Abstract
ABSTRACTSteps required for proper acquisition and processing of laser Doppler velocimetry data for turbomachinery research applications are addressed. Turbomachinery applications are difficult due to the small internal passages, high-frequency fluctuations, large turbulence intensities, and strong secondary flows resulting in low overall signal-to-noise ratios and narrowband noise sources that cannot be removed by simple band-pass filters. Special aspects that must be considered for successful and accurate laser Doppler velocimetry studies to be conducted in turbomachinery are discussed. Specifically, the design of the measurement volume size, reflection mitigation, engineering of seed particle size and injection schema, and alignment of the traverse mechanism are addressed in terms of their importance (from literature sources) and the solutions implemented by the authors. These techniques have been applied to successfully obtain three-component, unsteady velocity data in a high-speed centrifugal compressor for aeroengine application. Processing techniques are also presented including a novel mixture-model-based statistical method for narrowband noise isolation developed by the authors. The method, validation steps, and example results are presented, showing the successful rejection of noise with high accuracy, a low failure rate, and a significant reduction in required manual inspection. This newly developed method elucidated flow features that were not clear prior to the noise removal.
Highlights
Growing concerns regarding environmental change and rising fuel costs have forced gasturbine engine manufacturers to place unprecedented value on reducing fuel burn
A 99% confidence interval on the true proportion of false negatives yields an upper bound of 1.3%. These results show that the method correctly identifies results that need further study
The detailed flow field resulting from this experimental study will be presented in a future paper; the following figures present a small sample of the obtained data
Summary
Growing concerns regarding environmental change and rising fuel costs have forced gasturbine engine manufacturers to place unprecedented value on reducing fuel burn. This drives engines toward higher overall pressure ratios to increase thermal efficiency and smaller core sizes to obtain greater bypass ratios for improved propulsive efficiency. Small core axial compressors suffer a loss in efficiency due to the increased prevalence of endwall flow effects in the narrow passage. In such a flow regime, a centrifugal compressor stage is a potential alternative due to its decreased sensitivity to geometric deviations and endwall effects[1]. Existing computational fluid dynamics (CFD) and empirical models are still relied upon in the design of novel compressor stages
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