Evaluation of the Noise Reduction Potential of a Krueger Flap High-Lift device via the Lattice Boltzmann Method

Abstract

Main objective of this work is to conduct Direct Noise Computation of high-lift wings using wall-modeled LES with LBM. For this purpose, we employ an industrial LBM software ProLB. In our previously reported work, we presented a quantitatively successful validation of a conventional high-lift wing (DLR/ONERA F16). This study carries forward our high-lift noise investigation, now with a Krueger flap as an alternative high-lift device that has been proposed elsewhere for the laminar wing concepts. Aeroacoustically, in the absence of noise-generating mechanisms that are typically present at the conventional slat i.e. interacting and impinging shear layers, this design provides a potential for noise reduction. For this study, we use two different Krueger flap designs: reference and aerodynamically optimized Krueger. Reference Krueger has a short chord while the optimized Krueger has a long chord. These multi-element, unswept high-lift wings with deployed Krueger flap and flap are resolved on a mesh with 5%clean chord length spanwise extent. Periodic boundary condition is applied along the spanwise direction. For the relative accuracy, the time-averaged near field WM-LES results for both the Krueger flap variants are compared with the RANS. Far field acoustic comparison is carried out between the conventional slat (F16) and both the Krueger leading edge devices. Optimized Krueger shows a noise reduction potential over the reference Krueger and conventional slat based design. Further noise reduction potential is observed when the cavity for Krueger flap to stow back is closed in the simulation. It is found that the stowage cavity contributes to the overall noise radiation for frequencies higher than 3 kHz. Additional improvement towards tackling of the periodicity effect in the direct noise computation of high-lift approaches is reported. Periodicity introduces a cut-on type jump in the pressure spectrum. A new approach is introduced for the specific spanwise periodic setup that cancels excess energy induced by the additional cut-on modes.