Duct effects on rotor noise in radiation

Sound generation and radiation from the duct-rotor system are calculated numerically. The wake geometries of a two-bladed rotor are calculated by using a time-marching free-wake method without a non-physical model of the far wake. Acoustic free field due to a rotating rotor is obtained by Lowson’s equation. Using Kirchhoff source, rotating sources are modeled as stationary ones and can be inserted the frequency domain thin body boundary element method. The Kirchhoff source is validated through calculation of acoustic pressure due to a rotating point force. The thin body boundary element method (thin body BEM) is validated through comparison acoustic radiation of ducted dipole with analytic one. Using Kirchhoff source and thin body BEM, acoustic radiation of a ducted rotating source is calculated. Acoustic shielding is observed by inserting a duct and shows different phenomena at each major frequency. Acoustic radiation of a real duct-rotor system is also calculated using this method and the ducted acoustic field is significantly different from rotor only.