Abstract
In future Ultra-High By-Pass Ratio turboengines, the turbomachinery noise (fan and turbine stages mainly) is expected to increase significantly. A review of analytical models and numerical methods to yield both tonal and broadband contributions of such noise sources is presented. The former rely on hybrid methods coupling gust response over very thin flat plates of finite chord length, either isolated or in cascade, and acoustic analogies in free-field and in a duct. The latter yields tonal noise with unsteady Reynolds-Averaged Navier–Stokes (u-RANS) simulations, and broadband noise with Large Eddy Simulations (LES). The analytical models are shown to provide good and fast first sound estimates at pre-design stages, and to easily separate the different noise sources. The u-RANS simulations are now able to give accurate estimates of tonal noise of the most complex asymmetric, heterogeneous fan-Outlet Guiding Vane (OGV) configurations. Wall-modeled LES on rescaled stage configurations have now been achieved on all components: a low-pressure compressor stage, a transonic high-pressure turbine stage and a fan-OGV configuration with good overall sound power level predictions for the latter. In this case, hybrid Lattice–Boltzmann/very large-eddy simulations also appear to be an excellent alternative to yield both contributions accurately at once.
Highlights
Significant reductions of aircraft noise have been achieved in the past decades, mostly by reducing jet noise
A comparison between the above analytical model and the unsteady Reynolds-Averaged Navier–Stokes (u-RANS) results is shown in Figure 4 for both the blade response and the sound power level radiated upstream at the first blade passing frequency (BPF)
A strong dipolar source is seen at the stator vane leading edge, and a weaker high-frequency source is coming from the rotor trailing edge
Summary
Significant reductions of aircraft noise have been achieved in the past decades, mostly by reducing jet noise. The noise from the fan is expected to become the main noise source of future aircrafts at least in the forward arc, and at almost all flight conditions [1]. Another foreseen evolution in turbofan technology is the reduction of the number of stages in the turbine. Having more highly loaded turbine rows yields more intense tonal and broadband turbine noise, often shifted to more annoying frequency bands with less stage filtering and lining efficiency [2] This has led to what Nesbitt calls the “turbine noise storm” in modern Low Pressure
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