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Research Papers: Gas Turbines: Structures and Dynamics

Blade Forcing Function and Aerodynamic Work Measurements in a High Speed Centrifugal Compressor With Inlet Distortion

[+] Author and Article Information
Albert Kammerer, Reza S. Abhari

Department of Mechanical and Process Engineering, Laboratory for Energy Conversion, ETH Zurich, 8092 Zurich, Switzerland

J. Eng. Gas Turbines Power 132(9), 092504 (Jun 21, 2010) (11 pages) doi:10.1115/1.4000614 History: Received July 23, 2009; Revised October 24, 2009; Published June 21, 2010; Online June 21, 2010

Centrifugal compressors operating at varying rotational speeds, such as in helicopters or turbochargers, can experience forced response failure modes. The response of the compressors can be triggered by aerodynamic flow nonuniformities such as with diffuser-impeller interaction or with inlet distortions. The work presented here addresses experimental investigations of forced response in centrifugal compressors with inlet distortions. This research is part of an ongoing effort to develop related experimental techniques and to provide data for validation of computational tools. In this work, measurements of blade surface pressure and aerodynamic work distribution were addressed. A series of pressure sensors were designed and installed on rotating impeller blades and simultaneous measurements with blade-mounted strain gauges were performed under engine representative conditions. To the best knowledge of the authors, this is the first publication, which presents comprehensive experimental unsteady pressure measurements during forced response, for high-speed radial compressors. The experimental data were obtained for both resonance and off-resonance conditions with uniquely tailored inlet distortion. This paper covers aspects relating to the design of fast response pressure sensors and their installation on thin impeller blades. Additionally, sensor properties are outlined with a focus on calibration and measurement uncertainty estimations. The second part of this paper presents unsteady pressure results taken for a number of inlet distortion cases. It will be shown that the intended excitation order due to inlet flow distortion is of comparable magnitude to the second and third harmonics, which are consistently observed in all measurements. Finally, an experimental method will be outlined that enables the measurement of aerodynamic work on the blade surface during resonant crossing. This approach quantifies the energy exchange between the blade and the flow in terms of cyclic work along the blade surface. The phase angle between the unsteady pressure and the blade movement will be shown to determine the direction of energy transfer.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Pressure sensor and impeller blade sensor installation: (a) pressure sensor size comparison, (b) sensor installation on suction side, and (c) sensor installation on pressure side

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Figure 2

Sensor location and coordinates: (a) sensor distribution and (b) coordinates

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Figure 3

Sensor gain dependence on temperature

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Figure 4

Sensor response spectrum from shock tube experiment

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Figure 5

Pressure sensor and strain gauge response to blade deformation during on-bench testing: the pressure sensor is affected by blade movement

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Figure 6

Arrangement and dimensions within the inlet section

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Figure 7

Campbell diagram for the main blade

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Figure 8

Measured total pressure distribution normalized with inlet static pressure (ptot/pinlet): (a) distortion screen not installed, (b) five lobe distortion screens installed, and (c) six lobe distortion screens installed

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Figure 9

Pressure excitation spectrum for two different screen configurations: data corresponds to sensor position 3, as shown in Fig. 2: (a) excitation spectrum for case without distortion screen, (b) excitation spectrum with five lobe screens, and (c) excitation spectrum with six lobe screens

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Figure 10

Unsteady pressure traces and amplitude of harmonic functions at 17,600 rpm near the stability limit (OL1): a distortion screen was not installed—(a) pressure traces on suction side, (b) pressure traces on pressure side, (c) unsteady pressure difference Δp/pinlet, (d) harmonic functions on suction side, (e) harmonic functions on pressure side, and (f) harmonics of forcing function

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Figure 11

Pressure and displacement for sensor 1 on the suction side, both sensors were mounted on blade 1: (a) pressure and (b) sensor displacement normal to surface

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Figure 12

Pressure and displacement for sensor 1 on the pressure side, both sensors were mounted on blade 4: (a) pressure and (b) sensor displacement normal to surface

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Figure 13

Displacement and pressure traces during resonance: (a) suction side sensor 1 mounted on blade 1 and (b) pressure side sensor 1 mounted on blade 4

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Figure 14

Phase and cyclic aerodynamic work on suction and pressure side for sensor position 1: (a) suction side sensor 1 installed on blade 1 and (b) pressure side sensor 1 installed on blade 4

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Figure 15

Cyclic aerodynamic work evolution for all available sensor positions on the suction and pressure sides (see Fig. 2): (a) suction side and (b) pressure side

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