The performance of compressor outlet guide vanes and downstream diffuser

A large-scale compressor/diffuser test rig has been designed and constructed which,. together with an automated data acquisition system, permits more detailed and more accurate measurements than were previously possible - especially in the region of the compressor OGV's. Results are presented based on experiments carried out using two different single-stage axial-flow compressors operating immediately upstream of a straight-core annular diffuser, each compressor being tested with a conventional stator row and a double-dihedral chevron type of stator row i.e. four main configurations were investigated. In addition to these main tests, the effects of operating the stator row at low Reynolds number, and of operating the stator row with a small hub clearance have been investigated. The chevron OGV shows a clear improvement, compared to the straight OGV, in t=s of diffuser performance and diffuser exit velocity profiles, at the expense of a general tendency for the OGV loss to increase. When hub clearance is used on a straight OGV, a hub corner stall arises, but this can be eliminated by incorporating blade dihedral at the hub. It seems likely that further improvements in diffuser exit conditions could be achieved by . careful design of the blade shape to encourage radial movement of flow. Traversing within the blade passage, for a straight type OGV, has revealed significant vortices rotating in the opposite sense to classical curved duct secondary flows.