چكيده به لاتين
One of challenges in designing of axial compressors is to achieve the optimal performance, far from unstable phenomena; but, maximum efficiency of compressor performance usually is associated with the onset of instability and the occurrence of phenomena such as surge and stall. The presence of tip leakage in the axial compressor causes the formation of tip leakage vortex. The intense interaction between the tip leakage vortex and flow passage cause the compressor`s efficiency to losses. Therefore, the study of controlling and reducing the undesirable effects of an axial compressor blade row tip leakage flow is important. In order to identify the mechanism of instability, the ability to detect disturbance occurring in the pre-stall process and further, is a precise understanding of stall`s formation structure, is of particular importance. The use of precision measuring equipment is a useful tool for achieving this information. In this research, a brief description of the types of instability in axial compressors, the cause and formation of instability, as well as their control methods have been discussed. The main axis of the research, is to study the formation of rotating stall in a low speed axial compressor. For this purpose, laboratory measurement and numerical simulation have been used to achieve a comprehensive and precise understanding of the process before the stall inception, its formation and development. The data acquisition in the laboratory section was carried out with the use of instantaneous Honeywell pressure sensors. An array of 30 pressure sensors on the compressor casing it covers a blade passage (30 degree from the compressor circumference). Results are presented in the form of row signals, instantaneous static pressure contour and also in the form of frequency analysis including Fourier transform, short time Fourier transform. By examining the results of instantaneous pressure contours, it was found that the spike stall process involves flow separation from the blade leading edge and subsequently forming the spike vortex. The formation of spike vortex in the flow passage leads to significant blockage in the main flow. The results of fluctuation signal show that, during the stall formation process, the Fourier transform can be able to show the dominant frequencies and identify aerodynamic phenomena in the flow field. In parallel to laboratory actives, numerical simulations of the flow field have also been used. The obtمain information is used to compare the results of experimental to verify the numerical method and to find more flow details.
