Abstract: The exhaust mixer can be classified as being of the multi-lobed type, with troughs between the lobes. The lobes and troughs comprise confronting pairs of flow surfaces which are twisted between their upstream and downstream ends such that a vortex flow system is established downstream of the mixer to encourage mixing between the bypass airstream and the turbine exhaust stream. The downstream edges of the twisted flow surfaces are in the form of sinuous curves which destabilize the vortex system and cause the vortices to burst, hence increasing the mixing efficiency.