Studies Of End Wall Effects On Rotating Stall Inception In Axial Compressors

Author : Benjamin P. Johnson
Publisher :
ISBN 13 :
Total Pages : 120 pages
Book Rating : 4.:/5 (256 download)

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Download or read book Observed Flow Characteristics of Rotating Stall Inception and Its Prevention Using Discrete Tip Injection in the NASA Stage 35 Axial Compressor with New Analysis Methods written by Benjamin P. Johnson and published by . This book was released on 2008 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: In order to further our understanding of the effects of tip injection in preventing rotating stall, a number of computational cases were run which modeled stall inception in the NASA compressor Stage 35. The flow solver TURBO, written and developed by Dr. Jen-Ping Chen, was used and new post-processing analysis methods were implemented in these cases. These include the investigation of three-dimensional disturbance (zero axial velocity) pockets, diffusion factor analyses, angle of attack analyses, and negative axial velocity volume measurements. The utilization of these methods led to a number of observations. The first was that the three-dimensional disturbances were first formed in the mid-span of the rotor passages and then migrated to the tip region. Secondly, in both the stable and unstable cases, the disturbances travelled at 100% rotor speed around the annulus upon their inception. The third observation made was that, in stalling cases, the disturbances would eventually occupy the entire breadth of a rotor passage in the vicinity of the tip. Upon this occurrence, the disturbance would begin to propagate upstream of the leading edge of the rotor blade. It would then migrate around the rotor leading edge, merging with the disturbances in the adjacent passages while slowing to approximately 50% rotor speed. The diffusion factor and angle of attack analyses proved less conclusive than had been hoped in providing a definitive, quantitative indication of the inevitability of stall. The original hope was that one or both of these parameters would prove to be a reliable, definitive indicator of the inevitable onset of stall at a given throttle. The diffusion factor analysis provided a means to indicate qualitative differences between different cases, i.e. indicating whether one case is more likely to stall than another. The angle of attack analysis, for the most part, seemed to accurately reflect the actual flow conditions - high angles of attack were recorded for blades which exhibited leading-edge flow separation. Two cases were chosen to represent a stable and stalling case. The results of the stable case indicate that the tip injectors maintain stability in the compressor by preventing the formation of disturbances which occupy the full breadth of a given rotor passage. As the disturbances migrated toward the tip, the injectors would wash them away. To maintain stable operation, some disturbances required passage through the influence of only one injector, while in other cases passage through multiple injectors was required. The results of the unsteady case indicate that if the amount of injection is insufficient, the subsequent merging and growth of the disturbances blocks a significant portion of the rotor face and prevents sufficient mass flow from getting through, resulting in rotating stall.