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Research Papers

Investigation of the Tip Clearance Flow in a Compressor Cascade Using a Novel Laser Measurement Technique With High Temporal Resolution

[+] Author and Article Information
Andreas Fischer1

Laboratory of Measurement andTesting Techniques,  Technische Universität Dresden, D-01062 Dresden, Germanyandreas.fischer2@tu-dresden.de

Lars Büttner

Laboratory of Measurement andTesting Techniques,  Technische Universität Dresden, D-01062 Dresden, Germanylars.buettner@tu-dresden.de

Jürgen Czarske

Laboratory of Measurement andTesting Techniques,  Technische Universität Dresden, D-01062 Dresden, Germanyjuergen.czarske@tu-dresden.de

Marcel Gottschall

 Institute of Fluid Mechanics, Technische Universität Dresden, D-01062 Dresden, Germanymarcel.gottschall@tu-dresden.de

Konrad Vogeler

 Institute of Fluid Mechanics, Technische Universität Dresden, D-01062 Dresden, Germanykonrad.vogeler@tu-dresden.de

Ronald Mailach

Chair of Thermal Turbomachinery,  Ruhr-Universität Bochum, D-44780 Bochum, Germanyronald.mailach@tu-dresden.de

1

Corresponding author.

J. Turbomach 134(5), 051004 (May 07, 2012) (9 pages) doi:10.1115/1.4004754 History: Received July 11, 2011; Revised July 22, 2011; Published May 07, 2012; Online May 07, 2012

The understanding of the tip clearance flow in axial compressors is a key issue for developing new compressors with enhanced efficiency and reduced noise for instance. However, necessary flow measurements in the blade tip region and within the tip clearance are challenging due to the small gap width. The application of a novel optical measurement technique named Doppler global velocimetry with laser frequency modulation is presented, which provides velocity field measurements of all three velocity components nonintrusively in the tip clearance flow of a linear cascade at near stall conditions. These array measurements have a high temporal resolution enabling turbulence analysis such as the evaluation of velocity standard deviations and turbulence spectra up to several kilohertz. Conventional pneumatic and hot-wire measurements in planes at the inlet and the outlet as well as on the blade surface were taken to complete the flow pattern and validate the data of the Doppler global velocimetry. Wake measurements identified a strong flow separation in the rear suction side dominating the transient character of the cascade flow. Towards the endwall this high loss region is reduced by the clearance flow and the resulting vortex, which is obviously not affected by the profile separation and the pulsating blockage frequency. Inside the blade passage and the tip clearance the Doppler global velocimetry measurements allowed a spatial assignment of the origin of the tip leakage flow and the downstream developing vortex. In addition, the tip clearance vortex could be resolved and identified successfully as the most dominant turbulence generating effect in the near endwall region at this high loading operating point of the blading.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Flow structure of the tip clearance vortex in an axial compressors blade row

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Figure 2

Scheme of cascade tunnel with reference frame

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Figure 3

Schematic setup of the FM-DGV technique for measuring one velocity component (fc laser center frequency, fD Doppler frequency, and cL light velocity)

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Figure 4

FM-DGV measurement arrangement in the linear cascade using three illumination directions i→1, i→2, i→3 and one observation direction o→ for three component measurements

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Figure 5

Power spectrum density (one-sided) of inflow axial velocity at (a) midspan and (b) near the endwall (HWA data acquired at 0.3l in front of cascade)

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Figure 6

Outlet steady state local axial velocity and flow angle distribution (upstream view, 5HP data acquired at 0.05l behind the cascade)

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Figure 7

Total pressure loss and streamwise vorticity distribution at outlet (upstream view, 5HP data acquired at 0.05l behind the cascade)

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Figure 8

RMS values of the local axial velocity and subtraction from mean values (upstream view, HWA data acquired at 0.05l behind the cascade)

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Figure 9

Power spectrum density (one-sided) of outlet axial velocity at (a) midspan and (b) near the endwall (HWA data acquired at 0.05l behind the cascade)

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Figure 10

Steady state profile pressure distributions (pressure tappings on blade surface)

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Figure 11

Mean velocity field of all three components of the tip leakage flow

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Figure 12

Velocity standard deviations σ1 , σ2 , σ3 of the three measured velocity components c1 , c2 , c3 along (o→-i→1), (o→-i→2), (o→-i→3),in the tip leakage flow (compare Fig. 4).

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Figure 13

Velocity power spectral density (PSD, one-sided) of the first measured velocity component at two sample positions (a) in the tip clearance and (b) in the tail of the TCV

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