Diagnostics and reduction of propulsion airframe aeroacoustic interactions

Abstract

In the past, significant reduction in aircraft noise has been achieved by studying engine noise and airframe noise in isolation as two separate components. However, when an engine is installed on an aircraft the flow and acoustic interactions between them produce a total noise signature which is often different than the sum of the component noise signatures. While take-off conditions are typically dominated by engine noise, approach conditions are characterized by both engine and airframe noise. Nevertheless, propulsion airframe aeroacoustic (PAA) interactions are present under all conditions and gain in importance when engine or airframe noise is further reduced. This paper focuses on the diagnostics and reduction of the flow-acoustic interaction effects between an engine exhaust and the airframe, especially the high-lift system on wings. Flow and acoustic results are presented for an isolated scale-model nozzle in a free jet, and also when it is installed under a wing at take-off and approach conditions. The difference between these two noise signatures, in the far field and at the source, captures the PAA effect. In particular, the PAA effect due to changes in nozzles, pylons, and flaperons is presented and the overall noise reducing mechanisms are postulated.