Aerodynamics of high performance turbine blading

A major addition to European research facilities is the Oxford University Engineering Laboratory (O.U.E.L.) blowdown tunnel which can provide full-scale Reynolds and Mach number simulations on large and small models of turbine stage components. The facility was designed to provide extended aerodynamic capabilities to complement the existing heat transfer research in the Isentropic Light Piston Tunnel (ILPT) at O.U.E.L. The blowdown tunnel will be used for fundamental investigations of the boundary layers and flow fields around turbine blades in a linear cascade. The study of these flow fields is necessary for the prediction of heat transfer rates and for the optimisation of materials and cooling schemes required to improve gas turbine efficiencies. As a commissioning exercise measurements were made on cascades of similar geometry to those which had been previously tested in the ILPT and in other European facilities in order to compare results and analyse differences which occur due to the influence of tunnel geometry. Measurements made on various rotor profiles identified regions on the suction surface where surface pressure data is sensitive to the various types of exit plenums and exit pressure gradients. A second phase of work included measurements and a theoretical study of the boundary layer on a large-chord turbine rotor profile. Measurements on the pressure surface of the blade suggested the presence of secondary longitudinal vortices which rapidly lose an identifiable structure towards the trailing edge. On the suction surface, boundary layer measurements were compared with theoretical models, and it was shown that current numerical models of compressible turbulent boundary layers approximately correspond with the data. An adjunct to the boundary layer work was research on the use of a hot-wire anemometer, intended for future boundary layer measurements, and for which calibration laws and temperature effects were studied.