The relationship between the rotational speed of the tunnel fan and the air volume
The air volume of a tunnel fan reflects its ventilation and cooling capacity. We understand the relationship between the rotation of the tunnel fan and the air volume: during operation, the rotation of the fan blades alters the type and quantity of airflow as well as its velocity.
We can experiment by adjusting the rotational speeds of two tunnel fans—the low-pressure fan and another fan—with pressure installed at the exhaust outlet, and operating both fans under identical conditions to observe air volume. The rotation speed of tunnel fans is not a decisive factor; the primary determinants of air flow rate are inherently interrelated.
The undeniable proportional relationship between the air velocity and operational speed of tunnel fans is well-established; knowledge and control of these factors are directly correlated with increased air flow rates in tunnel fans. Controlling the air volume of tunnel fans is a prerequisite condition.
Methods for reducing noise: Analysis indicates that the primary source of fan noise is dipole sources. The total noise level of a tunnel fan is six times its rotational speed. Furthermore, it can be inferred that the noise originates from the effect of blade motion on air pulsation forces. The fan can be considered to have two low-frequency noise sources: the pressure field generated by blade movement and the dynamic pulsation noise caused by blade motion; the distance between stationary and moving blades in pneumatic tires is a significant factor contributing to interference noise.
The blades can also serve as acoustic barriers to enhance the acoustic radiation generated by lifting pulses over long distances. The effectiveness of this effect depends on the ratio between the wavelength associated with the lifting pulse and the size of the blade used for pulsation. The variation in radiation intensity described in Chapter 2 of Barrie represents a significant change across a frequency range exceeding 1 Hz. This effect is particularly pronounced when both upstream and downstream of the noise-emitting blade, with an equal number of blades in each row, collide simultaneously with the noise-emitting blade. Rotor blades can effectively create acoustic barriers on either side of the sound source.
As the distance between stationary and moving plates increases, the impact of current interference becomes significantly more pronounced than that of wake flow velocity. The effect of blades as acoustic barriers diminishes over time. At least three parameters influence interference noise: the waveform of the velocity field, the alignment distance between blades, and the radiation surface area of the blades. Short distances can produce two distinct acoustic effects: if the force pulse generated by the stator’s interference field causes the rotor to act as an acoustic source, then the stator functions as an acoustic barrier.