RESEARCH ON THE UNSTEADY FLOW IN AN AXIAL FLOW COMPRESSOR ROTOR BASED ON PVDF PIEZOELECTRIC-FILM SENSOR ARRAY

摘要

The unsteady flow in an axial flow compressor rotor is responsible for noise generation and unexpected excitation of blade vibration; therefore, compressors may suffer from fatigue failure of blades and eventually become unable to operate. At present, a set of Kulite pressure transducers mounted on the casing wall is widely used to acquire the pressure field of unsteady flow. However, it will affect the compressor structure and it is physically impossible to mount at a small spacing to capture the variation of casing wall pressure precisely because of the size of transducers. For the requirement of measurement, a self-developed PVDF (polyvinylidene fluoride) piezoelectric-film sensor array measurement system was applied to measure and capture the pressure field distribution over the compressor rotor blade tip clearance. In this system, a multi-measuring points PVDF array, in which 40 measuring points was contained in a 70mm by 40mm rectangle area, was attached on the casing wall of the rotor blade tip. This new technique has great advantages over traditional measurement technique, such as wide frequency response, high space resolution, less impact on the compressor, easy installation and so on. Based on a multistage axial compressor rig test, the unsteady flow pattern on the casing wall was well captured by the PVDF array. And it is revealed in all measuring points that the resonance occurs all over the compressor is under one single frequency, and the pressure level of the acoustic resonance exceeds the level of the usually dominated blade passing frequency when close to the stability limit. At the same time, the acoustic resonance will be modulated with the blade passing frequency.