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Research Papers

Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor—Part II: Numerical Results

[+] Author and Article Information
R. Schnell, M. Voges, 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), 011008 (Sep 09, 2010) (11 pages) doi:10.1115/1.4000490 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 consisting of 3.5 axial slots per rotor pitch in order to investigate its influence on stall margin characteristics, as well as on the rotor near tip flow field, both numerically and experimentally. Contrary to most other studies, a generic casing treatment (CT) was designed to provide optimal optical access in the immediate vicinity of the CT, rather than for maximum benefit in terms of stall margin extension. The second part of this two-part paper deals with the numerical developments and their validation, carried out in order to efficiently perform time-accurate casing treatment simulations. The numerical developments focus on the extension of an existing coupling algorithm in order to carry out unsteady calculations with any exterior geometry coupled to the main flow passage (in this case a single slot), having an arbitrary pitch. This extension is done by incorporating frequency domain, phase-lagged boundary conditions into this coupling procedure. Whereas the phase lag approach itself is well established and validated for standard rotor-stator calculations, its application to casing treatment simulations is new. Its capabilities and validation will be demonstrated on the given compressor configuration, making extensive use of the detailed particle image velocimetry flow field measurements near the rotor tip. Instantaneous data at all measurement planes will be compared for different rotor positions with respect to the stationary slots in order to evaluate the time-dependent interaction between the rotor and the casing treatment.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Transonic compressor stage equipped with casing treatment

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Figure 8

Contours of circumferentially averaged density amplitudes from the unsteady stage calculation: second harmonic (mainly slot influence)—values below amp{ρ}<0.01 kg m−3 are blanked (58 slot case)

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Figure 9

Contours of circumferentially averaged density amplitudes from the full unsteady calculation: first harmonic (mainly stator upstream influence); values below amp{ρ}<0.01 kg m−3 are blanked (58 slot case)

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Figure 10

Isosurfaces of λ2-criterion for an operating point at peak efficiency (100% rpm) and near-tip streamlines; contours show static pressure at a constant axial position; all flow quantities are time averaged

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Figure 11

Isosurfaces of λ2-criterion for a near stall operating point (100% rpm) and near-tip streamlines; contours show static pressure at a constant axial position; all flow quantities are time averaged

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Figure 16

Comparison of velocity data extracted along a constant axial position (x=10 mm, dashed line in Fig. 1)—peak efficiency conditions, measurement plane zrel=87%, rotor position Φ=0 deg

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Figure 18

Comparison of velocity data extracted along a constant axial position (x=10 mm, dashed line in Fig. 1)—peak efficiency conditions, measurement plane zrel=95%, and rotor position Φ=0 deg

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Figure 19

Measured velocity components u, v (m/s) in comparison with the numerical results (near stall, zrel=87%)

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Figure 14

Shock system(s) near the casing (rrel≈90%) with (left, time average data) and without CT (right) for a near stall operating point—the black rectangle sketches the area inside which PIV data was obtained (Figs.  15161718192122)

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Figure 7

Contours of circumferentially averaged density amplitudes: first-slot-harmonic from rotor point of view-values below amp{ρ}<0.01 kg m−3 are blanked (64 slot case)

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Figure 6

Contours of density amplitudes in a meridional plane (first-slot-harmonic from rotor point of view), circ. averaged; the dashed lines denote the PIV measurement planes—values below amp{ρ}<0.01 kg m−3 are blanked

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Figure 5

Contours of the pressure amplitude (first BPF) in the blade tip region for the single slot case with phase-lagged boundary conditions

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Figure 4

Contours of the pressure amplitude (first BPF) in the blade tip region for the multislot periodic case

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Figure 3

Rotor entry and exit mass flow (nondimensionalized by the time mean, top) and slot mass flow (bottom)

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Figure 2

Computational grid of the compressor stage with 1.6 million nodes (left) and grid detail in the rotor tip region with casing treatment block (right)—flow passages are duplicated for a better view only

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Figure 22

Measured velocity components u, v (m/s) in comparison with the numerical results (near stall, zrel=99%—tip gap)

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Figure 21

Measured velocity components u, v (m/s) in comparison with the numerical results (near stall, zrel=95%)

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Figure 20

Comparison of velocity data extracted along a constant axial position (x=10 mm, dashed line in Fig. 1)—near stall conditions, measurement plane zrel=87%, and rotor position Φ=180 deg

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Figure 17

Measured velocity components u, v (m/s) in comparison with the numerical results (peak efficiency, zrel=95%)

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Figure 15

Measured velocity components u, v (m/s) in comparison with the numerical results (peak efficiency, zrel=87%)

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Figure 13

Rotor suction side static pressure and near surface streamlines for a near stall operating point

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Figure 12

Time-averaged flow field in terms of flow vectors and streamlines inside the slot at peak efficiency; the “radial” inflow to the slot is indicated by positive w-velocities in the rear part; slices at constant axial positions are contoured with axial velocity; all velocities in (m/s)

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