Research Papers

Transport of Entropy Waves Within a High Pressure Turbine Stage

[+] Author and Article Information
Paolo Gaetani

Politecnico di Milano,
Dipartimento di Energia,
Laboratorio di Fluidodinamica delle Macchine
Via Lambruschini, 4,
Milano 20158, Italy
e-mail: paolo.gaetani@polimi.it

Giacomo Persico

Politecnico di Milano,
Dipartimento di Energia,
Laboratorio di Fluidodinamica delle Macchine
Via Lambruschini, 4,
Milano 20158, Italy
e-mail: giacomo.persico@polimi.it

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 19, 2018; final manuscript received November 29, 2018; published online January 16, 2019. Editor: Kenneth Hall.

J. Turbomach 141(3), 031006 (Jan 16, 2019) (9 pages) Paper No: TURBO-18-1254; doi: 10.1115/1.4042165 History: Received September 19, 2018; Revised November 29, 2018

This paper presents the results of an experimental study on the transport of entropy waves within a research turbine stage, representative of the key aero-thermal phenomenon featuring the combustor-turbine interaction in aero-engines. The entropy waves are injected upstream of the turbine by a dedicated entropy wave generator (EWG) and are released in axial direction; they feature circular shape with peak amplitude in the center and exhibit sinusoidal-like temporal evolution over the whole wave area. The maximum over-temperature amounts to 7% of the undisturbed flow, while the frequency is 30 Hz. The entropy waves are released in four azimuthal positions upstream of the stage, so to simulate four different burner-to-stator blade clocking. Time-resolved temperature measurements were performed with fast microthermocouples (FTC); the flow and the pressure field upstream and downstream of the stator and the rotor was measured with five-hole pneumatic probes and fast-response aerodynamic pressure probes. The entropy waves are observed to undergo a relevant attenuation throughout their transport within the stator blade row, but they remain clearly visible at the stator exit and retain their dynamic characteristics. In particular, the total temperature distribution appears severely altered by burner-stator clocking position. At the stage exit, the entropy waves loose their coherence, appearing spread in the azimuthal direction to almost cover the entire pitch in the outer part of the channel, while being more localized below midspan. Despite the severe and unsteady interaction of the entropy waves within the rotor, they retain their original dynamic character. A comparison with measurements performed by injecting steady hot streaks is finally reported, remarking both differences and affinities. As a relevant conclusion, it is experimentally shown that entropy waves can be proficiently simulated by considering a succession of hot streaks of different amplitude.

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Grahic Jump Location
Fig. 1

Meridional cut of the test section; T0, T1, T2 = stage-inlet, stator-exit, stage-exit traverses; EWG: entropy wave generator

Grahic Jump Location
Fig. 4

Amplitude of EW temperature oscillations at the stator-exit for the four different injector-stator clocking positions, made nondimensional with respect to the maximum of the entropy wave at the stator inlet reported in Fig. 2 (in Celsius)

Grahic Jump Location
Fig. 2

Amplitude of temperature oscillations in the entropy wave at the stage inlet (T0). Injector aligned with the stator leading edge.

Grahic Jump Location
Fig. 3

Flow field downstream of the stator (T1): (a) total pressure loss, (b) streamwise vorticity, (c) absolute flow angle, and (d) Mach number

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Fig. 10

Time-evolution of the entropy wave at the rotor-exit for stator midpitch injection

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Fig. 5

Entropy wave time evolution for the PS case

Grahic Jump Location
Fig. 8

Temperature fluctuations at the rotor exit made nondimensional with respect to the inlet maximum temperature fluctuation (represented in Fig. 2), for the four EW injection positions

Grahic Jump Location
Fig. 6

Time-averaged flow field in the relative frame downstream of the rotor

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Fig. 7

Total temperature field downstream of the rotor. Stage inlet total temperature = 50 °C.

Grahic Jump Location
Fig. 9

Temperature difference with respect to the case without injection at the rotor exit, for hot streak injection (taken from Ref. [10])



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