开式冷却塔正常使用时，风机叶轮高速运转，风机叶片周期性运动，空气受到周期性的冲击，压力波以声速传播而产生噪声，噪声随风机叶片形状和尺寸的变化，噪声强度也会不同，若叶轮每秒钟的旋转速度为n(rps)当叶片数为Z时，其基频率fc由fc=n×Z决定，H为风机所提供压力，要求风机所提供压力越低即填料静压损失低，噪声则越低，叶轮圆周线速度越低，噪声就越低。

When the open cooling tower is in normal use, the fan impeller runs at high speed, the fan blade moves periodically, the air is impacted periodically, and the pressure wave propagates at the speed of sound. The noise intensity varies with the shape and size of the fan blade. If the rotation speed of the impeller per second is n (RPS), when the number of blades is Z, the basic frequency fc is determined by FC = n × Z, and H is the fan The lower the pressure provided by the fan, that is, the lower the static pressure loss of packing, the lower the noise. The lower the circumferential velocity of impeller, the lower the noise.

例如云凌冷却塔测定一台300型冷却塔，采用的风机全压为105Pa。根据轴流风机在平面叶栅中环量与流体总压的变化关系P=PZTN，流经过叶轮后，全压与空气密度，叶片数、每个叶型环量和叶轮每秒转数有关，当全压确定后，叶片数越多则可以降低风机转速，转速在保证风量、保证经叶片风压的前提下越低，噪声则越低。

For example, Yunling cooling tower measures a 300 type cooling tower, the total pressure of the fan used is 105Pa. According to the relationship between the circulation and the total fluid pressure of an axial-flow fan in a plane cascade, P = PZTN, after the flow passes through the impeller, the total pressure is related to the air density, the number of blades, the circulation of each blade type and the speed per second of the impeller. When the total pressure is determined, the more the number of blades, the lower the fan speed. The lower the speed is, the lower the noise will be.

风机噪声产生的另一个源头是空气压缩后排出以及叶轮高速旋转时因气体边界层分离而产生的涡流所引起的噪声，

Another source of fan noise is the noise caused by the vortex generated by the separation of gas boundary layer when the impeller rotates at high speed,

涡流噪声的频率：F=KV/D(HZ)

Frequency of eddy current noise: F = kV / D (Hz)

D----叶片在气体进口方向的宽度，

D -- width of blade in gas inlet direction,

V----叶片相对于气体的速度，

V -- speed of blade relative to gas,

K----常数0.15~0.22

K -- constant 0.15 ~ 0.22

叶片叶型弦长越短，风机叶端的速度越小，则涡流噪声越低。现采用的低静压填料，大气室、多叶片、低转速等方法来消除风机运转时所产生的不均匀冲击波及涡流噪声。

The shorter the chord length of blade profile is, the smaller the speed of fan blade end is, the lower the eddy current noise is. At present, the methods of low static pressure packing, atmosphere chamber, multi blade and low speed are used to eliminate the uneven impact and eddy noise generated by the fan operation.