Abstract
New ultra high bypass ratio architectures may significantly affect the fan tonal noise of future aircraft engines. Indeed, such a noise source is supposed to be dominated by the interaction of fan-blade wakes with outlet guide vanes. However, shorter nacelles in these engines are expected to trigger an important air-inlet distortion that can be responsible for new acoustic sources on the fan blades. Full annulus simulations based on the unsteady Reynolds-averaged Navier–Stokes equations are presently used to study this effect. Simulation results show that the air-inlet distortion has a main effect in the fan-tip region, leading to a strong variation of the fan-blade unsteady loading. It also significantly modifies the shape of the fan-blade wakes and, consequently, the unsteady loading of the outlet guide vanes. Acoustic predictions based on the extension of Goldstein’s analogy to an annular duct in a uniform axial flow are presented and show that the fan sources notably contribute to the fan tonal noise. The air-inlet distortion is responsible for an increase of the noise radiated by both the fan and the outlet guide vane sources, leading to a global noise penalty of up to three decibels.
Highlights
Fuel consumption and noise reduction trigger the evolution of aircraft engines towards ultra high bypass ratio (UHBR) architectures
The influence of distortion on fan tonal noise at the cutback condition has been successfully investigated in a realistic UHBR configuration
Such a tonal noise is assumed to be dominated by the interaction of fan-blade wakes with the outlet guide vanes (OGVs)
Summary
Fuel consumption and noise reduction trigger the evolution of aircraft engines towards ultra high bypass ratio (UHBR) architectures. Because the nacelles that hold these engines are expected to be larger than the current ones, their weight and drag must be controlled. This can be achieved by shortening their lengths in two different ways. The geometry of the nacelle is asymmetric to account for the downward deflection of the flow by the wing Due to this asymmetry, a distortion is created when the flow is ingested. A distortion is created when the flow is ingested This distortion will not be sufficiently damped before reaching the fan because of the reduced length of the air inlet. Whatever solution is adopted for reducing the length of the nacelle will have an impact on the distortion level and might alter the acoustic radiation of the fan significantly
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