Patent ID: 7018166

Claim:
A duct assembly comprising a circular duct and an axial flow free rotor on a downstream side thereof; said duct being open at both ends and adapted to substantially separate a unidirectional fluid stream into an inner partial stream within the duct and an outer partial stream outside the duct; said duct having an inner surface comprising a convergent surface and a divergent surface; said free rotor having a hub with a plurality of arms extending radially outwardly from said hub wherein each of said arms comprises a radially outer portion and a radially inner portion; the radially inner portions terminating at a ring having through passages connecting the inner stream to the outer stream; said ring having a radially inner surface at an upstream edge thereof, adjacent the radially inner surface of said duct at the downstream edge thereof; and the radially outer portions extending from said ring and comprising blades responsive to said outer partial stream to cause the free rotor to rotate unidirectionally in use; and wherein said free rotor includes extraction means adapted to draw fluid from said inner partial stream along the divergent surface of the duct towards the free rotor from the upstream side thereof, and to cause a part of said inner partial stream to flow radially outwards via said ring to mix with said outer partial stream moving downstream of the free rotor; the fluid drawn through the through passages of the ring from the inner stream to the outer stream causing a redistribution of flow through the duct so as to provide boundary layer control to prevent premature separation of fluid along the inner surface of the duct.