Design method of arbitrary vortex blade cascades for large-scale low-noise high-efficiency axial flow fans and its application in engineering aeroacoustic wind tunnels

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.