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Research Papers

An Experimental Investigation of Adiabatic Film Cooling Effectiveness and Heat Transfer Coefficient on a Transonic Squealer Tip

[+] Author and Article Information
Andrew J. Saul

Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: andrew.saul@eng.ox.ac.uk

Peter T. Ireland

Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: peter.ireland@eng.ox.ac.uk

John D. Coull

Whittle Laboratory,
University of Cambridge,
Cambridge CB3 0DY, UK
e-mail: jdc38@cam.ac.uk

Tsun Holt Wong

Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: holt.wong@eng.ox.ac.uk

Haidong Li

Rolls-Royce PLC,
Bristol BS34 7QE, UK
e-mail: haidong.li@rolls-royce.com

Eduardo Romero

Rolls-Royce PLC,
Bristol BS34 7QE, UK
e-mail: eduardo.romero@rolls-royce.com

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received October 30, 2018; final manuscript received March 20, 2019; published online May 30, 2019. Assoc. Editor: Kenneth Hall.

J. Turbomach 141(9), 091005 (May 30, 2019) (10 pages) Paper No: TURBO-18-1310; doi: 10.1115/1.4043263 History: Received October 30, 2018; Accepted March 20, 2019

The effect of film cooling on a transonic squealer tip has been examined in a high speed linear cascade, which operates at engine-realistic Mach and Reynolds numbers. Tests have been performed on two uncooled tip geometries with differing pressure side rim edge radii, and a cooled tip matching one of the uncooled cases. The pressure sensitive paint technique has been used to measure adiabatic film cooling effectiveness on the blade tip at a range of tip gaps and coolant mass flow rates. Complementary tip heat transfer coefficients have been measured using transient infrared thermography, and the effects of the coolant film on the tip heat transfer and engine heat flux were examined. The uncooled data show that the tip heat transfer coefficient distribution is governed by the nature of flow reattachments and impingements. The squealer tip can be broken down into three regions, each exhibiting a distinct response to a change in the tip gap, depending on the local behavior of the overtip leakage flow. Complementary computational fluid dynamics (CFD) shows that the addition of casing motion causes no change in the flow over the pressure side rim. Injected coolant interacts with the overtip leakage flow, which can locally enhance the tip heat transfer coefficient. The film effectiveness is dependent on both the coolant mass flow rate and tip clearance. At increased coolant mass flow, areas of high film effectiveness on the pressure side rim coincide strongly with a net heat flux reduction and in the subsonic tip region with low heat transfer coefficient.

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Figures

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Fig. 1

CAD of the HSLC test section

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Fig. 2

Squealer tip geometry tested: (a) uncooled tip geometry and (b) cooled tip geometry

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Fig. 3

Regression plot of heat flux versus tip surface temperature for a single location during the transient period

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Fig. 4

Experimental uncooled tip HTC—as-printed Mark I geometry with slight PS rim edge rounding: (a) 0.65% tip gap and (b) 1.15% tip gap

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Fig. 5

Experimental uncooled tip HTC—machined Mark II geometry with sharp PS rim edge (cooled geometry with cooling holes blocked): (a) 0.65% tip gap and (b) 1.15% tip gap

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Fig. 6

CFD uncooled tip HTC: (a) 0.65% tip gap and (b) 1.15% tip gap

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Fig. 7

CFD predictions of Mach for the uncooled squealer tip at 0.65% and 1.15% g/S: (a) and (d) at mid tip gap plane, outline denotes M = 1 and straight lines (labelled 1, 2 and 3) denote the cut-plane locations; (b), (c), (e), and (f) at three cut planes perpendicular to the tip surface, with flow streamlines indicated. (a) 0.65% g/S at mid tip gap. (b) 0.65% g/S at PS rim. (c) 0.65% g/S at SS rim. (d) 1.15% g/S at mid tip gap. (e) 1.15% g/S at PS rim. (f) 1.15% g/S at SS rim.

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Fig. 8

Tip flow mechanisms for a sharp and rounded pressure side rim edge at different tip gaps (high HTC region at reattachment): (a) sharp edge at small tip gap—early reattachment, (b) sharp edge at large tip gap—later reattachment, (c) rounded edge at small tip gap—attached flow, and (d) rounded edge at large tip gap—separated flow

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Fig. 9

CFD uncooled tip HTC with casing motion: (a) 0.65% tip gap and (b) 1.15% tip gap

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Fig. 10

Experimental cooled tip HTC (left) and η (right) contours at 0.65% tip gap and two coolant mass flow rates: (a) HTC, nominal cool; (b) η, nominal cool; (c) HTC, 150% of nominal cool; and (d) η, 150% of nominal cool

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Fig. 11

Experimental cooled tip HTC (left) and η (right) contours at 1.15% tip gap and two coolant mass flow rates: (a) HTC, nominal cool; (b) η, nominal cool; (c) HTC, 150% of nominal cool; and (d) η, 150% of nominal cool

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Fig. 12

NHFR for the 0.65% g/S tip gap: (a) nominal cool and (b) 150% nominal cool

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