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  • AIRCRAFT PROPULSION AND POWER  (2)
  • 1985-1989  (2)
  • 1925-1929
  • 1
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    Vortex shedding in compressor blade wakes (1987)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The wakes of highly loaded axial compressor blades were often considered to be turbulent, unstructured flows. Recent work has suggested that the blade wakes are in fact dominated by a vortex street-like structure. The work on the wake structure at MIT is reviewed, the results of a viscous numerical simulation are presented, the blade wake vortices are compared to those shed from a cylinder, and the implications of the wake structure on compressor performance are discussed. In particular, a two-dimensional, time accurate, viscous calculation shows both a periodic wake structure and time variations in the passage shock strength. The numerical calculations are compared to laser anemometer and high frequency response probe data. The effect of the wake structure on the entropy production and apparent adiabatic efficiency of the compressor rotor is discussed.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AGARD Transonic and Supersonic Phenomena in Turbomachines; 13 p
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Unsteady design-point flow phenomena in transonic compressors (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: High-frequency response probes which had previously been used exclusively in the MIT Blowndown Facility were successfully employed in two conventional steady state axial flow compressor facilities to investigate the unsteady flowfields of highly loaded transonic compressors at design point operation. Laser anemometry measurements taken simultaneously with the high response data were also analyzed. The time averaged high response data of static and total pressure agreed quite well with the conventional steady state instrumentation except for flow angle which showed a large spread in values at all radii regardless of the type of instrumentation used. In addition, the time resolved measurements confirmed earlier test results obtained in the MIT Blowdown Facility for the same compressor. The results of these tests have further revealed that the flowfields of highly loaded transonic compressors are heavily influenced by unsteady flow phenomena. The high response measurements exhibited large variations in the blade to blade flow and in the blade passage flow. The observed unsteadiness in the blade wakes is explained in terms of the rotor blades' shed vorticity in periodic vortex streets. The wakes were modeled as two-dimensional vortex streets with finite size cores. The model fit the data quite well as it was able to reproduce the average wake shape and bi-modal probability density distributions seen in the laser anemometry data. The presence of vortex streets in the blade wakes also explains the large blade to blade fluctuations seen by the high response probes which is simply due to the intermittent sampling of the vortex street as it is swept past a stationary probe.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-176879 , NAS 1.26:176879
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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