A VORTEX EMBEDDING METHOD FOR THE COMPUTATION OF HELICOPTER ROTOR FLOWS INCLUDING CLOSE BLADE - VORTEX INTERACTIONS

THE DEVELOPMENT OF A COMPUTER CODE TO SOLVE FOR THREE DIMENSIONAL FLOW OVER HELICOPTER ROTORS, INCLUDING CLOSE BLADE-VORTEX INTERACTIONS IS PROPOSED. THE METHOD INVOLVES A PREVIOUSLY DEVELOPED GRID-BASED FREE WAKE "VORTEX EMBEDDING" TECHNIQUE FOR TREATING VORTICITY TRANSPORT THROUGH MOST OF THE FLOW, AND A MODIFIED FINITE DIFFERENCE NAVIER-STOKES METHOD FOR THE REGION CLOSE TO THE BLADES. THE TWO METHODS USE THE SAME COMPUTATIONAL GRID, AND ARE SHOWN TO BE VERY SIMILAR. THIS SIMILARITY IS USED TO EFFECT A SMOOTH TRANSITION BETWEEN THEM, AND OBTAIN A UNIFIED SOLUTION METHOD. IN THIS UNIFIED SCHEME, THE VORTEX SHEETS SHED BY THE BLADES PROPAGATE WITHOUT NUMERICAL DIFFUSION THROUGH A RELATIVELY COARSE, ECONOMICAL GRID, MAINTAINING A FIXED INTERNAL STRUCTURE (USING THE EMBEDDING METHOD) AND CAN INTERACT WITH THE BLADES AT ANY DISTANCE, INCLUDING HEAD-ON INTERSECTION. DURING THE INTERACTION, DEFORMATIONS OF THE VORTEX AS WELL AS THE INFLUENCE ON THE BLADE BOUNDARY LAYER ARE TREATED USING THE NAVIER-STOKES EQUATIONS. A MODULAR APPROACH IS PROPOSED WHERE A NAVIER-STOKES ROUTINE AND A SPECIAL TRANSITION ROUTINE ARE TO BE DEVELOPED AND COUPLED TO OUR EXISTING VORTEX EMBEDDING CODE. FUTURE MODIFICATIONS OF THE EMBEDDING CODE WILL BE READILY ADAPTABLE TO THE PROPOSED MODULES.