Measurements of the flow field in a modern gas turbine combustor
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.