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Research Papers

Effect of Tip Clearance Dimensions and Control of Unsteady Flows in a Multi-Stage High-Pressure Compressor

[+] Author and Article Information
Nicolas Gourdain

Fabien Wlassow

CERFACS, Computational Fluid Dynamics Team, 42, avenue Gaspard Coriolis, Toulouse, F-31057, FranceFabien.Wlassow@cerfacs.fr

Xavier Ottavy

Laboratoire de Mécanique des Fluides et d’Acoustique, UMR CNRS 5509, Ecole Centrale Lyon, 36 avenue Guy de Collongue, Ecully, F-69130, FranceXavier.Ottavy@ec-lyon.fr

J. Turbomach 134(5), 051005 (May 08, 2012) (13 pages) doi:10.1115/1.4003815 History: Received October 01, 2009; Revised November 11, 2011; Published May 08, 2012; Online May 08, 2012

This paper describes the investigations performed to better understand unsteady flows that develop in a three-stage high-pressure compressor. More specifically, this study focuses on rotor-stator interactions and tip leakage flow effects on overall performance and aerodynamic stability. The investigation method is based on three-dimensional unsteady RANS simulations, considering the natural spatial periodicity of the compressor. Indeed, all information related to rotor-stator interactions can be computed. A comparison is first done with experimental measurements to outline the capacity of the numerical method to predict overall performance and unsteady flows. The results show that the simulation correctly estimates most flow features in the multistage compressor. Then numerical data obtained for three configurations of the same compressor are analyzed and compared. Configurations 1 and 2 consider two sets of tip clearance dimensions and a casing treatment based on a honeycomb design is applied for configuration 3. Detailed investigations of the flow at the same operating line show that the tip leakage flow is responsible for the loss of stability in the last stage. An increase by 30% of the tip clearance dimension dramatically reduces the stable operating range (by 40% with respect to the standard configuration). A modal analysis shows that the stall process in this case involves the perturbation of the flow in the last rotor by upstream stator wakes, leading to the development of a rotating instability. The control device designed and investigated in this study allows for reducing the sensitivity of the compressor to tip leakage flow by recovering the initial stable operating range.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 7

Instantaneous flow field colored with entropy at near stall operating conditions (full annulus simulation): (a) radial slice at h/H = 83.7%, and (b) axial slice at section 28A

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Figure 8

Fluctuations of axial velocity u′ registered at section 28A (h/H = 83.7%). Comparison of the periodic sector and the full annulus approaches at near stall operating conditions.

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Figure 9

Comparisons of numerical data with measurements for configuration 1: (a) pressure ratio, and (b) isentropic efficiency

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Figure 10

Fluctuation of axial velocity u′ at the design operating point (h/H = 83.7%, section 28A): (a) URANS simulation, and (b) measurements. Each light strip corresponds to the passage of a rotor wake in the absolute frame (5 rotor passages for the periodic sector).

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Figure 11

Overall aerodynamic performance of the three compressor configurations: (a) pressure ratio, and (b) isentropic efficiency

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Figure 12

(a)-(c) Time-averaged solution of axial velocity at h/H = 97% and (d)-(f) spatial Fourier modes at section 28A (at the investigated operating line, as defined in Fig. 1): (a) and (d) configuration 1 (STC), (b) and (e) configuration 2 (LTC), and (c) and (f) configuration 3 (with control)

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Figure 13

Regions of low axial momentum with respect to the axial position in the compressor (see Eq. 5) at the investigated operating line (as defined in Fig. 1)

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Figure 14

Proposition of a scenario to explain the interaction between incoming wakes and the tip leakage jet flow (here, middle blade). Velocity vectors are given in the relative frame of the rotor.

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Figure 15

Radial evolution of the flow variables at the investigated operating line (as defined in Fig. 1): (a) relative flow angle β at section 280 (rotor 3 inlet), (b) absolute flow angle α at section 28A (rotor 3 outlet), and (c) axial velocity u at section 28A (rotor 3 outlet)

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Figure 16

Time-averaged static pressure near the casing of rotor 3 at the investigated operating line, as defined in Fig. 1 (results are spatially averaged on the last 10% of the rotor span)

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Figure 6

Differences between the time-averaged unsteady and the steady flow solutions (configuration 1, axial velocity flow fields): (a) section 26A (first stage), and (b) section 28A (third stage)

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Figure 5

Mass flow evolution at the compressor inlet (configuration 1)

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Figure 4

View of the control device and cavity dimensions applied to the third rotor

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Figure 3

View of the numerical grid at mid-span (1 over 3 points)

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Figure 2

Definition of the tip clearance dimensions

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Figure 1

Axial view of the CREATE compressor and measurement positions

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