Abstract
In order to clarify the relationship between the aerodynamic noise and the flow regime around the rotating blade of a propeller fan operated at the maximum efficiency point and the off-design point, the characteristics of fans with different solidity impellers were analyzed experimentally. At the off-design point, the broadband noise of the high solidity fan was much larger than that of the low solidity fan because the relative velocity increased according to the solidity and the noise sources increased because of the number of blades. In the case of the low solidity fan, the broadband noise due to wake vortex shedding was generated at the off-design point in the low flow rate domain and the maximum efficiency point because the relative flow around the blade separated easily.
Highlights
In the field of construction machinery, it is necessary to generate a large amount of artificial wind to cool the engine because the wind due to the traveling speed of an automobile is likely of little benefit to the machine
Whereas the relationship between the tip vortex and noise has been discussed in a study of the aerodynamic noise from the propeller fan [7], there are several reports stating that the affect of the tip vortex on the fan noise is small in the vicinity of the design point [8]
We find that because the relative velocity of P21 at the off-design point becomes much faster according to the solidity and the number of noise sources is increased because of the number of blades, these flow regimes of P21 are responsible for the higher broadband noise
Summary
In the field of construction machinery, it is necessary to generate a large amount of artificial wind to cool the engine because the wind due to the traveling speed of an automobile is likely of little benefit to the machine. It is necessary to analyze the mechanism of the aerodynamic noise at the realistic operation point that is generated from the maximum efficiency point and the off-design point in the low flow rate domain [2]. In a study on the aerodynamic noise of the propeller fan, the authors verified experimentally the mechanism of the discrete frequency noise of a propeller fan generated because of the pseudo rotor-stator interaction [4]. We focused on the wake vortex noise of the propeller fan driven at the maximum efficiency point and the off-design point, and sought to clarify the relationship between the flow regime around the rotating blade and the broadband noise. We mainly discuss the influence of the wake on the broadband noise of the fan
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