Flow Control in an Inter-Turbine Duct

Inter-turbine ducts experience flow separation along their outer wall when either the radial offset from the inlet to the outlet is increased or the axial length is decreased. Decreasing the axial length of this annulus not only reduces overall engine weight but can potentially increase performance in low pressure turbine stages. Two aggressive inter-turbine duct geometries differing in axial length but sharing identical inlet and outlet cross-sectional areas were tested at an inlet Mach number of 0.3. Velocity and turbulence intensity measurements were taken inside both inter-turbine ducts through a narrow window by means of Laser Doppler Velocimetry. Flow separation occurred in regions where the duct depth increased rapidly and where the shroud wall maximum angle reaches a noticeable peak. Delta-shaped passive vortex generators were able to reduce the size of the separation bubble by up to 22%. Previous research of plasma actuators has shown reductions of a separation bubble on a concave surface. An azimuthal strip plasma actuator was designed on a stereolithography dielectric insert that follows the contour of the duct shroud. The designed model allows for documentation of flow reattachment inside the duct downstream of the body force vector.