There is a special field called aeroacoustics, which studies the related problems of fluid sound generation. At present, it is mainly used in airplanes. The acoustic gasket is installed in the inner wall of the external pipeline of the aircraft engine for noise reduction. The acoustic pad is probably a honeycomb compartment covered with perforated plates, which is several centimeters thick. If we want to apply this existing technology to the field of life, it will be too big. There is an urgent need for noise reduction in civil fields, such as notebook cooling fans, but noise is the last consideration in design, and noise reduction is too detailed to be quiet in users' minds. The measurement unit of noise is decibel (dB), which is directly proportional to the logarithmic value of sound pressure pulsation. If we want to reduce it by ~3dB, it is equivalent to halving the pressure pulsation. However, you don't feel much quieter. One of the most basic problems in aeroacoustics research is how to reduce the noise generated by fluid blowing on the wing (you can abstract all kinds of noise problems in your life into this basic problem yourself). The most intuitive answer is that the blowing wind is stable and the sound of wings is small; If there are no objects in the wind, there will be less noise. That's right ... the noise of turbulent wings is basically less than that of laminar flow (at the same flow rate), and the noise produced by turbulent flow is far less than that produced by fluid passing through objects at low flow rate, but how to reduce the noise? There is no standard engineering scheme. Therefore, if you want to reduce noise in your life, you must optimize the air duct. The more streamlined and beautiful the air duct looks, the less noise it will make. It is best to reduce the guide vanes (there is no object in the wind at this time). Or turn off the sound. Automobile development will also encounter aerodynamic noise problems, which are mainly reflected in two aspects: wind noise and wind vibration. Wind noise is the noise caused by the separation of A-pillar and rearview mirror when air flows over the body surface (this noise is mainly concentrated in several thousand hertz); Wind-induced vibration refers to the vibration of the cavity when the skylight and the side window are opened, and the airflow falls off at a fixed frequency at the window. At this time, low-frequency and high-intensity noise is generated (inaudible, but the ears are very uncomfortable).