Wavepacket Modelling of Jet-Flap Interaction Noise: from Laboratory to Full-Scale Aircraft

A key component of aircraft acoustic installation effects relevant for under-wing turbofan-powered airliners, is studied: jet-flap interaction noise.

First, noise measurements performed on laboratory jets and on realistic engine exhaust geometries are analyzed to gain understanding both on surface pressure in the jet near-field and on far-field acoustics. The analysis of experimental datasets at various scales underlines intense, advecting, coherent and exponentially-growing pressure signatures in the jet near field and on the wing under-side. The outcome confirms our hypothesis for the main mechanism driving jet-flap interaction noise: coherent organized turbulent structures.

Relevant physical models are selected and chained together. RANS CFD and stability analysis model the characteristics of jet wavepackets as noise sources, analytical tailored Green’s functions and Boundary Element Method (BEM) predict the diffraction of the wavepackets by the airframe.

For academic configurations where a flat plate models the wing and flap, the wavepacket model is found able to capture noise directivity and trends. The significant impact of a swept trailing edge and the contributions of other plate edges lead us to design, test and simulate a plate with realistic wing plan form. The wavepacket-BEM simulation reproduces jet-surface interaction for the wing plan-form plate, as well as jet-flap interaction on realistic models tested at ONERA CEPRA19 facility during large-scale wind-tunnel tests. Wing-mounted unsteady pressure sensors are utilized as first control points. Then, polar and azimuthal acoustic directivity is examined. Discrepancies between experiments and simulations are identified. Finally an installation geometrical effect is computed: the vertical separation H between nozzle and wing is varied to replicate the tests.

The diffraction of coherent organized turbulent structures generates jet-flap interaction noise in the academic jet laboratory, in large-scale wind-tunnel test and on the full-scale aircraft. We conclude on the potential and the limits of the proposed wavepacket-BEM model to predict the sound field, and we outline the perspectives for future modelling and testing.