Investigations on acoustic characteristics of rotor with improved CLOR bladetip in hover based on experimental and prediction method

The aeroacoustic characteristics of model rotor with improved CLOR (CLORII) bladetip in hover are investigated through tests and numerical simulations. Firstly, the shape of rotor blade is improved based on CLOR bladetip considering both aeroacoustic characteristics and aerodynamic performance. In order to obtain preferable aerodynamic performance (high rotor thrust) and suppress the rapid increase of rotor noise, curvilinear forwardbackward swept, taper and airfoil configuration are adopted so that the transonic region is restrained and the noise level of rotor is decreased. Then, the aeroacoustic characteristics of rectangular planform blade and constant swepttip blade with the same solidity are measured in present work for validation. In consideration of the effects of radiation distance and orientation angle (inclined to rotor disk plane) on acoustic characteristics of rotor, acoustic measurements are conducted at different observation locations in tests. Furthermore, acoustic measurements are carried out at various rotor rotation speeds to evaluate the influence of blade tip Mach number (compressibility) on acoustic characteristics of rotor. Finally, a rotor acoustic analysis approach based on CFD/Kirchhoff method is established, and the acoustic characteristics of CLORII bladetip have been comprehensively investigated under high blade tip Mach number conditions which are difficult to be conducted in tests. Details of the transonic flowfield of abovementioned bladetips, such as Mach contour and nearfield pressure contour, are provided respectively. Through tests and numerical analysis, the effects of CLORII bladetip on aeroacoustic characteristics are obtained, and rotor with the present advanced tip can simultaneously enhance aerodynamic performance and retain better acoustic characteristics comparing to reference rotors.