大型低噪声高效轴流风扇任意涡流叶栅设计方法及其在工程型声学风洞中的应用

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

  • 摘要: 大型气动声学风洞对试验段高流场品质与低背景噪声的需求,对轴流风扇的气动设计提出了更严峻的挑战。针对低噪声风扇桨叶片数多的特点,本文将桨叶之间的干涉行为纳入设计考量,同时,为避免桨叶根部区气流分离导致效率降低与噪声增大,放弃了传统孤立桨叶自由涡流设计方法和自由涡流叶栅设计方法,采用任意涡流叶栅设计方法,经过研究选取涡流指数α = 0.85作为设计值,并根据Wallis给出的图表和叶栅实验数据进行了桨叶叶栅的干扰修正。本文系统总结了低噪声高效轴流风扇的气动设计限制条件和降噪策略,并在此基础上开展了综合设计。最终设计方案采用桨叶和反扭导流片组合系统,风扇桨叶数目为16片,采用低雷诺数、高升力、失速性能良好的翼型,叶根区选用GOE797翼型(相对厚度16%),叶梢区选用GOE796翼型(相对厚度12%)。反扭导流片数目为7片,导流片翼型采用C4翼型(相对厚度12%)。在设计转速310 r/min下,风扇整体系统效率为86.2%,桨尖线速度为119.7 m/s,符合低噪声风扇桨尖速度不高于150 m/s的设计要求。数值模拟结果表明,风扇运行平稳,出口流动平行于风洞轴线,在工作转速范围内未见到桨根区气流分离。通过与实测数据进行比较,发现计算流量与实测流量(风洞收缩段压差法测量取得流量值)之间的相对误差小于2.3%;不同转速下电机输出轴功率的实测值与设计值相比最大误差为4.0%,且在转速大于100 r/min时,所有实测功率均未超过设计值。综合而言,本文设计的轴流风扇在不超过设计转速(310 r/min)时,可实现风洞速度目标,同时保证电机负载不超限,满足系统对气动性能与低噪声运行的双重要求。

     

    Abstract: 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.

     

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