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Research Papers

Analysis of the Unsteady Overtip Casing Heat Transfer in a High Speed Turbine

[+] Author and Article Information
S. Lavagnoli

e-mail: lavagnoli@vki.ac.be

G. Paniagua

e-mail: paniagua@vki.ac.be

C. De Maesschalck

e-mail: demaess@vki.ac.be

T. Yasa

e-mail: yasa@vki.ac.be
von Karman Institute for Fluid Dynamics,
Rhode-Saint-Genèse, Belgium

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 4, 2012; final manuscript received August 8, 2012; published online March 25, 2013. Editor: David Wisler.

J. Turbomach 135(3), 031027 (Mar 25, 2013) (12 pages) Paper No: TURBO-12-1126; doi: 10.1115/1.4007509 History: Received July 04, 2012; Revised August 08, 2012

In modern gas turbine engines, the rotor casing is vulnerable to thermal failures due to large unsteady heat fluxes. The rotor tip flow unsteadiness is induced by the periodic passage of the rotor blades, with an intensity dependent on the tip gap geometry. Hence, the understanding of the physics is of paramount importance to develop appropriate predictive tools and improve the cooling schemes. The present research aims at providing essential information on the flow conditions, which should serve to assess the relative impact of the overtip flow, tip gap magnitude, and work extraction processes on the casing thermal load. This paper presents simultaneous measurements of steady and unsteady heat transfer, pressure and rotor tip clearance in the casing of a transonic turbine stage. The research article was tested in a compression tube facility operating at engine representative conditions (vane Mach number 1.07, vane outlet Reynolds number 1.3 × 106, pressure ratio is 2.92, at 6790 rpm). The rotor blade geometry has a flat tip with a nominal tip clearance of about 0.4% of blade height. The heat transfer, pressure, and tip clearance data were obtained at three circumferential positions around the turbine casing. The heat flux was monitored using a single-layered thin film gauge able to resolve with high fidelity the wall temperature fluctuations. The heat flux sensor was mounted on a probe equipped with a heating device that allows varying the wall temperature. A series of experiments was performed at different heating rates to derive the local adiabatic wall temperature and the adiabatic convective heat transfer coefficient. A high bandwidth capacitive sensor provided the instantaneous value of the single blade tip clearance. A simple zero-dimensional model has been proved effective to predict the local flow temperature while the rotor spins up prior to the test, and estimate the overtip flow temperature during a test.

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Figures

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Fig. 1

3D view of the turbine stage (left), rotor blade with flat tip (right)

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Fig. 2

Compression tube facility overview (left), change of conditions in a typical test (right)

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Fig. 3

Experimental and predicted tip clearance envelope during turbine test rig operation

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Fig. 4

Blade-to-blade radius variation from the longest blade in static and running conditions

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Fig. 5

Installation of the casing instrumentation on the turbine rig (a) circumferential locations of the instrumented probe (b) meridional view of the turbine test section (c) axial location of the probe

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Fig. 6

Heat transfer probe design and instrumented ceramic insert

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Fig. 7

(a) Cut view of the fast-response pressure probe (b) tip clearance measurement system and its installation on the rotor casing

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Fig. 8

Procedure for heat transfer and adiabatic wall temperature data reduction

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Fig. 9

Measured casing wall time-resolved adiabatic wall temperature, Nusselt number, and static pressure as a function of rotor phase

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Fig. 10

Adiabatic wall temperature, Nusselt number, and static pressure correlation with the blade-to-blade tip clearance

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Fig. 11

Blade-to-blade signature of adiabatic wall temperature, Nusselt number, static pressure, and tip clearance for a blow-down experiment (left) and for a run-up (right)

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Fig. 12

Adiabatic wall temperature correlation with the rotor speed

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Fig. 13

Model of the flow work process on the rotor tip for a run-up test and a blow-down

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Fig. 14

Predicted leakage flow absolute total temperature variations for a range of Mach numbers and flow angles, temperature variations sensitivity to change in tip leakage flow angle at different Mach numbers

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