Bluff body noise control using perforated fairings

Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using fairings to shield components from high-speed impingement reduces noise. Furthermore, perforating these fairings has been confirmed by flight tests to enable a further reduction. A fundamental study has been performed to investigate and optimize the benefits of bleeding air through the fairing by application of perforations. Experiments have been performed with a simplified fairing-strut combination to clarify the influence of perforations on flow behavior and acoustics. The fairing self-noise is reduced significantly by breakdown of the vortex shedding process, resulting in a reduction of the associated broadband noise level. A redistribution of the velocities is achieved depending on the applied porosity. However, increasing the porosity can result in adverse noise effects due to the bled mass flow washing the strut. Self-noise of the perforations manifests itself at higher frequencies, although scaling of this phenomenon with orifice diameter opens up the possibility to shift it above the upper limit of the audible range