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Research Papers: Gas Turbines: Turbomachinery

Accounting for Unsteady Interaction in Transonic Stages

[+] Author and Article Information
Filippo Rubechini

Department of Industrial Engineering,
University of Florence,
via di Santa Marta, 3,
Firenze 50139, Italy
e-mail: filippo.rubechini@arnone.de.unifi.it

Michele Marconcini, Matteo Giovannini, Juri Bellucci, Andrea Arnone

Department of Industrial Engineering,
University of Florence,
via di Santa Marta, 3,
Firenze 50139, Italy

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 24, 2014; final manuscript received August 5, 2014; published online November 25, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(5), 052602 (May 01, 2015) (9 pages) Paper No: GTP-14-1433; doi: 10.1115/1.4028667 History: Received July 24, 2014; Revised August 05, 2014; Online November 25, 2014

This paper discusses the importance of the unsteady interaction in transonic turbomachinery stages. Although the flow in a turbomachine is inherently unsteady, most current calculations for routine design work exploit the steady state assumption. In fact, unsteady flow effects are often taken into account for mechanical integrity checks, such as blade flutter or forced response, or heat transfer issues associated with circumferential nonuniformities, whereas steady state calculations are usually selected for the aerodynamic design. In this work, some cases are discussed in which significant departures are found between steady and time-averaged results, and the basic fluid mechanisms responsible for them are examined. Finally, a current perspective of unsteady computational fluid dynamics (CFD) calculations for the aerodynamic design is given.

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References

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Figures

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Fig. 1

Instantaneous density gradient for different expansion ratios: (a) M2,is = 1.0; (b) M2,is=1.1; and (c) M2,is = 1.3

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Fig. 2

Stage operating conditions at varying the expansion ratio

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Fig. 3

Nozzle profile losses versus nozzle discharge Mach

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Fig. 4

Impact of computational model on performance at varying expansion ratio

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Fig. 5

Averaged entropy rise across the stage for different expansion ratios. Steady and unsteady results.

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Fig. 6

Nozzle Mach number—steady and time-averaged results: (a) M2,is = 1.0; (b) M2,is = 1.1; and (c) M2,is = 1.3

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Fig. 7

Pitchwise pressure nonuniformity at the vane discharge: steady and unsteady results

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Fig. 8

Instantaneous static pressure contours: (a) near stall; (b) peak efficiency; and (c) choke

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Fig. 9

Rotor and overall efficiency versus mass flow

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Fig. 10

Overall performance at full and part load

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Fig. 11

Pitchwise relative Mach number at rotor inlet, at full and part load. Time-averaged results.

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Fig. 12

Instantaneous pressure contours at midspan [11]

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Fig. 13

Load distribution on the nozzle (a) and on the blade (b) at midspan, and spanwise distribution of exit swirl angle (c). Comparison between steady and time-averaged results [11].

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Fig. 14

Measured and computed stage performance

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Fig. 15

Impact of computational model on performance at varying nozzle opening [12]

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