Suppression mechanism investigations on BVI noise of rotor with anhedral blade tip

In order to capture the formation and evolution of blade tip vortex and blade vortex interaction (BVI) events, the high-fidelity hybrid TENO8-THINC reconstruction scheme is proposed to simulate unsteady flowfield of rotor. The hybrid scheme ensures robustness and stability in capturing the discontinuities while minimizing numerical dissipation in the smooth regions dominated by the tip vortices, thus significantly improving the detail capture ability of vortex field and providing accurate aerodynamic input for noise prediction. The noise characteristics of BVI state and non-BVI state are newly investigated by decomposing Farassat 1A formula into thickness, load amplitude and load derivative terms, and the results demonstrate that the dominant factor of BVI noise is the load derivative term. Then, the sound pressure time histories of oblique and parallel interaction regions of OLS rotor in BVI state are calculated and compared, and it indicates that oblique interaction on the advancing side has the greatest influence on BVI noise. Finally, parameter analysis of the influence of anhedral tip blades on BVI noise is carried out, illustrating that anhedral blade divides the main blade tip vortex into two vortex systems with similar intensity, which alleviates the strength of oblique interaction on the advancing side and parallel interaction, so as to achieve the purpose of BVI noise reduction, and the reduction of sound pressure level is nearly 5 dB.