Abstract
A numerical simulation method based on the Ffowcs-Williams and Hawkings model is employed to predict the mechanisms of the near-field aerodynamic noise distribution characteristics of an adjustable-blade axial-flow fan with different installation angles of moving blades (Δβ). The simulated results reveal that with Δβ changing from −12° to 12°, the changing curves of the maximum total sound pressure level (MTSPL) at the tip clearance region (A region), the leading edge region (B region), and the trailing edge region (C region) exhibit an apparently rising trend, which increase by 4.0 dB, 5.7 dB, and 4.3 dB, respectively. Besides, the MTSPL at the C region is always smaller than that at A and B regions within the studied installation angles. Additionally, the acoustic energy ratio (Cpi) is the ratio of the sound energy density of a certain frequency to the total sound energy density, which shows the various frequency distribution characteristics under studied angles. It is found that when Δβ deflects from −12° to 0°, Cp1 (the acoustic energy ratio at the low-frequency in the range of 20–500) decreases from 0.71 to 0.59, Cp2 (the acoustic energy ratio at the intermediate-frequency in the range of 500–2000) increases from 0.18 to 0.25, and Cp3 (the acoustic energy ratio at the high-frequency in the range of 2000–3000) rises from 0.1 to 0.16. This study derives the aerodynamic distribution characteristics of the TSPL and acoustic energy in the near field of moving blades, which reveals its changing rules and frequency distribution under various installation angles. The conclusions may provide guidance for the research regarding the technology of the noise control of the adjustable-blade axial-flow fan.
Highlights
At present, noise pollution is one of the four major pollutions in the world, and its solution is closely related to the living environment.1–3 The adjustable-blade axial-flow fan, one of the most important turbo-machinery components, has inherent merits, including the wide operating scope and high efficiency, and it has been extensively used to transport fluid by converting the mechanical energy to potential and kinetic energies.4 the noise within a wide frequency range is generated by various unsteady and complex flow phenomena when adjusting the installation angle.5,6 It has been realized that the noise generated by the axial-flow fan can deeply degrade the performance of the axial-flow fan and, more seriously, deteriorate the working environment and endanger the health of the surrounding residents
The variation curves of the total sound pressure level (TSPL) at the A region shown in Fig. 8 involve two parts, the first is Δβ changing from −12○ to −4○ and the second is Δβ deflecting from 0○ to 12○
The total sound pressure level (TSPL) and the frequency characteristics of the acoustic energy ratio (Cpi) of nearfield aerodynamic noise are proposed based on the numerical simulation model of an adjustable-blade axial-flow fan under different installation angles of moving blades
Summary
Noise pollution is one of the four major pollutions in the world, and its solution is closely related to the living environment. The adjustable-blade axial-flow fan, one of the most important turbo-machinery components, has inherent merits, including the wide operating scope and high efficiency, and it has been extensively used to transport fluid by converting the mechanical energy to potential and kinetic energies. the noise within a wide frequency range is generated by various unsteady and complex flow phenomena when adjusting the installation angle. It has been realized that the noise generated by the axial-flow fan can deeply degrade the performance of the axial-flow fan and, more seriously, deteriorate the working environment and endanger the health of the surrounding residents. It is of great importance to investigate the characteristics of the near-field aerodynamic noise inside the axial-flow fan under various installation angles of moving blades. The noise has gradually become an important indicator of axialflow fan performance, and it is of great significance on the development of high performance and low near-field aerodynamic noise of an adjustable-blade axial-flow fan. The simulated model of the adjustable-blade axial-flow fan based on the Ffowcs-Williams and Hawkings (FW–H) model is proposed to analyze the total sound pressure level (TSPL) and the acoustic energy ratio (Cpi) in the frequency domain of the near-field aerodynamic noise including the tip clearance region, leading edge region, and trailing edge region under varying installation angles. The relevant conclusions could lay the foundation for the investigation of the aerodynamic noise reduction technology
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