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Research Papers

Off-Design Performance of a Highly Loaded Low Pressure Turbine Cascade Under Steady and Unsteady Incoming Flow Conditions

[+] Author and Article Information
Daniele Simoni

DIME—Università di Genova,
Via Montallegro 1,
Genova I-16145, Italy
e-mail: daniele.simoni@unige.it

Marco Berrino

DIME—Università di Genova,
Via Montallegro 1,
Genova I-16145, Italy
e-mail: marco.berrino@unige.it

Marina Ubaldi

DIME—Università di Genova,
Via Montallegro 1,
Genova I-16145, Italy
e-mail: marina.ubaldi@unige.it

Pietro Zunino

DIME—Università di Genova,
Via Montallegro 1,
Genova I-16145, Italy
e-mail: pietro.zunino@unige.it

Francesco Bertini

AvioAero R&D,
V. I Maggio,
Rivalta (TO) 99 I-10040, Italy
e-mail: francesco.bertini@avioaero.com

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 27, 2014; final manuscript received November 4, 2014; published online January 7, 2015. Editor: Ronald S. Bunker.

J. Turbomach 137(7), 071009 (Jul 01, 2015) (9 pages) Paper No: TURBO-14-1280; doi: 10.1115/1.4029200 History: Received October 27, 2014; Revised November 04, 2014; Online January 07, 2015

The off-design performance of a highly loaded low pressure (LP) turbine cascade has been experimentally investigated, at the Aerodynamics and Turbomachinery Laboratory of Genova University, under steady and unsteady incoming flow conditions. Tests have been performed for different Reynolds numbers (Re = 70,000 and Re = 300,000), in order to cover the typical LP turbine working range. The incidence angle has been varied between i = −9 deg and +9 deg, in order to test off-design conditions characterizing the engine. For the unsteady case, upstream wake periodic perturbations have been generated by means of a tangential wheel of radial rods. The cascade and the moving bars system have been located over a common bearing in order to make them rigidly rotating. This solution allows a proper comparison of the cascade robustness at the incidence angle variation under steady and unsteady incoming flows, since all the other operating parameters have been kept the same. In order to survey the variation of the unsteady boundary conditions characterizing the off-design operation of the downstream cascade, time-mean and time-resolved wake structures have been analyzed in detail. For what concerns the cascade performance, profile aerodynamic loadings and total pressure loss coefficients at the cascade exit have been surveyed for the different incidence angles under both steady and unsteady inflows. Different total pressure loss sensitivity at the incidence angle variation has been observed for the steady and the unsteady inflow conditions. Hot-wire anemometer has been employed to obtain the time-mean pressure and suction side boundary layer velocity profiles at the blade trailing edge for the different conditions. The integral parameters at the cascade exit plane help to justify the different loss trend versus incidence angle found for the steady and the unsteady cases, explaining the different sensibility of the blade profile when this operates under realistic unsteady inflow condition.

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Figures

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Fig. 2

Wake velocity and turbulence profiles at nominal incidence i = 0 deg

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Fig. 3

Comparison of wake velocity and turbulence profiles at different incidences

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Fig. 4

Aerodynamic loading distributions: comparison between steady and unsteady cases

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Fig. 5

Aerodynamic loading distributions: steady case, Re = 70,000

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Fig. 6

Aerodynamic loading distributions: unsteady case, Re = 70,000

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Fig. 7

Suction side velocity profiles at the blade trailing edge, Re = 70,000

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Fig. 8

Boundary layer integral parameters: steady inflow, Re = 70,000

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Fig. 9

Boundary layer integral parameters: unsteady inflow, Re = 70,000

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Fig. 10

Dimensionless total pressure loss coefficient distributions

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Fig. 11

Control volume for the moving bars system

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Fig. 12

Angle variation (top) and total pressure drop (bottom) across the moving bars system

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