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We present an initial parametric investigation of fan flow deflectors for suppressing noise from supersonic turbofan engines. Realistic exhaust geometry and flow conditions for bypass ratio 2.7 were simulated in a subscale experiment. The study encompassed acoustic measurement and mean velocity surveys. The deflectors comprised internal vanes with both symmetric and cambered airfoil sections and deployable external flaps. Superior acoustic results were achieved using a combination of cambered vanes and perforated flaps, yielding cumulative (downward plus sideline) EPNL and OASPL reductions of 7.7 dB and 9.2 dB respectively. A fair correlation is established between the suppression of peak OASPL and the reduction of the radial velocity gradient on the underside of the jet.

We present an experimental study, comprising acoustic and mean-flow measurements, of several fan-flow deflector configurations in a subscale dual-stream supersonic turbofan nozzle. The deflectors encompassed internal vanes and external wedges. The aim of the study was to investigate trends of high-frequency noise reduction, in the direction of peak emission, versus the distortion of the velocity field in the jet plume. The distortion is quantified in terms of the volume of the inflectional region of the jet, in a particular azimuthal direction, normalized by the volume of the high-speed region of the jet. It is observed that fan flow deflection generally increases the volume of the inflectional region (in the downward and sideline azimuthal directions) and decreases the volume of the high-speed region. Correlations of sound pressure level with the volume-ratio parameter show rapid noise suppression for small values of the volume ratio followed by slower noise reduction at higher values. The correlations appear to validate the hypothesized physics of noise suppression by an enlarged secondary core, and provide practical guidance for the implementation of the fan flow deflection method Nomenclature

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