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A detailed investigation into the aerodynamics of a modern gas turbine combustor is reported in this thesis. The main objectives of this work were to examine the interactions between the various features of the internal flow field, and between the external and internal aerodynamics, and to obtain sufficient flow field data for validation of CFD codes. A new experimental facility was developed to allow optical access for high quality internal and external measurements of the isothermal flow field in a three sector segment of an annular gas turbine combustor whose geometry is typical of the combustors in use in current turbofan engines. A specialised traverse system was designed to enable measurements of the flow field by a three component Laser Doppler Anemometry (LDA) system, and a considerable effort was made to maximise the accuracy of the LDA system. Measurements of three orthogonal mean velocity components and all six Reynolds stresses were obtained throughout a burner sector of the combustor. A set of data has been obtained that is sufficiently extensive for use as a benchmark data set for CFD validation. Measurements in the feed annuli showed that the behaviour of the flow was as expected. Internal measurements revealed a strong coupling between the flow in the feed annuli and the flow entering the flame tube through primary and secondary ports. Differences in the geometries and flow splits in the inner and outer annuli caused significant differences between the opposed jets inside the flame tube. The initial pitch angle and axial and radial momentum components of the jets were found to be strongly dependent on the ports' feed conditions. Differences between the opposed jets, due to differences in their feed conditions, affected the location of their impingement and the trajectory of the jet fluid after impingement. The impingement process was also found to be unstable. The centre primary jets, which are downstream of the fuel injector, displayed a dramatically increased sensitivity to their feed conditions, caused by the low pressure in the recirculation induced by the swirler. This caused the jets to be deflected in opposite directions, with no impingement. The flow field in the primary zone was thus substantially altered, with serious implications for the performance of the combustor. These results also demonstrate the importance of coupling the internal and external flows in all experimental and computational models.

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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