ANALYSIS OF MAIN-ROTOR-WAKE/TAIL-ROTOR INTERACTION NOISE

THE IMPORTANCE OF REDUCING THE NOISE OF THE HELICOPTER TAIL ROTOR HAS BEEN RECOGNIZED FOR MANY YEARS. HOWEVER, BOTH THE PREDICTION OF TAIL-ROTOR NOISE AND THE DEVELOPMENT OF LOW NOISE DESIGNS HAS BEEN IMPEDED BY POOR ABILITY TO SIMULATE NOISE-GENERATING INTERACTIONS BETWEEN THE MAIN-ROTOR WAKE AND THE TAIL ROTOR. IN MANY CASES, EVEN THEFLIGHT CONDITIONS LEADING TO SUBSTANTIAL MAIN-ROTOR/TAIL-ROTOR INTERACTION HAVE BEEN DIFFICULT TO DETERMINE. RECENT ADVANCES IN THE MODELLING OF FREE-VORTEX WAKES AT CONTINUUM DYNAMICS, INC. HAVE GENERATED TOOLS THAT CAN AMELIORATE THIS SITUATION. FULL-SPAN FREE WAKE MODELS FOR ROTOR BLADES HAVE BEEN DEVELOPED THAT CAN GENERATE COMPLETE DESCRIPTIONS OF THE INCIDENT-VORITICITY FIELD IN THE VICINITY OF THE TAIL ROTOR. CURVED VORTEX ELEMENTS ARE USED IN THIS WAKE MODEL AND PRODUCE HIGHLY ACCURATE DESCRIPTIONS OF THE LOCAL VELOCITY FIELD. IN LIGHT OF PREVIOUS SUCCESSES IN TREATING HIGH FREQUENCY AIRLOADS ON MAIN ROTORS, IT IS ANTICIPATED THAT THE COUPLINGOF THESE NEWLY DEVELOPED TOOLS TO APPROPRIATELY MODIFIED VERSIONS OF EXISTING BLADE LOAD ANALYSES CAN PRODUCE A COMPUTATIONAL SIMULATION CAPABLE OF PROVIDING IMPROVED DEFINITION OF MAIN-ROTOR/TAIL-ROTOR INTERACTIONS AND THE RESULTING UNSTEADY LOADS THAT LEAD TO STRONG ACOUSTIC EMISSIONS.