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Research Papers

Experimental and Computational Study of the Effect of Momentum-Flux Ratio on High-Pressure Nozzle Guide Vane Endwall Cooling Systems

[+] Author and Article Information
Francesco Ornano

Department Engineering Science,
University of Oxford,
Parks Road,
Oxford OX1 3PJ, UK
e-mail: francesco.ornano@eng.ox.ac.uk

Thomas Povey

Department Engineering Science,
University of Oxford,
Parks Road,
Oxford OX1 3PJ, UK

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 2, 2017; final manuscript received August 15, 2017; published online September 26, 2017. Editor: Kenneth Hall.

J. Turbomach 139(12), 121002 (Sep 26, 2017) (14 pages) Paper No: TURBO-17-1100; doi: 10.1115/1.4037756 History: Received August 02, 2017; Revised August 15, 2017

High-pressure (HP) nozzle guide vane (NGV) endwalls are often characterized by highly three-dimensional (3D) flows. The flow structure depends on the incoming boundary layer state (inlet total pressure profile) and the (static) pressure gradients within the vane passage. In many engine applications, this can lead to strong secondary flows. The prediction and design of optimized endwall film cooling systems is therefore challenging and is a topic of current research interest. A detailed experimental investigation of the film effectiveness distribution on an engine-realistic endwall geometry is presented in this paper. The film cooling system was a fairly conventional axisymmetric double-row configuration. The study was performed on a large-scale, low-speed wind tunnel using infrared (IR) thermography. Adiabatic film effectiveness distributions were measured using IR cameras, and tests were performed across a wide range of coolant-to-mainstream momentum-flux and mass flow ratios (MFRs). Complex interactions between coolant film and vane secondary flows are presented and discussed. A particular feature of interest is the suppression of secondary flows (and associated improved adiabatic film effectiveness) beyond a critical momentum flux ratio. Jet liftoff effects are also observed and discussed in the context of sensitivity to local momentum flux ratio. Full coverage experimental results are also compared to 3D, steady-state computational fluid dynamics (CFD) simulations. This paper provides insights into the effects of momentum flux ratio in establishing similarity between cascade conditions and engine conditions and gives design guidelines for engine designers in relation to minimum endwall cooling momentum flux requirements to suppress endwall secondary flows.

Copyright © 2017 by ASME
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Figures

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Fig. 1

Computer-aided design model and components of the super-scale platform cooling facility: (a) front view and (b) rear view. A—vane and platforms, B—rear cameras, C—front cameras, D—combustor simulator, E—tailboards, F—hub cassette, and G—casing cassette.

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Fig. 2

(a) NGV cascade viewed from upstream, (b) detail of the casing endwall, (c) casing film cooling pattern, and (d) vane hub and casing cooling hole inclinations angles

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Fig. 3

CFD-predicted single vane capacity at six pressure ratios fitted with isentropic trend

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Fig. 4

Fields of view: (a) upstream endwall and (b) downstream endwall

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Fig. 5

Typical calibration curve of detector signal as a function of the surface temperature (thermocouple)

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Fig. 6

Contours of the absolute uncertainty (to 95% confidence) in η as a function of T∞/Tc and η

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Fig. 7

Range of momentum flux ratio for endwall cooling systems at typical engine conditions

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Fig. 8

(a) Surface mesh detail, (b) film cooling hole mesh detail, and (c) computational domain

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Fig. 9

Measured normalized radial total pressure profile at the combustor–NGV interface

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Fig. 10

Film effectiveness distribution along the vane exit line obtained during the grid independency study. The flow conditions were MFR = 3.3% and I = 3.89.

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Fig. 11

Endwall adiabatic film effectiveness contours (upstream view) for 0.40 < I < 6.40

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Fig. 12

Endwall adiabatic film effectiveness contours (upstream view) for 11.65 < I < 26.99

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Fig. 13

Endwall adiabatic film effectiveness contours (downstream view) for 0.40 < I < 26.99

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Fig. 14

Measured tangential distribution of adiabatic film effectiveness downstream the first cooling row (line 1)

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Fig. 15

Measured tangential distribution of adiabatic film effectiveness downstream the second cooling row (line 2)

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Fig. 16

Measured tangential distribution of adiabatic film effectiveness on vane midpassage (line 3)

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Fig. 17

Measured tangential distribution of adiabatic film effectiveness on vane outlet line (line 4)

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Fig. 18

Comparison of adiabatic film effectiveness between CFD and experiment for I = 6.40 (MFR = 4.3%): (a) experimental results, (b) CFD prediction, and (c) comparison at vane inlet and outlet lines with indication of experimental uncertainty, uη

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Fig. 19

Comparison of adiabatic film effectiveness between CFD and experiment for I = 11.65 (MFR = 6.3%): (a) experimental results, (b) CFD prediction, and (c) comparison at vane inlet and outlet lines with indication of experimental uncertainty, uη

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Fig. 20

Laterally averaged adiabatic film effectiveness on lines 1–4 as a function of the momentum flux ratio: experiment (solid markers) and CFD (open markers)

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Fig. 21

(a) Normalized total pressure radial profile, (p0−p0*)/(p0,in−p2ave), for different momentum flux ratios and (b) axial and pitchwise location of the radial traverse

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Fig. 22

Normalized total pressure contours at vane inlet and coolant streamline traces: case with low I (a) and high I (b)

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Fig. 23

PS view of Lambda 2-criterion for (a) I = 0.40 and (b) I = 11.65

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Fig. 24

SS view of Lambda 2-criterion and total pressure loss coefficient, cp0, for (a) I = 0.40 and (b) I = 11.65

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