Research Papers: Gas Turbines: Structures and Dynamics

An Experimental Study of the Aerodynamic Forcing Function in a 1.5 Steam Turbine Stage

[+] Author and Article Information
Giacomo Gatti

Laboratorio di Fluidodinamica delle Macchine,
Energy Department—Politecnico di Milano,
Via Lambruschini 4,
Milan 20156, Italy
e-mail: giacomo.gatti@polimi.it

Paolo Gaetani, Berardo Paradiso, Vincenzo Dossena

Laboratorio di Fluidodinamica delle Macchine,
Energy Department—Politecnico di Milano,
Via Lambruschini 4,
Milan 20156, Italy

Juri Bellucci

Department of Industrial Engineering,
University of Florence,
Via S. Marta 3,
Florence 50139, Italy

Lorenzo Arcangeli, Nicola Maceli

GE Oil&Gas,
Via F. Matteucci 2,
Florence 50127, Italy

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 21, 2016; final manuscript received August 29, 2016; published online December 1, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(5), 052503 (Dec 01, 2016) (8 pages) Paper No: GTP-16-1355; doi: 10.1115/1.4034967 History: Received July 21, 2016; Revised August 29, 2016

The usual ways to measure the aerodynamic forcing function are complex and expensive. The aim of this work is to evaluate the forces acting on the blades using a relatively simpler experimental methodology based on a time-resolved pressure measurement at the rotor discharge. Upstream of the rotor, a steady three holes probe (3HP) has been used. The postprocessing procedures are described in detail, including the application of a phase-locked average and of an extension algorithm with phase-lag. The algorithm for the computation of the force components is presented, along with the underlying assumptions. In order to interpret the results, a preliminary description of the flowfield, both upstream and downstream of the rotor, is provided. This gives an insight of the most relevant features that affect the computation of the forces. Finally, the analysis of the results is presented. These are first described and then compared with overall section-average results (torque-sensor), and with the results from 3D unsteady simulations (integral of pressure over the blade surface) in order to assess the accuracy of the method. Both the experimental and the numerical results are also compared for two different operating conditions with increasing stage load.

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Fig. 1

The low-speed closed-loop test rig. Technical scheme and main components: (a) turbine stage, (b) torque-sensor, (c)axial compressor, (d) DC motor, (e) centrifugal blower, (f)venturi nozzle, and (g) heat exchanger.

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Fig. 2

Measurement planes. The steady 3HP is inserted in plane 1, the fast-response FRAPP is inserted in plane 2. The azimuthal distance between the two planes is 30 deg.

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Fig. 3

Conceptual scheme of the extension algorithm (phase-lag)

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Fig. 4

Blade-to-blade view of the computational mesh

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Fig. 5

Steady flowfield downstream of S1: Contours and pitchwise averages on a single stator pitch. On top the tangential velocity, below the static pressure. The dashed lines delimit the channel. Experimental results.

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Fig. 6

Time-resolved flowfield downstream of R, φ=0 : Contours of the tangential velocity and of the static pressure, relative to the maximum values. The dashed lines delimit the channel. Experimental results.

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Fig. 7

Flowfield downstream of R, three stator pitches: Contours of the time-average static pressure field (left) and of the periodic unsteadiness for φ=0 (right). Experimental results.

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Fig. 8

Axial (a) and tangential (b) force over the azimuthal coordinate for two rotor phases. MinL point. Experimental results.

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Fig. 9

Axial (a) and tangential (b) force over the azimuthal coordinate for two rotor phases. MaxL point. Experimental results.

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Fig. 10

Axial (a) and tangential (b) force over the rotor phase. MinL point. CFD results.



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