Influence of blade row aerodynamics on pneumatic gas turbine instrumentation

Abstract

Steady state, inter row measurements in multistage axial compressors are relevant to the current design process. The objective in obtaining such data is for evaluation of compressor blading as well as validation for the computer programmes used in compressor design. Multi-hole pressure probes are a reliable and economical method of collecting detailed flowfield data in compressors for these purposes. These probes are calibrated in a uniform flow in a wind tunnel prior to use, to determine their response to a range of flow angles and speeds. When the probe is subsequently used for measurements in the compressor, often the small inter row spacing means that the probe has to be close to the downstream stator passage and upstream rotor. The result is that the probe is no longer situated in the uniform flow in which it was calibrated, in terms of influences from both the upstream rotor and downstream stator. This project presents the investigation of these two effects on steady state pressure probe measurements. The effects of blockage on a probe positioned in front of a stator row in a high speed compressor were studied using CFD. This was also carried out on a large scale probe in a low speed compressor. It was found that the blockage effect caused a reduced mass flow in the downstream stator passage which in turn lead to an altered flow angle and a small reduction in measured total pressure. Experimental in rig calibrations showed that the change in flow angle was due to an angular offset of the pressure distribution about the probe. These calibrations also showed that the wind tunnel calibration was valid in the compressor within a small angular range. The influence of the upstream rotor passing was studied using an unsteady CFD model. Responses of the individual probe ports and the deduced flow angle and total pressure indicated that the steady state blockage effect is present throughout the wake passing. The wake passing was found to be a largely two dimensional effect in that the radial flow component changes in the low speed compressor wakes had little influence. The Total Technology thesis incorporates a management project on the relevant topic of project selection within companies. An existing project selection model was applied to a sample group of projects to determine the applicability of such models. The main findings were that these models can generate useful information for further selection decisions and that the applicability is towards lower budget projects where a structured approach is often not used.