Jet-installation noise reduction with flow-permeable materials

This paper investigates the application of flow-permeable materials as a solution for reducing jet-installation noise. Experiments are carried out with flat plate placed in near field single-stream subsonic jet. The is modular and solid surface trailing edge can be replaced different inserts, such metal foam perforated structure. time-averaged jet flow characterized through planar PIV measurements at three velocities (Ma=0.3, Ma=0.5 Ma=0.8, where Ma acoustic Mach number), whereas far-field measured microphone arc-array. Acoustic confirm that installation effects cause significant noise increase, up to 17 dB lowest velocity, particularly low mid frequencies (i.e. St<0.7, Strouhal number based on diameter velocity), mostly upstream direction By replacing foam, abatement 9 achieved spectral peak Ma=0.3 polar angle ?=40?, an overall reduction entire frequency range dominant. provides lower than (7 ?=40?), it less effective frequencies. related values permeability form coefficient materials, which major parameters controlling pressure balance across and, consequently, generated by plate. However, despite having high permeability, metal-foam still has distinct production (St?0.43 Ma=0.3). Based analyses treated lengths, conjectured solid-permeable junction acts new scattering region, thus its position also affects noise, line analytical predictions literature. Nonetheless, both types inserts provide potential solutions problem