Sound radiation from the open end of pipes and ducts in the presence of mean flow

The radiation of sound from the open end of pipes and ducts is a common problem in environmental noise control. Examples include radiation from ductwork in heating, ventilation and air-conditioning systems, noise emissions from exhaust stacks in industrial power plants, as well as radiation from turbofan engines. These open duct terminations represent a relatively simple mechanical structure; however, the acoustics is significantly more complicated and this is especially true when a mean gas flow is present. This article presents an efficient numerical model suitable for analysing sound radiation from an unflanged duct termination, and introduces a method for including a uniform mean fluid flow in the exterior region away from the termination. An example of sound radiation from a turbofan engine is then investigated.