In this paper, a three-dimensional calculation model of a two-stage adjustable-blade axial-flow fan is established and verified by grid independence and numerical accuracy. The pressure distribution and sound power level distribution characteristics of the blade surface are explored with variable blade installation angles. Based on the Q-criterion, the study reveals the spatial distribution of the channel and trailing edge shedding and channel vortexes in the flow field. Then, the evolution laws of the fan's aerodynamic noise sound pressure level are also investigated, and its frequency domain characteristics with variable blade installation angles are obtained. The results show that when the rotor blade installation angle is -5{degree sign}, the front-guide vane matches the installation angle of the first-stage impeller. The upper limit of sound power level is the smallest with variable blade installation angles, which is 123.56 dB. Meanwhile, the number and size of vortex structures in the front-guide vane area are the smallest, and the turbulent flow in the flow field is moderate. As the moving blade installation angle is deflected from -10{degree sign} to 10{degree sign}, the total sound pressure level of aerodynamic noise at each component of the fan first decreases and then increases. The minimum value is 121.40 dB and 128.40 dB at the inlet and outlet when the blade installation angle is -5{degree sign}. In addition, the number of eddies periodically shed in the fan flow field is the least. This research can supply technical support for the noise reduction of the two-stage adjustable blade axial fan.
In order to research the structure-borne noise characteristics of a T-shaped tee considering fluid-structure interaction (FSI), the Large Eddy Simulation (LES) and acoustic Finite Element Methods (FEM) were used to simulate the flow field and structure-borne noise related to T-shaped tees under different inlet and outlet combinations. The results show that the frequency domain sound pressure level (SPL) distribution under various inlet flow velocities is stable, the structure-borne noise of the T-shaped tee is a high-frequency noise, and the SPL curves provide a peak distribution. Meanwhile, the distribution characteristics of the structure-borne noise in the frequency domain follows similar trends under different inlet flow velocities. Additionally, the structure-borne noise won't produce the mechanical resonance of the system. When the inlet velocity increases from 1 m/s to 3 m/s, the total sound pressure level (TSPL) increases from 83.71 dB to 98.18 dB, a relative increase of 17.3%. In addition, the frequency domain distributions of the SPL under various inlet and outlet combinations are basically similar. The TSPL of four inlet and outlet combinations for the structure-borne noise are III, IV, II, and I in descending order. When the inlet flow velocity is 1 m/s, 2 m/s, and 3 m/s, in the case of combination I, the TSPL of the structure-borne noise decreases by 6.28 dB, 5.59 dB, and 6.39 dB, in contrast to the combination III, respectively. This study provides the guidance for the noise control and structural optimization design of a T-shaped tee considering the FSI.
The so-called T-shaped reducing tees are typically used to divide, change and control (to a certain extent) the flow direction in pipe networks. In this study, the Ffowcs Williams-Hawkings (FW-H) equation and the Large Eddy Simulation (LES) methods are used to simulate the flow-induced noise related to T-shaped reducing tees under different inlet flow velocities and for different pipe diameter ratios. The results show that the maximum flow velocity, average flow velocity, and vorticity in the branch pipe increase gradually as the related diameter decreases. Strong vorticity and secondary flows are also observed in the branch pipe, and the associated violent pressure fluctuations are found to be the main sources of flow-induced noise. In particular, as the pipe diameter ratio decreases from 1 to 0.45, the Total Sound Pressure Level (TSPL) increases by 6.8, 6.26, and 7.43 dB for values of the inlet flow velocity of 1, 2, and 3 m/s, respectively. The distribution characteristics of the flow-induced noise in the frequency domain follow similar trends for different pipe diameter ratios.
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