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Research Papers

On the Simulation and Spectral Analysis of Unsteady Turbulence and Transition Effects in a Multistage Low Pressure Turbine

[+] Author and Article Information
Georg Geiser

Institute of Propulsion Technology,
German Aerospace Center (DLR),
Linder Höhe,
Cologne 51147, Germany
e-mail: Georg.Geiser@dlr.de

Jens Wellner, Edmund Kügeler, Anton Weber

Institute of Propulsion Technology,
German Aerospace Center (DLR),
Linder Höhe,
Cologne 51147, Germany

Anselm Moors

MTU Aero Engines AG,
Dachauer Straße 665,
Munich 80995, Germany

1Corresponding author.

2Present address: Exa GmbH, Landshuter Allee 8, Munich 80637, Germany.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 5, 2018; final manuscript received October 19, 2018; published online January 25, 2019. Editor: Kenneth Hall.

J. Turbomach 141(5), 051012 (Jan 25, 2019) (9 pages) Paper No: TURBO-18-1281; doi: 10.1115/1.4041820 History: Received October 05, 2018; Revised October 19, 2018

A nonlinear full-wheel time-domain simulation of a two-stage low pressure turbine is presented, analyzed, and compared with the available experimental data. Recent improvements to the computational fluid dynamics (CFD) solver TRACE that lead to significantly reduced wall-clock times for such large scale simulations are described in brief. Since the configuration is characterized by significant unsteady turbulence and transition effects, it is well suited for the validation and benchmarking of frequency-domain methods. Transition, flow separation and wall pressure fluctuations on the stator blades of the second stage are analyzed in detail. A strong azimuthal π-periodicity is observed, manifesting in a significantly varying stability of the midspan trailing edge flow with a quasi-steady closed separation bubble on certain blades and highly dynamic partially open separation bubbles with recurring transition and turbulent reattachment on other blades. The energy spectrum of fluctuating wall quantities in that regime shows a high bandwidth and considerable disharmonic content, which is challenging for frequency-domain-based simulation methods.

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Figures

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Fig. 1

Two-stage ATRD turbine rig. Vane2 midspan channel passage is equipped with Kulite transducers.

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Fig. 2

Speedup of the present full-wheel turbine test case for various TRACE versions versus TRACE 8.2. All benchmarks have been conducted on 40 × 2 × Intel Xeon E5-2695 v2 at 2.40 GHz with hyper-threading enabled.

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Fig. 3

CFD grid topology. Left: blade-to-blade OCGH topology for hub section, right: S3 view showing O- and C-type block near the trailing edge.

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Fig. 4

Grid convergence index GCI for isentropic efficiency and mass flow over the ATRD turbine for three different mesh resolution levels

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Fig. 5

Probability of suction side flow separation at the midspan blade cuts of Vane2. Solid lines indicate attached and fully separated regions, dashed lines indicate intermediate probabilities at 25%, 50%, and 75%. Dash-dotted lines indicate two blades (A and B) of interest for closer investigation.

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Fig. 6

Time evolution of mean boundary layer intermittency Γ (top) and turbulent eddy viscosity ratio μt/μ near the wall (bottom) of the suction sides at midspan of Vane2's blades A (left) and B (right). Solid lines indicate flow separation and reattachment (τw = 0).

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Fig. 7

Top: wall shear stress spectral energy versus Blade1 and Blade1 + Blade2 harmonics at suction side midspan of Vane2's blades A (left) and B (right). Bottom: time-mean and spectral energy of mean boundary layer intermittency versus Blade1 and Blade1 + Blade2 harmonics at suction side midspan of Vane2's blades A (left) and B (right).

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Fig. 8

Normalized first Blade1 harmonic of the midspan wall pressure on the suction (left) and pressure (right) sides of Vane2's blades

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Fig. 9

Normalized first Blade1 harmonic of the midspan wallpressure in a passage of Vane2 located at φle≈−0.125π compared to experimental data

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Fig. 10

Unsteady wall pressure spectral energy budgets at suction side midspan of Vane2's blades A (left) and B (right). Top: total unsteady pressure spectral energy versus Blade1 and Blade1 + Blade2 harmonics, middle: spectral energy share of low-pass filtered Blade1 harmonics (solid lines at odd, dotted lines at even number of modes m considered), bottom: spectral energy share of low-pass filtered Blade2 harmonics (line patterns as above).

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