Optimize the blade shape, material and number of blades of the fan to reduce fan rotation noise. The shape of the fan blade directly affects the eddy current intensity near the blade, so change the shape of the blade to make it more streamlined and suitable. The bending angle is beneficial to reduce the eddy current noise. The blade material of the fan also has a certain degree of influence on the noise.
Generally speaking, the larger the loss coefficient of the material, the smaller the noise. Increasing the number of blades of the fan can reduce the fan speed under the premise of obtaining the same air volume, thereby reducing the fan noise. However, when the number of blades is more than 6, increase the number of blades , the increase in air volume is limited, and it will also have a negative impact on noise reduction. When the circumferential speed of the fan blade reaches a certain level, the fluid at the tip of the blade will change from laminar flow to turbulent flow, resulting in sudden changes in noise and eddy current noise.
The generation of fan eddy current noise is not only related to the rotational speed, but also related to the relative position of each component in the cooling system and the engine installation. Generally speaking, the smaller the installation space, the higher the rotational speed, the easier it is to cause eddy current noise.
In order to avoid such noise, it should be done: the distance between the fan end face and the radiator core is 10-15% of the fan diameter, because the cooling capacity, flow and noise of the fan will vary with the distance between the fan and the radiator. Increase and increase, at a certain point increase to the maximum value and then gradually decrease with the increase of the distance. The fan is too far from the radiator core or too close to the backflow phenomenon. In addition, the fan should be far away from the engine, preferably 100mm The above, in order to reduce the eddy current noise, the radiated noise outside the machine is reduced by 2.5dB(A), and the noise reduction effect is very obvious. The use of sound-absorbing sponges has a very obvious effect on absorbing fan noise, mainly because in addition to the basic noise of lower frequencies, the fan also It has broadband characteristics, and the high-frequency components are very obvious. Especially when the fan airflow is high, the proportion of high-frequency noise is larger. The sound-absorbing sponge has a good effect on fan noise above 1000Hz, but its sound absorption coefficient should be greater than 0.5, and the sound absorption coefficient should be greater than 0.5. The larger the sound coefficient, the better the absorption effect.
Optimizing the design of a muffler with good performance is one of the important means to reduce exhaust noise. According to the muffler principle, the muffler has a resistive muffler, a resistive muffler, and an impedance composite muffler. The resistive muffler is based on The sudden change of the pipe section reflects part of the sound wave to the sound source, so that only the original part continues to propagate along the channel, so as to achieve the purpose of sound reduction. The resistive muffler uses sound absorbing materials to achieve sound reduction. When the sound wave is absorbed in the porous When propagating in the material, the sound-absorbing material will convert part of the sound energy into heat energy and dissipate, so as to achieve the purpose of sound reduction. The resistive composite muffler is a muffler that combines resistance and resistance. Sponge to achieve the purpose of noise reduction.
There are mainly the following methods to reduce the noise of the engine.
One is to strengthen the sealing of the engine compartment to prevent the transmission of engine noise;
The second is to thicken the cover to increase the sound insulation of the cover;
The third is to reduce the vibration of the engine by designing a better shock absorption system;
The fourth is to increase the rigidity of the engine casing and reduce the radiated noise of its local vibration.