Research Papers

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

[+] Author and Article Information
G. Persico

A. Mora, P. Gaetani

Laboratorio di Fluidodinamica delle Macchine, Dipartimento di Energia, Politecnico di Milano, Via Lambruschini 4, I-20158, Milano, Italy

M. Savini

Dipartimento di Ingegneria Industriale,  Università degli Studi di Bergamo, Viale Marconi 5, I-24044 Dalmine, Italy

J. Turbomach 134(6), 061030 (Sep 12, 2012) (10 pages) doi:10.1115/1.4004021 History: Received April 01, 2011; Accepted April 16, 2011; Published September 12, 2012; Online September 12, 2012

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage are studied. In particular, the results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX, are critically evaluated against experimental data. Measurements were carried out with a novel three-dimensional fast-response pressure probe in the closed-loop test rig of the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano. An analysis is first reported about the strategy to limit the CPU and memory requirements while performing three-dimensional simulations of blade row interaction when the rotor and stator blade numbers are prime to each other. What emerges as the best choice is to simulate the unsteady behavior of the rotor alone by applying the stator outlet flow field as a rotating inlet boundary condition (scaled on the rotor blade pitch). Thanks to the reliability of the numerical model, a detailed analysis of the physical mechanisms acting inside the rotor channel is performed. Two operating conditions at different vane incidence are considered, in a configuration where the effects of the vortex-blade interaction are highlighted. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator, thus promoting different interaction processes in the subsequent rotor channel. However some general trends can be recognized in the vortex-blade interaction: the sense of rotation and the spanwise position of the incoming vortices play a crucial role on the dynamics of the rotor vortices, determining both the time-mean and the time-resolved characteristics of the secondary field at the exit of the stage.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Rotor channel grid

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Figure 2

Spanwise profile of total pressure and flow angles for I-0

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Figure 3

Time-mean flow in the rotating frame—I-0; experimental (top) and numerical (bottom) comparison; from left to right: relative total pressure coefficient, deviation angle, radial flow angle, and blade to blade flow angle

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Figure 4

Entropy and vorticity field at the rotor inlet for I-0 (top) and I-20 (bottom)

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Figure 5

Evolution of the entropy and vorticity field inside the rotor channel, I-0 configuration(suction side on the left of the blade)

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Figure 6

Snapshots of relative streamwise vorticity at 85% span for I-0 at τ = 0.4, 0.6, 1.2

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Figure 7

Entropy field, relative streamwise vorticity, and numerical and experimental deviation angle at the rotor exit I-0. (a) Phase of rotor-dominated flow field and (b) phase of maximum interaction effects.

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Figure 8

Evolution of the entropy and vorticity field inside the rotor channel, I-20 configuration(suction side on the left of the blade)

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Figure 9

Streamwise vorticity and deviation angle at the rotor exit in two instants, I-20. (a) Phase of rotor dominated flow field and (b) phase of max. vane-rotor interaction effects.

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Figure 10

Radial profiles of absolute flow angle, total temperature drop, deviation angle, and entropy generation at the rotor exit



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