The paper uses experimental measurements to characterise the extent that improved external aerodynamic performance (reduced total pressure loss, increased flow quality) of a gas-turbine combustion system may be achieved by adopting an integrated OGV/pre-diffuser technique. Two OGV/pre-diffuser combinations were tested. The first is a datum design corresponding to a conventional design approach, where OGV and pre-diffuser are essentially designed in isolation. The second is an ‘integrated’ design where the OGV blade shape has been modified, following recommendations of earlier CFD work ([14]), to produce a secondary flow/wake structure that allows the pre-diffuser to operate at a higher area ratio without boundary layer separation. This is demonstrated to increase static pressure recovery and reduce dump losses. Experimental measurements are presented on a fully annular rig. Several traverse planes are used to gather 5-hole probe data which allow the flow structure through the OGV, at inlet and exit of the pre-diffuser, and in the inner/outer annulus supply ducts to be examined. Both overall performance measures (loss coefficients) and measures of flow uniformity and quality are used to demonstrate that the integrated design is superior.

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