Numerical study of acoustic source localization of rotor using a novel discrete noise analysis strategy

In order to obtain the influence mechanism of the rotor noise and the local aerodynamic variation under different operating conditions, a novel discrete noise analysis strategy for the acoustic source localization is established. The analysis strategy has two aspects including the blade division method and the noise contribution calculation method. Firstly, the body-fitted rotor blade grids are preprocessed and refined at the division position before the flowfield simulation. Then, based on the flowfield result, the blade grids are divided into several blocks in the chordwise and spanwise directions, and the acoustic pressure of each block is predicted. Finally, a discriminant function for the contribution of the block to the rotor noise is proposed, and the acoustic source localization is carried out. The URANS equations and FW-H equations are used to capture high-fidelity flowfield and rotor acoustic pressure. Parameters such as the block position in different direction on the rotor blade and the collective pitches are quantified, and the relationship between air flow and aeroacoustics is discussed in detail. Some conclusions are obtained by analyzing the BO105 model rotor in hover. The acoustic pressure produced by the leading edge of the upper surface could cancel about 50% acoustic pressure of the remainder of these blocks. Increasing the force at this position will be benefit to the noise reduction. Acoustic source distribution is closely linked to the flow separation near the blade tip: the main acoustic source moves toward around 0.9 R section of the blade in the spanwise direction, and it moves from the leading edge towards the trailing edge in the chordwise direction.