Fundamental study of acoustic leakage through a gap between gasket and flange surface

Abstract

In this study, we theoretically and experimentally explore the acoustic leak of an entire acoustic system as well as the various gap occurring between a gasket and flange. We conducted the first-ever fundamental research related to sound transmission loss through a narrow gap between a gasket and flange. In the experiments, we constructed pipeline elements, including the gap and the leakage path, in the impedance measurement tube. In the theoretical analysis, we replaced the fluid path, including the gap, with acoustic elements that comprise an electrical equivalent circuit. We then conducted the analysis using the transfer matrix method. To calculate the attenuation of sound waves propagating through the gap, we considered friction in association with viscosity, primarily in the boundary layers of the inner wall, to derive the characteristic impedance and propagation constant. The trends between the calculated and the actual experimental values for transmission loss in the entire acoustic system coincided enough with regard to a large gap size range between 0.01 and 0.2 mm. Furthermore, the transmission loss linearly increased with the decreasing logarithm of gap for the calculated regions. Furthermore, the theoretical analysis and experimental results show agreement for incline gap conditions between the gasket and flange. The maximum gap also greatly affects the acoustic transmission loss for the inclined gaps. This was confirmed both by the experimental and the calculated values. We consider that these results provide fundamental acoustic knowledge specific to the narrow gap between the gasket and flange in an acoustic system.