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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.

The computer simulation of flow separation from bluff bodies is achieved by a method which solves the two dimensional incompressible Navier-Stokes equations using clouds of point vortices. The vortices convect each other, and have an additional random motion to represent viscosity, as originally proposed by A. J. Chorin. Some justifications for the introduction of randomness as the agent of entropy production are presented. The method is applied to some simple boundary layer simulations, and then in combination with an integral equation method due to E. Martensen , the flow around bluff bodies of arbitrary shape is simulated in order to predict lift and drag. The stalling characteristics of aerofoil NACA 0012 are reproduced from first principles by computer simulation, and the results compared to experiment. The dependency of the Strouhal number against Reynolds number for the von Karman vortex street behind a circular cylinder is also investigated by simulation. An attempt is made to simulate the phenomenon of rotating stall which appears in curpressors as the first sign of aerodynamic overloading.

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No description available.

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No description available.