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Research Papers

Aerodynamic Analysis of an Innovative Low Pressure Vane Placed in an s-Shape Duct

[+] Author and Article Information
Sergio Lavagnoli

 von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, 1640, Belgiumlavagnoli@vki.ac.be

Tolga Yasa

 von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, 1640, Belgiumyasa@vki.ac.be

Guillermo Paniagua

 von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, 1640, Belgiumpaniagua@vki.ac.be

Lionel Castillon

 ONERA, Meudon 92190, Francelionel.castillon@onera.fr

Simone Duni

 von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, 1640, Belgiumduni@vki.ac.be

J. Turbomach 134(1), 011013 (May 27, 2011) (13 pages) doi:10.1115/1.4003241 History: Received September 08, 2010; Revised October 20, 2010; Published May 27, 2011; Online May 27, 2011

In this paper the aerodynamics of an innovative multisplitter low pressure (LP) stator downstream of a high pressure turbine stage is presented. The stator row, located inside a swan necked diffuser, is composed of 16 large structural vanes and 48 small airfoils. The experimental characterization of the steady and unsteady flow fields was carried out in a compression tube rig under engine representative conditions. The one-and-a-half turbine stage was tested at three operating regimes by varying the pressure ratio and the rotational speed. Time-averaged and time-accurate surface pressure measurements are used to investigate the aerodynamic performance of the stator and the complex interaction mechanisms with the high pressure (HP) turbine stage. Results show that the strut blade has a strong impact on the steady and unsteady flow fields of the small vanes depending on the vane circumferential position. The time-mean pressure distributions around the airfoils show that the strut influence is significant only in the leading edge region. At off-design condition (higher rotor speed) a wide separated region is present on the strut pressure side and it affects the flow field of the adjacent vanes. A complex behavior of the unsteady surface pressures was observed. Up to four pressure peaks are identified in the time-periodic signals. The frequency analysis also shows a complex structure. The spectrum distribution depends on the vane position. The contribution of the harmonics is often larger than the fundamental frequency. The forces acting on the LP stator vanes are calculated. The results show that higher forces act on the small vanes but largest fluctuations are experienced by the strut. The load on the whole stator decreases 30% as the turbine pressure ratio is reduced by approximately 35%.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Meridional view of the test section (left), HP turbine and LP vane 3D view, and comparison of strut and aerovane profiles (right)

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Figure 2

Compression tube facility overview (left) and change of conditions in a typical test (right)

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Figure 3

Extractable LP vanes and locations of the pressure sensors

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Figure 4

View of the computational grid

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Figure 5

Steady static pressure distribution on the stator strut (top) and aerovanes (bottom) at three operating conditions: nom-nom (left), low-low (center), and low-nom (right)

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Figure 6

Prediction of flow separation on the strut pressure side at the low-nom condition; instantaneous contour plot of turbulent to laminar viscosity ratio at 50% span (a), isosurface of flow velocity (b), and casing static pressure distribution at two circumferential positions (c)

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Figure 7

Numerical results for absolute flow angle (a) and Mach number (b) variation along the circumferential direction at two axial planes upstream and downstream the strut LE

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Figure 8

Isentropic relative Mach number at the rotor exit at 50% span

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Figure 9

PLA traces at LE of strut and aerovanes B and C at the design condition

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Figure 10

Measured pressure fluctuations on LPV airfoils, 50% span, and design condition

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Figure 11

Periodic pressure envelopes and mean rms along the LPV airfoils for the three turbine regimes

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Figure 12

Amplitude spectrum of surface pressure on LPV airfoils at the three operating conditions

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Figure 13

Tangential and axial forces on the four airfoils

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Figure 14

Variation of the modulus and angle

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Figure 15

Variation of the force on the LP stator row

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