A free-wake methodology has been developed and applied to investigate the wake structures generated by twin-rotor systems, namely coaxial, tandem and side-by-side configurations. The basic formulation of the free-wake was based on a PIPC relaxation scheme (pseudo-implicit predictor-corrector) with five-point central differencing and velocity averaging in space. Although some empiricism, in the form of the vortex model and turbulent viscosity coefficient has been included in the formulation, these parameters were fixed and were not used to manipulate agreement between the computed ans measured wake geometries. While the free-wake methodology described here was originally developed for single isolated rotor analysis, it has been shown to be well suited for twin-rotor applications. The scheme has demonstrated good convergence characteristics and numerical stability, even for complicated rotor configurations such as tandem and coaxial systems, and under a wide variety of flight conditions. Efforts have also been made to validate the predictive capabilities of the present scheme by comparison with experimental data. While wake geometry data for the tandem and tilt-rotor configurations do not exist, predicted wake geometry boundaries for the Ka-32 coaxial rotor helicopter have been compared with experimental flight test measurements over a relatively wide range of advance ratios. In general, the predictions are in good agreement with the test data, and it is clear that the numerical wake model is able to capture the essential physics of the twin-rotor wake problem.
Free-wake analysis of tandem, tilt-rotor and coaxial rotor configurations
Freiwirbelanalyse von Tandem-, Kipp- und Koaxialrotorkonfigurationen
Journal of the American Helicopter Society ; 41 , 3 ; 196-207
1996
12 Seiten, 13 Bilder, 24 Quellen
Article (Journal)
English
Free-wake analysis of tandem, tilt-rotor and coaxial rotor configurations
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