Abstract
The regions over which steady and unsteady rotor wake patterns exist have been examined numerically foroneand two-bladed rotors. A lifting-line theory is used to model each rotor blade, and a time-stepping vortex method is used to calculate the tip-vortex motion. Tip-vortex geometries for a rotor in hover and vertical climb have been computed.Thevelocitieswithinthee rstfewturnsofthewakehavebeenobtained,andtheresultsindicateaperiodic nature of the wake in both time and space. Temporal aperiodicity is observed beyond the e rst few turns of the tip vortex for hovering rotors, whereas forrotors in sufe cient climb the entire wakeissteady relative to the blades and both spatially and temporally periodic. Both Euler and Adams ‐Moulton schemes have been tested for accuracy. The numerical results are shown to be independent of both time step and spatial grid below clearly dee ned values. Rotor thrust calculations have been performed and the effect of the lower wake on rotor thrust determined. The computed thrust values show some variation because the lower wake remains unsteady. The results for the wake geometry are analyzed and compared to previous predictions and two distinct sets of experimental results.
Published Version
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