2019 Volume 18 Pages 207-216
In this study, we proposed an empirical noise evaluation parameter for a slat in a three-element high-lift airfoil to design a low-noise high-element airfoil with minimal evaluation cost. In our proposal, we focused on the distance from the trailing edge to the reattachment position of a shear layer emanating from the slat cusp, which can be estimated using Reynolds-averaged Navier Stokes (RANS) simulations and represents the size of the circulation region in a slat cove. To investigate this assumption and to evaluate the noise characteristics, Ffowcs-Williams and Hawkings' far-field and delayed-detached eddy simulations were conducted. We found that the lower the noise observed in real scale, the longer was the distance. In addition, we also found that a remarkable relationship exists between this distance and broad-band noise. We then attempted a multi-objective optimization using a Kriging model based on an evolutionary algorithm. The objective was to maximize the distance to reduce the broadband noise and maximum lift. Based on the optimization, 27 cases in which the slat position was changed were evaluated through RANS simulations to construct the Kriging model. The optimization results reconfirmed that slat overlap has the largest effect on the distance from the trailing edge to the reattachment position. These results suggest that the optimum slat position to achieve noise reduction can be achieved without reducing maximum lift.
