A new free-wake model has been developed to predict the tip vortex structure and flow-field velocities in a rotor wake. The model is based on a pseudo-implicit formulation with five-point central differencing in space, and is implemented as a two-step predictor-corrector relaxation scheme. The robustness of the scheme has been demonstrated for a wide range of advance ratios, from hover to moderately high speed forward flight. Computed tip vortex geometries and flow-field velocities have been compared to experimental results to demonstrate the predictive capabilities of the methodology. Since the present method is implemented as a predictor-corrector scheme, it requires about twice the computational effort per iteration compared to single-step explicit methods. The present scheme, however, is much more robust and much less susceptible to numerical instabilities than explicit type methods. Furthermore, the method has demonstrated very fast convergence, even at low advance ratios, as well as for relatively small spatial/temporal discretizations of the wake. The generalized discretization scheme used here also permits the use for unequal time and space step increments which may be useful for in several practical applications of the wake model, such as the use of adaptive strategies to accelerate wake convergence. Convergence trends were found to be relatively insensitive to the spatial/temporal discretizations chosen. Predicted wake geometries have also been compared to smoke flow and shadowgraph visualization results, and it has been demonstrated that the physics of the wake evolution are well captured by the current scheme. While some discrepancies exist between the computed and measured data, the differences are within the limits of experimental uncertainties. Comparisons between computed and measured flow field velocities have been shown to be in good overall agreement, although in some cases, the numerical method tends to underpredict the velocity magnitudes.
Rotor free-wake modeling using a pseudo-implicit technique - Including comparisons with experimental data
Modellierung der freien Wirbelströmung um ein Rotorblatt mit einer pseudo-impliziten Technik und Vergleich der Resultate mit experimentellen Daten
Journal of the American Helicopter Society ; 40 , 3 ; 29-41
1995
13 Seiten, 13 Bilder, 34 Quellen
Article (Journal)
English
A free-wake rotor analysis including ground effect
NTRS | 1987
|Rotor Free-Wake Modeling Using a Pseudoimplicit Relaxation Algorithm
Online Contents | 1995
|