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Research Papers

Identification of Spinning Mode in the Unsteady Flow Field of a Low Pressure Turbine

[+] Author and Article Information
Davide Lengani, Andreas Marn

Institute for Thermal Turbomachinery and Machine Dynamics,  Graz University of Technology, Graz 8010, Austria

Berardo Paradiso1

Institute for Thermal Turbomachinery and Machine Dynamics,  Graz University of Technology, Graz 8010, Austria

Emil Göttlich

Institute for Thermal Turbomachinery and Machine Dynamics,  Graz University of Technology, Graz 8010, Austriadavide.lengani@tugraz.at

1

Currently affiliated with Dipartimento di Energia, Politecnico di Milano, Milano, Italy.

J. Turbomach 134(5), 051032 (May 31, 2012) (8 pages) doi:10.1115/1.4004875 History: Received July 12, 2011; Revised August 04, 2011; Published May 31, 2012; Online May 31, 2012

This paper presents an experimental investigation of the vane-blade unsteady interaction in an unshrouded low pressure (LP) turbine research rig with uneven blade/vane count (72 blades and 96 vanes). The rig was designed in cooperation with MTU Aero Engines and considerable efforts were put on the adjustment of all relevant model parameters. In particular blade count ratio, airfoil aspect ratio, reduced mass flow, reduced speed, and Mach and Reynolds numbers were chosen to reproduce the full scale LP turbine at take off condition. Measurements by means of a fast-response pressure probe were performed adopting a phase-locked acquisition technique in order to provide the time resolved flow field downstream of the turbine rotor. The probe has been fully traversed both in circumferential and radial traverses. The rotor exit is characterized by strong perturbations due to the tip leakage vortex and the rotor blade wake. Circumferential nonuniformities due to the upstream vane wake and to the downstream exit guide vane potential effects are also identified. Furthermore, in the present configuration with an uneven blade/vane count the nonuniformities due to the stator and rotor row are misaligned along the whole turbine circumference and create a spinning mode that rotates in direction opposite to the rotor at a high frequency. The aeroacoustic theory is employed to explain such further unsteady pattern. The variations of the exit flow angle within a cycle of such pattern are not negligible and almost comparable to the ones within the blade passing period.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 3

Time snapshot of the relative Mach number; the dominant structures of the flow are marked over the experimental results

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Figure 4

Time-resolved distribution of the relative Mach number

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Figure 5

Space-time plot of the relative Mach number. A, B, C correspond to the regions at C¯pt≤-0.02marked in Fig. 3 .

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Figure 6

Space-time plot of the relative exit angle for three different positions along the span

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Figure 7

Average variations of the relative Mach number (top) and relative exit angle (bottom) within two cycles of the two periodic phenomena

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Figure 8

Demonstration of rotor-stator interaction patterns, adapted from [10].

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Figure 1

Sectional drawing of the test facility, general arrangement

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Figure 2

Sectional drawing of the test turbine, general arrangement; results described in the paper refer to plane 2

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