Exhaust mixer for turbofan aeroengine

Claim 1

An exhaust mixer of the multi-lobed type for a bypass gas turbine aeroengine whereby during operation of said aeroengine there is established a vortex system downstream of said exhaust mixer to encourage mixing between a bypass airstream and a turbine exhaust stream, said mixer comprising: a plurality of troughs and lobes, said troughs being located between said lobes, said troughs and said lobes comprising confronting pairs of flow surfaces, said flow surfaces having a progressive twist between their upstream and downstream ends such that said vortex system is established, said vortex system including vortices of said bypass air and said turbine exhaust trailing from said downstream ends of said flow surfaces, and vortex destabilising means including said twisted flow surfaces having downstream edges in the form of sinuous curves each having a single point of inflection, said sinuous curves producing substantial variations in the degree of twist of the downstream ends of the flow surfaces relative to their upstream ends, said bypass airstream and said turbine exhaust stream leaving the downstream edges of said flow surfaces with a substantial range of rotational velocity components and a substantial range of velocity components transverse to the streamwise direction of air and exhaust flow whereby said vortex system is rendered unstable and said vortices interact with one another to burst.