چكيده به لاتين
A prominent challenge in designing an axial compressor is to achieve the optimal performance, far from surge and stall Phenomena; but, maximum efficiency of compressor performance usually is associated with the onset of unsteadiness. Thus, Understanding this triggering mechanism is vital to the development of both active control and operability enhancement of the compression systems. It will also help designers to design compressors that are more robust to flow disturbances.One of the important methods of active control is air injection at rotor blade row tip region that is an effective way to increase the range of stability and even recover the compressor from the unstable condition.
Investigation of stall formation and its alleviation in a low-speed axial-flow compressor with the use of air injection at its rotor blade row tip is the main aim of this study. For this purpose several hot wire probes and a high response pressure transducer are used in data acquisition procedure and Twelve air injectors were mounted evenly spaced around the compressor casing upstream the rotor blade row. The results of these measurements using frequency analysis, including Fourier transform, short time Fourier transform and wavelet analysis, to describe the stall inception procedure and its fluctuation and stall recovery during air injection is presented. Using time-frequency analysis have an important role in detecting the stall phenomena and investigating the effect of air injection at rotor blade row tip region on elimination of the unsteadiness. The result shows that the stall inception process extends along blade whole span and the intensities of these fluctuations are much higher at the blade tip. Also, the observation indicates that air injection at the blade row tip enables this beneficial effects to extend throughout the blade whole span, especially while working at the near stall conditions. Circumferential Simultaneous measurements were carried out and according to results, Stall cell propagates with a circumferential speed lower than rotor wheel speed which is equal to 66% of rotational speed in this compressor. Finally, the effect of air injection parameters such as injection mass flow rate on eliminating unsteadiness was investigated.
