SUMMARYA framework is described and demonstrated for CFD analysis of helicopter rotors in hover and forward ight. Starting from the Navier-Stokes equations, the paper describes the periodic rotor blade motions required to trim the rotor in forward ight (blade apping, blade lead-lag and blade pitching) as well as the required mesh deformation. Throughout, the rotor blades are assumed to be rigid and the rotor to be fully articulated with separate hinges for each blade. The employed method allows for rotors with di erent numbers of blades and with various rotor hub layouts to be analysed. This method is then combined with a novel grid deformation strategy which preserves the quality of multi-block structured, body-ÿtted grids around the blades. The coupling of the CFD method with a rotor trimming approach is also described and implemented. The complete framework is validated for hovering and forward ying rotors and comparisons are made against available experimental data. Finally, suggestions for further development are put forward. For all cases, results were in good agreement with experiments and rapid convergence has been obtained. Comparisons between the present grid deformation method and transÿnite interpolation were made highlighting the advantages of the current approach.

SUMMARYThe study of rotor-fuselage interactional aerodynamics is central to the design and performance analysis of helicopters. However, regardless of its significance, rotor-fuselage aerodynamics has so far been addressed by very few authors. This is mainly due to the difficulties associated with both experimental and computational techniques when such complex configurations, rich in flow physics, are considered. In view of the above, the objective of this study is to develop computational tools suitable for rotor-fuselage engineering analysis based on computational fluid dynamics (CFD).To account for the relative motion between the fuselage and the rotor blades, the concept of sliding meshes is introduced. A sliding surface forms a boundary between a CFD mesh around the fuselage and a rotor-fixed CFD mesh which rotates to account for the movement of the rotor. The sliding surface allows communication between meshes. Meshes adjacent to the sliding surface do not necessarily have matching nodes or even the same number of cell faces. This poses a problem of interpolation, which should not introduce numerical artefacts in the solution and should have minimal effects on the overall solution quality. As an additional objective, the employed sliding mesh algorithms should have small CPU overhead. The sliding mesh methods developed for this work are demonstrated for both simple and complex cases with emphasis placed on the presentation of the inner workings of the developed algorithms.

Detached-Eddy Simulations (DES) of flows over clean and controlled cavities with and without doors are presented in this paper. Mach and Reynolds numbers (based on cavity length) were 0.85 and one million respectively. Spectral analyses showed that the DES computations were able to correctly predict the frequencies of the Rossiter modes for both uncontrolled and controlled cases. Flow visualisations revealed that the impact of the shear layer formed along the cavity on a slanted aft wall no longer creates a large source of acoustic noise. Therefore little acoustic propagation was seen up the cavity. This was confirmed by the analysis of the cavity wall forces, which showed that the oscillations of the shear layer were reduced when the wall was slanted. This aided in reducing the overall Sound Pressure Levels throughout the cavity and far-field. Comparisons of the flow-fields suggested that the addition of the doors also aided in stabilising the shear layer, which was also shown in the analysis of the wall forces. As a result, the addition of the doors was found to affect the clean cavity configuration significantly more than the controlled one.