EULER CALCULATIONS OF UNSTEADY INTERACTION OF ADVANCING ROTOR WITH A LINE VORTEX

The unsteady, three-dimensional flowfield of a helicopter rotor blade in forward night encountering a concentrated line vortex is calculated using an implicit, finite difference numerical procedure for the solu tion of Euler equations. A prescribed vortex method is adopted to pres erve the structure of the interacting vortex. The test cases considere d for computation correspond to the two-bladed model rotor experimenta l conditions of Caradonna et al. and consist of parallel and oblique i nteractions. Comparison of numerical results with the test data show g ood agreement for the surface pressures for both parallel and oblique interactions at subsonic and transonic flow conditions. The results in dicate that the subsonic parallel blade-vortex interaction is nearly t wo-dimensional-like and the unsteady time-lag effects appear to be neg ligible. However, both the three-dimensional and unsteady time-lag eff ects are found to be important under supercritical now conditions and these effects are accentuated in the presence of transonic shocks. In contrast, the oblique blade-vortex interaction is unsteady and three d imensional at both the subsonic and transonic now conditions.