Summary There is no general rule in the literature to help choose a correct flow control device for any given case of turbomachinery applications. This suggests individual optimization of flow control devices for each specific case. The objective of this study is to prove experimentally the benefits of passive control methods in improving the compressor performance. This allows to reduce the fuel consumption, leading to energy saving and reduction of atmospheric pollution. Two features have been controlled in this study: flow separation over the blade surfaces and the secondary flow over the cascade endwalls. Vortex generator ribs are tested on the blade suction side for flow reattachment on the blade surfaces, and low‐profile vortex generators are tested on the side walls of the compressor cascade against secondary flow losses. Different vortex generator designs are compared for total pressure recovery, flow turning, boundary layer characteristics, and pressure distributions over the endwalls. Copyright © 2016 John Wiley & Sons, Ltd.
A single-hole probe was designed to measure steady and periodic flows with high fluctuation amplitudes and with minimal flow intrusion. Because of its high aspect ratio, estimations showed that the probe resonates at a frequency two orders of magnitude lower than the fast response sensor cut-off frequencies. The high fluctuation amplitudes cause a non-linear behavior of the probe and available models are neither adequate for a quantitative estimation of the resonating frequencies nor for predicting the system damping. Instead, a non-linear data correction procedure based on individual transfer functions defined for each harmonic contribution is introduced for pneumatic probes that allows to extend their operating range beyond the resonating frequencies and linear dynamics. This data correction procedure was assessed on a miniature single-hole probe of 0.35 mm inner diameter which was designed to measure flow speed and direction. For the reliable use of such a probe in periodic flows, its frequency response was reproduced with a siren disk, which allows exciting the probe up to 10 kHz with peak-to-peak amplitudes ranging between 20%–170% of the absolute mean pressure. The effect of the probe interior design on the phase lag and amplitude distortion in periodic flow measurements was investigated on probes with similar inner diameters and different lengths or similar aspect ratios (L/D) and different total interior volumes. The results suggest that while the tube length consistently sets the resonance frequency, the internal total volume affects the non-linear dynamic response in terms of varying gain functions. A detailed analysis of the introduced calibration methodology shows that the goodness of the reconstructed data compared to the reference data is above 75% for fundamental frequencies up to twice the probe resonance frequency. The results clearly suggest that the introduced procedure is adequate to capture non-linear pneumatic probe dynamics and to reproduce time-resolved data far above probe resonant frequency.
This article presents a Siren Disk proof of concept for the dynamic excitation of pressure probes, and a method to reconstruct distorted signals due to pneumatic channels. Constraints in sensor installation require placing a pressure transducer distant from the measurement point. The transducer is usually connected through a pneumatic channelcreating a probe, which alter its dynamic response. The Siren Disk is used for the identification of transfer functions of different pressure probe geometries. The device is capable of producing pressure signals up to 10 kHz and 3.5 bara (peak-to-peak = 2.5 bars). The transfer function is obtained through the comparison of the probe signal to a flush mounted reference transducer that is subjected to the same pressure signal. The response of the probes was shown to be highly non-linear. Hence, a multi-dimensional transfer function is developed for the system identification of the probes. The function is based on the Fourier series, and consists of a set of sub transfer functions describing the average gain and phase lag for the offset and the harmonics. The approach is well suited to capture the non-linear frequency response of complex sensor installations. Experiments show that the flat response of transducers is jeopardized by the introduction of the low pass filter behavior from the pneumatic channels. The probe's signal was significantly distorted compared to the reference signal. The inverse transfer function is used to reconstruct the probe's signal in the time domain. Good agreement is found between the reconstructed and the reference signals even at excitation frequencies beyond the probe's resonant frequency. Hence, highlighting a wide range of validity for the proposed method.
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