Effect of Joint Distortions on Breakout Noise from a Flexible Rectangular Duct

Flexible rectangular ducts are widely used in Heating, Ventilating and Air Conditioning (HVAC) applications. These duct systems contain air handling units , which produce noise during their operation. This noise is transmitted through the ducts in both axial and transverse direction. This noise is transferred from the ducts to the surrounding atmosphere which is undesirable. The noise emitted depends on the structural properties of the duct as well as the acoustic properties of the medium. Current research work studies the structural dynamic properties of ducts and also the noise emitted from the ducts. Ducts with and without joints are used for the analysis, to study the effect of joints on dynamic response and noise emitted. Different structural parameters like natural frequency, mode shapes and duct surface vibration velocity are studied in both the cases to assess the effect of joints on dynamic response of the system. For analyzing the effect of joints on emitted noise, the parameters like duct transmission loss and radiation efficiency are studied. Both experimental and numerical approache s are employed in the study. In the current work, an analytical model is developed for the rectangular ducts to consider the effect of joints in estimating the modal parameters using free vibration analysis . The developed analytical model is validated by comparing the vibration responses obtained from experiments for a duct with joints. The effect of joints on the vibration response of the duct system is discussed based on the new analytical model