Investigation of noise from full-scale high bypass engine and blown flap system

A summary is presented of an acoustic test program for investigating engine noise suppression and jet/flap interaction noise associated with an externally blown flap (EBF) STOL powered lift system. A highly suppressed TF-34 engine and EBF wing were used in the investigation. The engine was suppressed 21 PndB to a level of 94 PndB. An under the wing (UTW) powered lift system was tested with conventional, mixer, and decayer-type nozzles. The configuration with velocity decayer nozzle and acoustically treated shroud had the lowest noise (98 PndB). An over the wing (OTW) configuration with nondecayer nozzle was about 10 dB quieter than the corresponding UTW system. UTW and OTW noise data are compared with scale model correlations.