Slat Noise Suppression With Upstream Mass Injection

A numerical investigation into the suppression of slat noise has beenconducted with upstream mass injection near the slat cusp. The efficiency andmechanism of noise attenuation with upstream mass injection is studied in ahybrid approach. Delayed Detached Eddy Simulation is performed todescribe the noise sources of a two component high-lift model, FREQUENZ;Ffowcs-Williams and Hawking’s integration is employed to obtain thefar-field aeroacoustic characteristics. Results show that with injection,aerodynamic capability of the high-lift devices is sustained and a delightfulbroad band and tonal noise attenuation is observed with upstream normalmass injection, and a more or less suppression of the four tonal noise and theintroduction of two new tonal noise is presented with upstream parallel massinjection. With detailed analysis of the time-averaged and instantaneous flowfields, two mechanisms are identified as the reasons accounting for the noiseattenuation with upstream normal mass injection. Normal mass injectionuplifts the free shear layer, correspondingly, the time-averaged reattachmentpoint is pushed toward the upper trailing edge, the impingement of the freeshear layer and the slat pressure surface is alleviated, meanwhile, the freeshear layer keep continuous in a longer distance, and fewer vortices areinjected through the slot; Parallel mass injection reduces the scale andstrength of vortices near the slot, while introduces a high-intense unsteadyflow between the injected high-speed mass flow and gap flow.