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Research Papers

On the Unsteady Formation of Secondary Flow Inside a Rotating Turbine Blade Passage

[+] Author and Article Information
C. M. Schneider

Institute of Aircraft Propulsion Systems (ILA),
Pfaffenwaldring 6,
Stuttgart 70569, Germany
e-mail: schneider@ila.uni-stuttgart.de

D. Schrack, M. Kuerner, M. G. Rose, S. Staudacher

Institute of Aircraft Propulsion Systems (ILA),
Pfaffenwaldring 6,
Stuttgart 70569, Germany

Y. Guendogdu, U. Freygang

MTU Aero Engines AG,
Dachauer Strasse 665,
Munich 80995, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 3, 2013; final manuscript received July 17, 2013; published online November 8, 2013. Editor: Ronald Bunker.

J. Turbomach 136(6), 061004 (Nov 08, 2013) (10 pages) Paper No: TURBO-13-1133; doi: 10.1115/1.4025582 History: Received July 03, 2013; Revised July 17, 2013

This paper addresses the unsteady formation of secondary flow structures inside a turbine rotor passage. The first stage of a two-stage, low-pressure turbine is investigated at a Reynolds Number of 75,000. The design represents the third and the fourth stages of an engine-representative, low-pressure turbine. The flow field inside the rotor passage is discussed in the relative frame of reference using the streamwise vorticity. A multistage unsteady Reynolds-averaged Navier–Stokes (URANS) prediction provides the time-resolved data set required. It is supported by steady and unsteady area traverse data acquired with five-hole probes and dual-film probes at rotor inlet and exit. The unsteady analysis reveals a nonclassical secondary flow field inside the rotor passage of this turbine. The secondary flow field is dominated by flow structures related to the upstream nozzle guide vane. The interaction processes at hub and casing appear to be mirror images and have characteristic forms in time and space. Distinct loss zones are identified, which are associated with vane-rotor interaction processes. The distribution of the measured isentropic stage efficiency at rotor exit is shown, which is reduced significantly by the secondary flow structures discussed. Their impacts on the steady as well as on the unsteady angle characteristics at rotor exit are presented to address the influences on the inlet conditions of the downstream nozzle guide vane. It is concluded that URANS should improve the optimization of rotor geometry and rotor loss can be controlled, to a degree, by nozzle guide vane (NGV) design.

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References

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Figures

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Fig. 1

Cascade end wall flow structure reported by Sharma and Butler [2]

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Fig. 2

Schematic of the ATRD-Rig; traverse planes as dotted lines

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Fig. 3

Five-hole probe with thermocouple (a) and dual-film probe (b) in front of vane segments

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Fig. 4

Coordinate systems applied: (1) cylindrical rig coordinate system; (2) streamwise-aligned coordinate system

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Fig. 5

Measured (5hp) (a) and predicted (b) streamwise vorticity ωs at rotor inlet in the absolute frame of reference

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Fig. 6

Measured (5hp) (a) and predicted (b) streamwise vorticity ωs at rotor exit in the absolute frame of reference

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Fig. 7

Isosurfaces of streamwise vorticity ωs inside the rotor passage at hub in the relative frame of reference with isosurface levels of –6, –4, –2, 2, 4, and 6; (a) t/T = 3/16; (b) t/T = 12/16; (c) t/T = 19/16; (d) t/T = 25/16

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Fig. 8

Isosurfaces of streamwise vorticity ωs inside the rotor passage at casing in the relative frame of reference; (a) t/T = 5/16, isosurface levels of ±1.5, ±3.0, and ±4.5; (b) t/T = 26/16, isosurface levels of −2.5, −3.0, −3.5, 1.0, 2.0, and 3.0

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Fig. 9

Measured isentropic stage efficiency ηis at rotor exit in the absolute frame of reference

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Fig. 10

Flow fields inside the rotor passage in the relative frame of reference predicted by URANS and RANS; (a) unsteady, time-averaged (URANS); (b) steady (RANS)

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Fig. 11

Predicted flow field at axial position x/c = 0.6 inside the rotor passage at time step t/T = 19/16 in the relative frame of reference; black lines: streamwise vorticity ωs (Δωs = 1.0); contours: viscous dissipation δ

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Fig. 12

Unsteady data in the absolute frame of reference measured by the dual-film probe; contours: ensemble-averaged absolute circumferential angle e(α); white solid lines: ensemble-averaged periodic fluctuations of absolute Mach number σp(Ma), line interval Δσp(Ma) = 0.005; (a) t/T = 0; (b) t/T = 3/16; (c) t/T = 6/16; (d) t/T = 9/16; (e) t/T = 12/16; (f) t/T = 15/16

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Fig. 13

Circumferentially mass-averaged absolute circumferential angle α at rotor exit

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