The purpose of this paper is to describe the current status of open rotor noise prediction methods and to highlight future challenges in this area. A number of analytic and numerical methods are described which can be used for predicting 'isolated' and 'installed' open rotor tonal noise. Broadband noise prediction methods are also described and it is noted that further development and validation of the current models is required. The paper concludes with a discussion of the analytical methods which are used to assess the acoustic data collected during the high-speed wind-tunnel testing of a model scale advanced open rotor rig.
IntroductIonThe advanced open rotor offers potentially significant reductions in fuel burn relative to current generation turbo-fan engines. Because of this significant benefit, the open rotor is currently being investigated by a number of leading aeronautical companies as a potential aircraft propulsor. A cut-away view of an open rotor concept is shown in Fig. 1 below. The engine consists of two contra-rotating rotors which, in this case, are driven by a gas turbine engine housed within a large centrebody which protrudes both fore and aft of the rotors. In order to be a viable aircraft engine, the open rotor will need to meet stringent noise certification standards and thus, a range of prediction methods are required for assessing the noise produced by various open rotor designs. These range from simple analytical methods, which are useful for design optimisation studies e.g. Parry and Vianello (1) , to high-fidelity CFD/CAA methods which are useful for design validation e.g. Colin et al. (2) . The purpose of this paper is to describe a range of noise prediction methods and, in particular, to highlight recent developments and to identify further work which is required.