Jet-flap interaction noise in model scale and full scale - and the implications for evaluating noise reduction technologies

Abstract

Jet-flap interaction (JFI) noise consists of both broadband effects and tonal components. The frequency range of the tonal components can be characterized with a cut-on and cut-off frequency [1]. The JFI tones are well-audible and significant for the model scale engines. In addition to this, for very large commercial jet engines (e.g. UHBR class), the (in model scale) high-frequent broadband-like JFI-noise becomes very relevant in full scale. It can be shown that JFI noise spectra of different model size experiments collapse as expected: Two geometrically similar JFI-experiments were conducted at AWB (large scale) and JEXTRA (small scale) where the model geometries differ by a relevant factor (2.5). These results indicate, that it is safe to derive full scale spectra from experimental model scale spectra. In order to account for the human hearing, weighting functions can be applied. A sensitivity study wrt. height gives hints about the relevance of two different frequency ranges of JFI noise, JFI noise below and above the tonal cut-off frequency.