Large axial fans are used for underground space. Since the noise level of the industrial blower is close to 120 decibel, it is necessary to install the silencers to reduce the high noise level
The Axial fan is a model with 100 horsepower and a flow rate of 3900 CMM, using FANDAS-Axial Code to predict the noise produced. Noise was also measured using the PULSE program and Microphone to measure the noise of the axial fans and compared the predicted noise and the measured noise.
In this thesis, two types of circular type pod silencers has been studied. Those correspond to circular type pod silencers with one-layer and two-layer. The present study considers circular type pod silencer with annular two-layered air-passages, and three design parameters of the silencer, pod diameter, air-passage gap and sound absorbing material thickness, are selected as free design variables of design optimization problem. The objective function of the present design optimization problem is defined as the overall pressure level at the outlet of silencer, which is determined through solving 3-D acoustic wave equation inside silencer by the ANSYS acoustic code, calculating TL(transmission loss) of silencer and finally subtracting TL from the measured fan noise spectrum. As optimization algorithm of the present study, PQRSM(progressive quadratic reponse surface modeling) method is applied to the silencer design problem with the design constraints for feasible ranges of the three free design variables.
Through the present design optimization process on silencer, respectively optimal design variables are found as the air-passage gap of 0.4 m, the sound absorbing material thickness of 0.25 m and the pod diameter of 1 m for silencer with one-layer, and air-passage gap of 0.2 m, the sound absorbing material thickness of 0.2 m and the pod diameter of 0.8 m for silencer with two-layer. respectively the noise attenuation by the optimal silencer, TL, is shown to be significant over the entire range of frequency and its overall pressure level reduction is 12 dB(A) for silencer with one-layer, and its overall pressure level reduction is 34 dB(A) for silencer with two-layer.