In this paper, 3-D duct models of Continuous Positive Airway Pressure (CPAP) device are developed to investigate the internal airflow behaviours and to identify potential noise source locations. The Computational Aeroacoustics (CAA) with a hybrid approach is conducted in the ANSYS software environment. CFD simulations were used to investigate the internal flow behaviours of the duct systems. The predicted results have shown the internal flow characteristics as circulation and separation behaviours. Those behaviours were found at several locations such as 90-degree corners, restricted cross-sectional areas, etc. High levels of turbulent energy are also found in those locations indicated they are likely to have a high level of noise. Further investigation to predict the noise generated from the duct system to validate the findings in CFD simulations. The results showed that there is a high level of noise generated at the identified locations in the CFD simulations. The noise experiments were also conducted to compare with the predicted noise results. It was found the predicted models can be used to evaluate the flow behaviours inside the duct system.

In summary, the CAA with a hybrid approach is used to investigate the internal flow behaviours and the potential noise source locations of the duct systems in the studied CPAP device. The predicted results have explained and identified some potential noise source locations. These findings will be used as guidelines to optimize the internal flow and therefore improve the noise generated from ducts. The broadband noise source models are potential tools that can be used to determine the loudness at the source locations in the early product development process for reducing noise level and better sound quality as well as a cost-effective tool for noise prediction.

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