This paper is concerned with the design and performance of an annular S-shaped duct that would be used to connect an LP fan to the core within a gas turbine engine. The desire to minimise engine length means the duct is of relatively short length so that, without novel design, flow separation is likely to occur. Hence the upstream OGV row has been leant tangentially so that it assists in turning the flow within the first bend of the S-shaped duct. In such an ‘integrated’ design, a component of the lift force generated by the OGV row turns the flow radially inward. In this way, the aerodynamic loading on the critical inner wall boundary layer, within the downstream S-shaped duct, is reduced. In addition, by incorporating the blade row within the duct, rather than upstream of it, a further length reduction can also be achieved. The paper outlines the OGV design methodology and presents experimental results that define the aerodynamic performance of the integrated system. The overall system loss is determined mainly by the OGV row, and the subsequent mixing out of the blade wakes prior to the inlet of the core duct. In addition, for the range of conditions tested, the stagnation pressure profile at core duct exit reflects that portion of the OGV exit profile that is captured by the core duct.

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