Abstract
Tip clearance flow in axial flow compressor is unavoidable and responsible for pressure losses and noise generation and influences the stability of the compressor. However, necessary flow measurement in the blade tip region is a great challenge due to the small gap width as well as the structure limitation. In this paper, a polyvinylidene fluoride (PVDF) piezoelectric-film sensor array is developed to capture the dynamic pressure field over the blade tip in an axial flow compressor. The PVDF sensor array with 40 evenly distributed sensing points is fabricated directly on a 30 μm thick aluminum-metalized polarized PVDF film through photolithography. Dynamic calibration of the sensor is accomplished using acoustic source as excitation and a microphone as a reference. The test pressure range is up to 3.5 kPa and the sampling frequency is 20 kHz. The sensor presents a high signal-to-noise ratio and good consistency with the reference microphone. Sensitivity, frequency response, linearity, hysteresis, repeatability as well as the influence of temperature are also investigated through the calibration apparatus. The calibration gives credence to the relevance and reliability of this sensor for the application in dynamic pressure field measurement. The sensor is then applied to an actual measurement in a compressor. The output of the PVDF sensor array is also compared with the results of common pressure transducers, and the features of the dynamic pressure filed are discussed. The results indicate that the PVDF sensor array is capable of the dynamic pressure field measurement over the blade tip, and superior to the conventional approaches in installation, spatial resolution, frequency response, and cost. These advantages indicate its potential broad application in pressure measurement, especially for the complex spatial surface or thin-walled structure, such as the blade surface and the thin casing wall of the compressor.
Highlights
Tip clearance flow in axial flow compressor is an unavoidable flow induced by the relative motion of the blade tip and the casing
Temperature was gradually increasing with speed, so it was necessary to research the influence of temperature on the polyvinylidene fluoride (PVDF) sensor
In order to validate the effectiveness of the PVDF sensor array, single sensing point results are compared with Kulite transducers in the time domain and frequency domain
Summary
Tip clearance flow in axial flow compressor is an unavoidable flow induced by the relative motion of the blade tip and the casing. A set of high-response pressure transducers, which are arranged in a line [10,11,12,13] or an array [14,15] on the casing wall over the rotor blade tip, are widely used in tip clearance flow measurement. It is necessary to develop a pressure sensor for dynamic pressure field measurement, which needs to fulfill the following requirements: high spatial and temporal resolution, easy install, a wide pressure range, small response time, low cost and have little effect on the compressor structure as well as the flow field. An effective, easy installation, high-resolution, and low-cost PVDF sensor array is developed to capture the dynamic pressure field over the blade tip in an axial flow compressor. The dynamic pressure field is measured by the sensor, and the features of the dynamic pressure filed are discussed
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