The noise-generating mechanism of rod-airfoil configuration and the effect of spanwise length on noise prediction

The wake-blade interaction in turbo-engines is the primary source of broadband noise. In this work, the noise mechanism of a benchmark rod-airfoil configuration is exhaustively analyzed using compressible Large Eddy Simulation (LES) and Ffowcs Williams-Hawkings (FW-H) methods. The baseline model with a spanwise length shortened by 7d (d is the rod diameter) is simulated under periodic boundary conditions, and the effect of spanwise lengths on noise prediction and correlation is investigated in combination with two other models (3d and 1d). In terms of the baseline model, the noise predicted by different FW-H surfaces is compared first, and the noise radiated from different chordwise and spanwise regions of the airfoil surface reveal the generating mechanism of the main dipolar noise and the effect of periodic boundary conditions on noise prediction, respectively. Additionally, the fluctuating surface pressure characterized at four frequency bands confirms that the wake-airfoil interaction dominates the leading-edge noise at low frequencies. The characteristic frequencies of the noise and transient velocity fields reveal that the primary broadband noise source is the interaction of large-scale vortices with the airfoil surface at the leading-edge region. Finally, the effect of spanwise length on noise prediction and correlation is studied for three models. The differences in the flow structures lead to different features of their coherence coefficients. The results presented in this work provide a comprehensive understanding of the noise-generating mechanism of wake-airfoil interaction in turbomachinery and the practical application of simplified models in the future numerical simulations.(c) 2023 Elsevier Masson SAS. All rights reserved.