Final work : Investigation of Reynolds Number Effects on Performance and Throughflow Modelling of Low-Pressure Compressors

Abstract

The performances of a compressor operated in flight conditions differ from what is observed on the ground. One of the main reasons is associated to the variation of inlet Reynolds number. Usually, the design of a new compressor is performed assuming ground conditions (high Re). The performances in flight conditions (low Re) are then estimated by correcting the performances on the ground with an estimation of the Reynolds effects. This work aims at investigating the Reynolds effects on the performances of a high-speed low-pressure compressor and at providing modification guidelines for a throughflow model such that, starting from a throughflow model established for high Reynolds number, with these modifications, the performances at low Reynolds number can be estimated. Two values of Reynolds number have been studied in the present work. High Re conditions refer to a Reynolds Number Index (RNI) of 1 while low Re conditions refer to RNI = 0.45. First, two-dimensional losses are computed for each blade row. It is found that the Reynolds number has minimal effects on the shape of the loss characteristics but it affects the mean level of losses. Then the throughflow model for low Re conditions was created. As a first approximation, the set of correlations was taken from an already existing throughflow model established for high Re conditions. After comparison of the results with experimental data at the same Re level, it was concluded that the correlations from the high Re model could not represent the performances at low Re accurately. A modification of the parameters from the correlations was then proposed. It was found that a modification of the minimal loss incidence is sufficient to provide accurate results.