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Research Papers: Gas Turbines: Turbomachinery

Surface Roughness Impact on Low-Pressure Turbine Performance Due to Operational Deterioration

[+] Author and Article Information
Andreas Kellersmann

Institute of Jet Propulsion and Turbomachinery,
Technische Universität Braunschweig,
Hermann-Blenk-Straße 37,
Braunschweig 38108, Germany
e-mail: a.kellersmann@ifas.tu-braunschweig.de

Sarah Weiler

Institute of Jet Propulsion and Turbomachinery,
Technische Universität Braunschweig,
Hermann-Blenk-Straße 37,
Braunschweig 38108, Germany
e-mail: sarah.weiler@airbus.com

Christoph Bode

Institute of Jet Propulsion and Turbomachinery,
Technische Universität Braunschweig,
Hermann-Blenk-Straße 37,
Braunschweig 38108, Germany
e-mail: chr.bode@ifas.tu-braunschweig.de

Jens Friedrichs

Institute of Jet Propulsion and Turbomachinery,
Technische Universität Braunschweig,
Hermann-Blenk-Straße 37,
Braunschweig 38108, Germany
e-mail: j.friedrichs@ifas.tu-braunschweig.de

Jörn Städing

MTU Maintenance Hannover GmbH,
Münchner Straße 31,
Langenhagen 30855, Germany,
e-mail: joern.staeding@mtu.de

Günter Ramm

MTU Aero Engines AG,
Dachauer Straße 665,
München 80995, Germany
e-mail: guenter.ramm@mtu.de

1Corresponding author.

2Present address: TABG—Programme Performance Management, Airbus Defence and Space, Avenida de Aragón, Madrid 404-28022, Spain.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 6, 2017; final manuscript received August 22, 2017; published online January 17, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(6), 062601 (Jan 17, 2018) (7 pages) Paper No: GTP-17-1308; doi: 10.1115/1.4038246 History: Received July 06, 2017; Revised August 22, 2017

The overall efficiency and operational behavior of aircraft engines are influenced by the surface finish of the airfoils. During operation, the surface roughness significantly increases due to erosion and deposition processes. The aim of this study is to analyze the influence of roughness on the aerodynamics of the low-pressure turbine (LPT) of a midsized high bypass turbofan. In order to gain a better insight into the operational roughness structures, a sample of new, used, cleaned, and reworked turbine blades and vanes are measured using the confocal laser scanning microscopy technique. The measurement results show local inhomogeneities. The roughness distributions measured are then converted into their equivalent sand grain roughness ks,eq to permit an evaluation of the impact on aerodynamic losses. The numerical study is performed using the computational fluid dynamics (CFD)-solver turbomachinery research aerodynamics computational environment (TRACE) which was validated before with the existing data from rig experiments. It is observed that the influence of the surface roughness on the turbine efficiency is significant at take-off but negligible at cruise. A detailed analysis on the aerodynamics at take-off shows that very rough airfoils lead to higher profile and secondary loss. Due to the higher disturbances present in flows circulating over rough walls, the transition occurs earlier, and the momentum thickness increases in the turbulent boundary layer. The service-induced roughness structures cause an efficiency drop in the LPT of ηT=0.16% compared to new parts. A gas path analysis showed that this results in an increased fuel flow of Δm˙f=+0.06% and an exhaust gas temperature (EGT) rise of ΔEGT=+1.2K for fixed engine pressure ratio which is equivalent to roughly 4% of the typical EGT margin of a fully refurbished engine. This result stresses the importance of roughness-induced loss in LPTs.

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Figures

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Fig. 1

Schematic view of measurement positions on the blades

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Fig. 2

Comparison of experimental and numerical turbine efficiency for take-off and cruise conditions

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Fig. 3

Prescription of mean equivalent sand grain roughness for each stage (this study)

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Fig. 4

Overall performance of different prescribed roughnesses

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Fig. 5

Total pressure loss coefficient for the first and second stage

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Fig. 6

Eddy viscosity ratio after second stage

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Fig. 7

Skin friction coefficient at center line of vane and blade of stages 1 and 2

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