Development and Application of a Concentration Probe for Mixing Flows Tracking in Turbomachinery Applications

Abstract

Modern gas turbines present important temperature distortions in the core-engine flowpath, mainly in the form of hot and cold streaks imputed to combustor burners and components cooling systems. As they highly influence turbines performance and lifetime, the precise knowledge of the thermal field evolution through the combustor and the high-pressure turbine is fundamental. The majority of the past studies investigated streak migrations directly examining the thermal field, while a limited amount of experimental work employed approaches based on the detection of tracer gases. The latter approach provides a more detailed evaluation of the evolution and mixing of the different flows. However, the slow time response due to the employment of sampling probes and gas analyzers make the investigation of a whole measurement plane extremely time consuming. To tackle this issue, in this study, a commercial oxygen sensor element and its excitation/detection unit were integrated into a newly developed probe to carry out local tracer gas concentration measurements exploiting the fluorescence behavior. The probe was provided with a Kiel-like shield, a pressure port, and a thermocouple, to correct the readings in case of 3D flows with pressure, temperature, and velocity gradients. This article summarizes the probe development and calibration activities, with the characterization of its accuracy for different flow conditions. Finally, two probe applications are described: first, the probe was used to detect tracer gas concentrations on a jet flow

afterward, it was traversed on the interface plane between a nonreactive, lean combustor simulator, and the NGV cascade. The probe has proven to provide accurate and reliable measurements from both a quantitative and qualitative point of view even in highly 3D flow fields typical of gas turbines conditions.