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Research Papers

Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor—Part I: Particle Image Velocimetry

[+] Author and Article Information
M. Voges, R. Schnell, C. Willert, R. Mönig

 German Aerospace Center (DLR), Linder Höhe, 51147 Köln, Germany

M. W. Müller

 Technische Universität Darmstadt, Petersenstrasse 30, 64287 Darmstadt, Germany

C. Zscherp

 MTU Aero Engines, Dachauer Strasse 665, 80995 München, Germany

J. Turbomach 133(1), 011007 (Sep 09, 2010) (11 pages) doi:10.1115/1.4000489 History: Received August 27, 2008; Revised September 16, 2008; Published September 09, 2010; Online September 09, 2010

A single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per rotor pitch in order to investigate the predicted extension of the stall margin characteristics both numerically and experimentally. Contrary to most other studies, the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. Part I of this two-part contribution describes the experimental investigation of the blade tip interaction with casing treatment using particle image velocimetry (PIV). The nearly rectangular geometry of the CT cavities allowed a portion of it to be made of quartz glass with curvatures matching the casing. Thus, the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the rotor passage (87.5%, 95%, and 99%). For the outermost radial position, the light sheet probe was placed behind the rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the rotor blades. The chosen type of smoke-based seeding with very small particles (about 0.5μm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5×0.5mm2. The PIV database established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying computational fluid dynamics (CFD) calculations using the TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry, a better understanding of the complex flow characteristics can be achieved, as detailed in Part II of this paper.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

DTC stage with casing treatment

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Figure 2

Performance maps of the DTC. Markers point out operating conditions with PIV measurements for both CT and SW related to PE-ADP.

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Figure 3

Laser light sheet positions in relation to the blade height and compressor casing; configuration for (a) zrel=87.5% and 95% and (b) 99% blade height only

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Figure 4

Window support with glass bridge, light sheet probe positions, and clearance groove in the DTC casing; line (dot-dashed): axial reference y=0 mm for radial light sheet positions and perpendicular camera viewing direction; line (dashed): phase angle reference Φ=0 deg

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Figure 5

Photograph of the light sheet probe exit 1 and glass cavity area 2

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Figure 6

Pitchwise reconstruction of measured PIV velocity fields for the DTC with SW casing at 95% blade height for both PE-ADP and NS conditions at 100% rpm; (a) left side: axial velocity component u (shaded contour); (b) right side: circumferential velocity component v (shaded contour). All vectors give absolute velocity directions.

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Figure 7

Suction side view of the blade: contours give the SW CFD results of the axial (upper part) and circumferential (lower part) velocity distributions as well as shock configurations in the vicinity of the blade surface

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Figure 8

Measured velocity fields with CT at 100% rpm comparing peak efficiency (PE-ADP, left part, (a)–(c)) and near stall (NS, right part, (d)–(f)) conditions, illustrated for three rotor phase angles

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Figure 9

Velocity and vorticity distributions measured at zrel=95% and 65% rpm, comparing PE and NS operating conditions for two different phase angles

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Figure 10

Velocity and vorticity distributions measured at zrel=95% and 100% rpm, comparing PE-ADP and NS operating conditions for two different phase angles

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Figure 11

Phase angle sequence describing rotor movement by half a pitch, measured at zrel=99% for both 65% rpm (left, (a)–(c)) and 100% rpm (right, (d)–(f)), comparing PE and NS operating conditions for three different phase angles

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