Influence of compressor exit conditions on combustor annular diffusers. II - Flow redistribution

In gas-turbine engines the velocity of air, issuing from the compressor, must be reduced in order to permit effective operation of the downstream comhustor. This is partly achieved by locating an annular diffuser behind the compressor outlet guide vanes (OGVs); in modern systems, the inlet of this diffuser is usually located at the trailing edge of the blade row. This paper is concerned with some of the interactions that occur between these components and, in particular, the flow redistribution that occurs along the diffuser length due to the flows generated by the OGV blade passage and upstream rotor. A mainly experimental investigation has been undertaken, on a fully annular facility, which incorporates a single-stage axial flow compressor and simulated flame tube. The OGV blade row produces a profile that, as a result mainly of the blade wakes, contains an excess of kinetic energy relative to that of a uniform profile. The mixing out of these wakes therefore enhances the pressure rise within the downstream diffuser. Measured mean velocity data are used to determine the path of streamlines along each diffuser and indicate regions where high-energy fluid is being convected, toward each casing, and low-energy boundary layer fluid is being removed. (Author)