Aeroacoustic Noise Generated by Air Flowing through a Slit in an HVAC System 2019-01-0891
Air flow issuing through a narrow slit sometimes generates noise. This phenomenon is identified as in some parts of automobile HVAC system.
The noise annoys drivers and passengers, which cause deterioration of the quality of an automobile.
In order to avoid such a flow noise, making the width of the slit wider or just sealing the gap is an available way. In HVAC system, however, the slit of the doors to control the mixing of hot and cold air, has a variety of range of opening, so that it is difficult to vary in width of the slit.
The noise is well known but the mechanism of the noise generation has not well been studied so far, especially from the point of the effect of the cavity existing around the slit. For air flow studies, Computational Fluid Dynamics has been a useful tool, but commercial CFD programs usually use a turbulence model such as RANS and the result of the flow behavior depends on the model selected in the calculation. In this study, Direct Numerical Simulation of the compressible subsonic flow without any turbulence model is adopted to investigate the flow issuing through a narrow slit and the noise generation mechanism. The numerical result shows how the unsteady distorted vortices created through the slit, and result in the noise emission. This study explains the process of the slit noise creation via the contribution of acoustic characteristics of the area after and before the slit.