Modelling sound radiation from an axial fan in a finite length duct

It is common for axial fans to be located in ducts of finite length and understanding the way in which sound radiates from this type of system is important in controlling noise emissions. However, this type of problem presents a significant computational challenge, especially if one is interested in understanding behaviour at higher frequencies where multiple modes propagate in the duct. This article presents a numerical approach for tackling this problem that is suitable for calculating the radiated sound field from a finite length duct using a series of point dipole sources to represent an axial fan located inside the duct. It is demonstrated that through the use of an efficient numerical approach it is possible to obtain predictions at frequencies that are high enough to reveal well know characteristics of finite length duct radiation, such as organ pipe modes.