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TECHNICAL PAPERS

Investigation of the Flow Field in a High-Pressure Turbine Stage for Two Stator-Rotor Axial Gaps—Part II: Unsteady Flow Field

[+] Author and Article Information
P. Gaetani

Dipartimento di Energetica, Politecnico di Milano, Via la Masa 34, I-20158, Italypaolo.gaetani@polimi.it

G. Persico, V. Dossena, C. Osnaghi

Dipartimento di Energetica, Politecnico di Milano, Via la Masa 34, I-20158, Italy

J. Turbomach 129(3), 580-590 (Jul 23, 2006) (11 pages) doi:10.1115/1.2472393 History: Received July 13, 2006; Revised July 23, 2006

An extensive experimental analysis was carried out at Politecnico di Milano on the subject of unsteady flow in high pressure (HP) turbine stages. In this paper, the unsteady flow measured downstream of a modern HP turbine stage is discussed. Traverses in two planes downstream of the rotor are considered, and, in one of them, the effects of two very different axial gaps are investigated: the maximum axial gap, equal to one stator axial chord, is chosen to “switch off” the rotor inlet unsteadiness, while the nominal gap, equal to 1/3 of the stator axial chord, is representative of actual engines. The experiments were performed by means of a fast-response pressure probe, allowing for two-dimensional phase-resolved flow measurements in a bandwidth of 80kHz. The main properties of the probe and the data processing are described. The core of the paper is the analysis of the unsteady rotor aerodynamics; for this purpose, instantaneous snapshots of the rotor flow in the relative frame are used. The rotor mean flow and its interaction with the stator wakes and vortices are also described. In the outer part of the channel, only the rotor cascade effects can be observed, with a dominant role played by the tip leakage flow and by the rotor tip passage vortex. In the hub region, where the secondary flows downstream of the stator are stronger, the persistence of stator vortices is slightly visible in the maximum stator-rotor axial gap configuration, whereas in the minimum stator-rotor axial gap configuration their interaction with the rotor vortices dominates the flow field. A good agreement with the wakes and vortices transport models has been achieved. A discussion of the interaction process is reported giving particular emphasis to the effects of the different cascade axial gaps. Some final considerations on the effects of the different axial gap over the stage performances are reported.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Measurement scheme (fast-response probe sketched at TR2)

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Figure 2

Mean rotor channel at TR1, maximum stator-rotor gap

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Figure 3

Cpt,R and δ rms at TR1, maximum gap

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Figure 4

Instantaneous rotor flow at TR1, maximum stator-rotor gap (phase-lag periodicity applied)

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Figure 5

Simple kinematic model of the wake/vortex transport in a turbine rotor

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Figure 6

Mean rotor channel at TR2, maximum stator-rotor gap

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Figure 7

Cpt,R and δ rms at TR2, maximum gap

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Figure 8

Mean rotor channel at TR2, nominal stator-rotor gap

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Figure 9

Cpt,R and δ rms at TR2, nominal gap

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Figure 10

Instantaneous rotor flow at TR2, nominal stator-rotor gap (phase-lag periodicity applied)

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Figure 11

Tangential Mach number at TR2: (a) mean rotor channel–maximum gap, (b) mean rotor channel–nominal gap, and (c,d) instantaneous rotor flow–nominal gap

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