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Research Papers

On the Phenomenon of Pressure Pulses Reflecting Between Blades of Adjacent Blade Rows of Turbomachines

[+] Author and Article Information
Jerzy A. Owczarek

Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA 18015

J. Turbomach 133(2), 021016 (Oct 22, 2010) (11 pages) doi:10.1115/1.4001185 History: Received July 23, 2009; Revised July 27, 2009; Published October 22, 2010; Online October 22, 2010

The recently revived interest in “acoustic resonances,” whose details are still not well defined or understood, points to a realization that a new look at some previously unrecognized findings is needed to explain problems encountered in operation of compressors and turbines. The purpose of this paper is to call the attention of the turbomachinery community to an important physical phenomenon of pressure waves in form of pulses, which reflect between blades of adjacent blade rows of turbomachines discovered more than 40 years ago, about whose existence and consequences there is little awareness today. The turbine test results which led the author in 1957 to hypothesize the existence of the phenomenon of reflecting pressure pulses are described. Subsequently, his 1966 ASME paper is discussed. In it, the author reported on the photographed observations of pressure pulses reflecting between stationary nozzles and moving blades of a water-table turbine at Lehigh University, on the description of the various types of such waves, and on an explanation of some of the resonant blade excitation frequencies observed by National Advisory Committee for Aeronautics (NACA) in a turbine of turbojet engine. This is followed by a description of his 1984 ASME paper, in which more general formulae were derived for the blade excitation frequencies caused by the reflections of pressure pulses between the rotor blades, and both upstream and downstream stator vanes. These equations were subsequently used to explain the blade excitation frequencies measured in an axial compressor stage. Finally, his 1992 AIAA paper is discussed, in which additional formulae relating to the reflecting pressure pulses were derived, and the process of formation of a pressure pulse was explained. To put this work in perspective, the author provided, in mostly chronological order, excerpts from reports on operational problems encountered with turbomachines in service and brief descriptions, from selected publications, of pertinent research work.

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References

Figures

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Figure 1

Single-stage air turbine efficiency test results (1957) (3)

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Figure 2

Single-stage steam turbine efficiency test result (1930s) (3)

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Figure 3

Path of a single-reflection backward-running wave, which spans one nozzle spacing (wave (1W×1N)B) (1)

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Figure 4

NACA turbine blade vibration test result (adapted from Ref. 4; spacing between blades: 075 in.)

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Figure 5

(a) A sequence of photographs of a pressure pulse moving toward a nozzle (1,3) (b) Positions of pressure pulses shown in Fig. 5. Numbers near the pressure pulses correspond to photograph numbers.

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Figure 6

A pressure pulse moving toward a turbine blade (1,3)

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Figure 7

A pressure pulse moving toward a nozzle (1,3)

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Figure 8

Two pressure pulses reflecting from a nozzle (1,3)

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Figure 9

Wave resonance diagram for the waves reflecting from the upstream stator vanes (full symbols denote the onset of vibration; open symbols denote the test points (2))

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Figure 10

Wave resonance diagram for waves reflecting from the downstream stator vanes (full symbols denote the onset of vibration; open symbols denote the test points (2))

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Figure 11

Flow velocity triangles in space between the stator nozzles and rotor blades (3)

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Figure 12

Formation of a forward-running pressure pulse (1,3)

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