22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-3.9.4

INFLUENCE OF ARBITRARY VORTICAL WAKE EVOLUTION ON FLOWFIELD AND NOISE GENERATION OF HELICOPTER ROTORS

A. J. Spyropoulos, A. P. Fragias, D. P. Margaris, D. G. Papanikas
Fluid Mechanics Lab., Mechanical Engineering and Aeronautics Department, University of Patras, Greece,

Keywords: helicopters, rotor aerodynamics, rotor aeroacoustics

This paper presents a combined methodology consisting of rotor aerodynamic and aeroacoustic computation modules. Aerodynamic calculations utilise the Vortex Element Method for the description of free vortex wake, which determines the rotor flowfield. The mathematical model discretizes the wake into vortex elements. The induced velocity is calculated for the distorted wake geometry, by means of the Biot-Savart law, integrated in closed form over each of these elements. Bound circulation variations and unsteady blade airloading are computed as a result of the nonuniform induced downwash. Wake roll up process, vortex core modelling, vorticity dissipation, blade section boundary layer growth are incorporated in numerical modelling of aerodynamic computations. Computed blade loading variations are used as the basis of loading noise predictions. Aeroacoustic analysis concentrates on helicopter rotor noise prediction in time domain. The formulation is based on the Ffowcs-Williams and Hawkings (FW-H) equation modelling only thickness and loading noise by integrating monopole and dipole sources over the blade surface at subsonic tip speeds. The developed computational procedure demonstrates the influences of the highly complicated rotor flowfield to noise generation. Blade airloading, acoustic and sound pressure level results are demonstrated and compared with experimental data, showing a fairly good agreement between measurements and predictions.

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