10th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
A hybrid method combining a three-dimensional unsteady RANS simulation of a cropped CROR at approach conditions and an acoustic analogy based on a frequency formulation of the Ffowcs-Williams and Hawkings analogy, originally developed by Hanson and extended to non compact chord length, has shown three main sources, the impacts of the front-rotor wakes on the rear-rotor, of the front-rotor tip vortex on the rear-rotor tip, and of the front-rotor hub horse-shoe vortex on the rear-rotor foot. Consequently, this study confirms that the rear-rotor is the dominant tonal noise source and has identified another potential noise source when the CROR is installed caused by the strong tip vortex of the highly-loaded cropped rear-rotor. The rotor-rotor distance should not be reduced as the potential effect is already felt on the front rotor. The influence of the grid refinement has been evaluated on both aerodynamic and acoustic performances.