Attenuation of slat trailing edge noise using acoustic liners

Noise generated by high-lift devices such as the slats on the leading edge of a wing is a major contributor to the overall airframe noise during the landing approach of a commercial aircraft. In this work the concept of attenuating noise sources located at the trailing edge of a slat using absorptive acoustic liners in the slat gap is explored using a time-domain computational aeroacoustic (CAA) scheme. The aim of the computational modelling is to demonstrate the feasibility of controlling slat noise using acoustic liners, and to optimize the design for a future experiment. A model scale three-element high-lift airfoil is modelled; the slat and flap deflection angles are 23 deg and 32 deg respectively and the slat has a blunt trailing edge. The freestream Mach number is 0.2 and the main element angle of attack is 5 deg, corresponding to a typical approach condition. The Reynolds number is 3.6 million, based on the airfoil chord with the high-lift devices retracted. The computational results are divided into three parts: (1) an unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation using high-order spatial and temporal schemes is conducted for a wing without acoustic liners; the computed flow shows the presence of vortex shedding and acoustic sources behind the slat trailing edge; (2) a calculation of the radiated sound field is made for a range of liner impedance values by solving the linearised Euler equations (LEE) for a modelled acoustic source located at the trailing edge of the slat; (3) URANS computations for the wing with liner treatment are conducted. The results show that acoustic liners on the slat cove and on the main element can provide useful attenuation of slat trailing edge noise. 1