Turbulence Measurements in Axial Turbines Using Fast Response Aerodynamic Pressure Probes

Abstract

Abstract Improving the comprehension of turbomachinery fluid-dynamics is vital to increase their performance, and calls for the development or extension of advanced instrumentation. In this context, novel data acquisition and data reduction techniques have been recently developed at Politecnico di Milano for turbulence measurements performed with Fast-Response Aerodynamic Pressure Probes. These improvements address a gap in the capabilities of such probes, as turbulence data were among the few, yet very important, information they could provide only on a quality level. At first, the technique is validated against hot-wire measurements on a low-speed wind tunnel, where a combustor simulator is inserted with or without an upstream turbulence grid generator. Second, the developed methodology is applied downstream of both the stator and the rotor of a single-stage axial turbine, where the probe robustness and reliability are fully exploited to gain crucial flow information also in a harsh flow environment, where the use of hot wires might be critical. In this paper, the measured turbulence intensity using FRAPP is compared among three different operating conditions obtained by changing the rotor rotational speed. Furthermore, the paper explores the impact of non-uniform stage inlet conditions, that resemble the combustor outlet disturbances, on the stator and rotor flow features. The regions with the highest turbulence levels are observed in areas characterized by secondary flows, wakes, end-walls, and the residual swirl profile. The stator-rotor interaction contributes to the turbulence generation both downstream of the stator and the rotor. Additionally, an increase in blade loading corresponds to higher intensity in secondary flows, leading to elevated turbulence levels at the rotor exit. The injection of combustor non-uniformities has a diminished impact as the rotor load increases, given that the flow field becomes predominantly influenced by strong secondary flows.