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本文根据S.E.Wright的BLH理论,导出了不等节距风机的声辐射公式,而等节距叶片风机声辐射公式是该公式的特殊情况。同时,从公式中可以看到不等节距叶片对风机通过频率及其谐波具有调制作用,这从理论上进一步阐明了不等节距叶片分布能降低噪声的原因。在公式中,还能预测出与等节距相比时叶片通过频率及其谐波所对应的噪声变化值,其计算值与试验值基本一致。试验表明,不等节距与等节距的相对变化率在较大范围内(本文推荐其变化率不超过20％)不会对风机气动性能产生大的影响,因此,可以灵活地选择叶片节距的最佳分布方式。
According to S.E. Wright’s BLH theory, the paper deduces the formula of sound radiation of variable-pitch fans, and the formula of sound radiation of constant-pitch blades is a special case of this formula. At the same time, it can be seen from the formula that unequal pitch blades have a modulating effect on the fan passing frequency and its harmonics, which theoretically further clarifies the reason why the unequal pitch blade distribution can reduce the noise. In the formula, it can also predict the change frequency of the blade through the frequency and its harmonic corresponding to the same pitch, the calculated value is basically consistent with the experimental value. Experiments show that the relative rate of change of unequal pitches and constant pitches within a relatively large range (in this paper, the recommended rate of change does not exceed 20%) will not have a big influence on the aerodynamic performance of fans. Therefore, the blade sections The best distribution of distance.