THE DEVELOPMENT OF FAST-RESPONSE AERODYNAMIC PROBES FOR FLOW MEASUREMENTS IN TURBOMACHINERY

The advent of a new generation of transient rotating turbine simulatio n facilities, where engine values of Reynolds and Mach number are matc hed simultaneously together with the relevant rotational parameters fo r dimensional similitude (Dunn et al., 1988; Epstein and Guenette, 198 4; Ainsworth et al., 1988), has provided the stimulus for developing i mproved instrumentation for investigating the aerodynamic flows in the se stages. Much useful work has been conducted in the past using hot-w ire and laser anemometers. However, hot-wire anemometers are prone to breakage in the high-pressure flows required for correct Reynolds numb ers. Furthermore, some laser techniques require a longer run-time than these transient facilities permit and generally yield velocity inform ation only, giving no data on loss production. Advances in semiconduct or aerodynamic probes are beginning to fulfill this perceived need. Th is paper describes advances made in the design, construction, and test ing of two and three-dimensional fast response aerodynamic probes, whe re semiconductor pressure sensors are mounted directly on the surface of the probes, using techniques that have previously been successfully used on the surface of rotor blades (Ainsworth et al., 1991). These a re to be used to measure Mach number and flow direction in compressibl e unsteady flow regimes. In the first section, a brief review is made of the sensor and associated technology that has been developed to per mit a flexible design of fast response aerodynamic probe. Following th is, an extensive program of testing large-scale aerodynamic models of candidate geometries for suitable semiconductor scale probes is descri bed and the results of these discussed. The conclusions of these exper iments, conducted for turbine representative mean and unsteady flows, yielded new information for optimizing the design of the small-scale s emiconductor probes, in terms of probe geometry, sensor placement, and aerodynamic performance. Derails are given of a range of wedge and py ramid semiconductor probes constructed, and the procedures used in cal ibrating and making measurements with them. Differences in performance are discussed, allowing the experimenter to choose an appropriate pro be for the particular measurement required. Finally, the application o f prototype semiconductor probes in a transient rotor experiment at HP turbine representative conditions is described, and the data so obtai ned are compared with CFD solutions of the unsteady viscous flow-field .