Developments and challenges in rotorcraft aerodynamics

This paper is a review of rotorcraft Computational Fluid Dynamics (CID) in the light of the major unsolved problems, and some prospects and solution philosophy for solving them. A brief summary of unsolved problems concludes that the most important of these is that of predicting the rotor wake. This is because of the importance of the wake problem (for predicting acoustics, performance and vibrational loading) and because of continuing solution difficulties that ate related to grid size. Resolution of small scales (vortex core or viscous lengths) results in a grid whose size is impracticably large. An alternate approach is to explicitly enforce a core model (rather than accept an implicit model that results from the discretization of a chosen partial differential equation PDE and is subject to numerical dissipation). Examples of this enforced-model approach are “vortex embedding” and “vorticity confinement” and these are discussed in some detail. It is shown that these methods have the ability to represent both wakes and body surfaces and are a basis for a new type of model development. Until such methods are developed (and/or much more powerful computers and solvers become available) the working role of CFD must remain in the less grid-intensive applications, such as local blade-flow solvers coupled to comprehensive codes. Even for these local problems, much development is required.