An experimental investigation has been carried out to determine the effects of inlet swirl on the flow field that develops within an annular S-shaped duct. The duct is representative of that used to connect the compressor spools on multi-spool gas turbine engines. By removing the outlet guide vanes from an upstream single stage compressor swirl angles in excess of 30° were generated. Results show that within the S-shaped duct tangential momentum (Wr) is conserved, leading to increasing swirl velocities through the duct as the radius decreases. Furthermore, this component influences the streamwise velocity as pressure gradients are established to ensure the mean flow follows the duct curvature. Consequently in the critical region adjacent to the inner casing, where separation is likely to occur, higher streamwise velocities are observed. Within the duct substantial changes also occur to the turbulence field which results in an increased stagnation pressure loss between duct inlet and exit. Data is also presented showing the increasing swirl angles through the duct which has consequences both for the design of the downstream compressor spool and of any radial struts which may be located within the duct.

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