The estimate of helicopter rotor noise from unsteady forces

Abstract

The cost-efficient method to calculate the sound pressure due to main rotor unsteady forces in far acoustic field is proposed. As it is known, the evaluation of the sound pressure in relation to time allows estimating the main rotor acoustic characteristics. The paper aims at the enhancing the green safety of advanced helicopters and those being up-graded ones. The mathematical simulation of rotor noise emission is needed both to find out the phenomena physical essence (currently there is no unanimous opinion in re of noise emission processes of several types) and to predict analytically the rotors acoustic characteristics or the rotors combinations at different flight regimes. The unsteady load on the main rotor blade components is used in the proposed method that is based on Ffowcs Williams –Hawkings equation to calculate the sound pressure that is generated by main rotors [1, 2]. This load is estimated by calculation method based on non-linear theory of main rotor in non-stationary statement [3-5]. Such an approach is recognized as the most rational when constructing the methods of main rotor sound characteristics calculation because the rotation noise and the non-stationary noise constituents are taken into consideration including the load spikes conditioned by the interaction between the blade and the ahead blade tip vortex (BVI). Therefore the integrated analytic research is performed of rotation noise and vortex noise.