the inlet and 113 dB at the outlet, meeting the low-noise design objectives.

To improve the measurement accuracy and reduce background noise in aerodynamic acoustic wind tunnels, this study focuses on the noise reduction design of the 4 m × 3 m fully acoustically lined, low-turbulence, low-noise large-scale aeroacoustic wind tunnel (BHAW) at Beihang University. It investigated noise reduction measures for the fan section, tunnel body, acoustic guide vanes, and collector section, with experimental validation conducted in the D5 aeroacoustic wind tunnel at Beihang University. Drawing on the DNW-LLF wind tunnel and findings from the D5 experiments, an acoustic treatment was developed for BHAW, ensuring minimal impact on turbulence intensity in the test section. The outer wall of the fan section was treated with micro-perforated panels and sound-absorbing foam (stainless steel micro-perforated panels with a 2% perforation rate and 600 mm thick sound-absorbing foam) to reduce fan rotational noise, particularly in the low-to-mid frequency range. Inside the tunnel, perforated panels combined with 200 mm thick sound-absorbing foam were used to attenuate mid-to-high frequency noise. To further reduce friction-induced noise in the first diffuser channel, a 3 mm thick acoustically transparent felt was applied over the perforated panels. The four corner guide vanes adopt a dual-arc configuration with double-sided acoustic treatment. In the collector section, a perforated panel with sound-absorbing foam was installed at an 8° contraction angle. Additionally, the exterior of the collector was wrapped with acoustically transparent felt to mitigate airflow impact noise. Wind tunnel measurements indicated that the turbulence intensity in the model region of the open test section ranged from 0.07% to 0.095% under various flow velocities, while in the closed test section it ranged from 0.041% to 0.046% (less than 0.05% for the design specification), meaning the turbulence intensity in the open section was approximately 1.7 to 2.1 times that of the closed section. At the design speed of 80 m/s, the far-field noise level of the open test section was measured to be between 74.0 and 74.4 dB(A) (less than 75 dB(A) for the design specification). Compared with the RTRI wind tunnel, the BHAW tunnel achieved approximately 7 dB noise reduction in the low-frequency range, exhibited comparable noise levels in the high-frequency range, and had an overall sound pressure level that was 0.6～1.0 dB lower than that of RTRI.

With the increasing depletion of fossil energy and increasing concern for environmental protection, propeller propulsion devices with high propulsion efficiency and low fuel consumption have received increasingly more attention than jet propulsion devices, ushering in new development opportunities. However, improving propulsion efficiency and reducing noise pollution have been major challenges in developing propeller aircraft. This paper thoroughly discusses the aerodynamics and aeroacoustics of the aviation propeller. At first, it summarizes the development history of propellers. Then, given the key aerodynamic problems, such as the aerodynamic characteristics of propellers and the propeller airfoils, the research status and the key progress are summarized and discussed from theoretical analyses, numerical calculations, wind tunnel experiments, and other research methods and techniques. Finally, the research achievements and the latest progress regarding the propeller aircraft aerodynamic noise at home and abroad are introduced, including the mechanism, prediction, and reduction of propeller noise; prospects for future research on aircraft propeller aerodynamics, noise, and optimization design are also presented.

Counter rotating propellers (CRPs) have recently attracted more attention due to their high thrust and aerodynamic efficiency. This article comprehensively reviews five aspects of coaxial CRPs: experimental research, aerodynamic performance evaluation, aerodynamic simulation, aeroacoustics prediction, and aerodynamic noise optimization design. Firstly, it summarizes the current domestic and international experimental achievements regarding the aerodynamics and aeroacoustics of CRPs. Next, it introduces the engineering methods for the aerodynamic force calculation of CRPs and elaborates on the strip theory developed by Lu Shijia Laboratory at Beihang University for the aerodynamic force evaluation of CRPs. Based on this, numerical simulation methods for CRPs are presented, and both frequency domain and time domain methods for predicting the aerodynamic noise of CRPs are discussed. Finally, it presents the current research achievements in the aerodynamic noise optimization design of CRPs.

This article aims to provide technical support for designing the large closed-loop aeroacoustics wind tunnel with low turbulence intensity and low background noise at Beihang University (BHAW). The effects of the corner guide vanes angle on the flow fields are analyzed for several different expansion ratios by numerical simulations with the k-ω SST turbulence model, and the optimal installation angle of guide vanes for the BHAW wind tunnel is determined. Numerical results reveal that the pressure loss coefficient decreases first and then increases with the augmentation of the installation angle of guide vanes at each corner expansion ratio. The results further indicate the existence of a minimum pressure loss coefficient, and the installation angle of the guide vanes corresponding to the minimum value has a positive correlation with the corner expansion ratio. With various expansion ratios, the local pressure loss initially decreases and then increases with the guide vanes installation angle. The results demonstrate that the maximum friction loss coefficient occurs at the middle of the guide plate for a given installation angle; the installation angle mildly affects the flow around the central guide vanes (guide vanes 6, 7, and 8). With the increase of the corner expansion ratio, the flow velocity uniformity at the corner outlet deteriorates, and the installation angle of the guide vanes with the best flow guiding effect increases. By minimizing the total pressure loss coefficient and velocity deflection angle at the pipeline outlet, BHAW adopted an installation angle of 44° for the first corner with an expansion ratio of 1.17, an installation angle of 44° for the second corner with an expansion ratio of 1, an installation angle of 43° for the third corner with an expansion ratio of 1, and an installation angle of 42.5° for the fourth corner with an expansion ratio of 1. Such a strategy results in the dynamic pressure coefficient in the core area of the wind tunnel test section being less than 0.2% and the horizontal velocity deflection angle being less than 0.1°, justifying the aerodynamic design of BHAW.