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Research Papers

Method for Accurately Evaluating Flow Capacity of Individual Film-Cooling Rows of Engine Components

[+] Author and Article Information
Benjamin Kirollos

Osney Thermofluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK
e-mail: ben.kirollos@oxford-flow.com

Thomas Povey

Osney Thermofluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK
e-mail: thomas.povey@eng.ox.ac.uk

1Corresponding author.

Manuscript received November 2, 2016; final manuscript received May 15, 2017; published online July 19, 2017. Assoc. Editor: Ardeshir (Ardy) Riahi.

J. Turbomach 139(11), 111004 (Jul 19, 2017) (17 pages) Paper No: TURBO-16-1287; doi: 10.1115/1.4037028 History: Received November 02, 2016; Revised May 15, 2017

A laboratory experimental method and an analysis technique are presented for evaluation of individual film-cooling row flow capacity characteristics. The method is particularly suited to complex systems such as hot section nozzle guide vanes (NGV) with lossy feed system characteristics. The method is believed to be both more accurate and more experimentally efficient than previous techniques. The new analysis technique uses an experimentally calibrated network model to represent the complex feed system and replaces the need for internal loss measurements, which are both demanding and inaccurate. Experiments are performed in the purpose-built University of Oxford Coolant Capacity Rig (CCR), a bench-top, blow-down type facility with atmospheric back-pressure. The design of the CCR is informed by the requirements to assess engine-scale film-cooled components rapidly, accurately, and precisely. Improvements in the experimental method include a differential mass flow rate measurement method (which eliminates the effect of leaks and minimizes the number of rows that must be blanked, ensuring that the internal coupling is as close as possible to the engine condition) and a variable bypass flow which ensures the mass flow measurement nozzle always operates within its calibrated range. We demonstrate the method using two high-pressure (HP) NGV designs: an engine part with relatively uncoupled (in terms of internal loss) cooling rows; and a laser-sintered part with highly coupled cooling rows. We show that the individual-row flow capacity of a high-pressure nozzle guide vane (HPNGV) can be evaluated in the CCR in a single day to a 2σ precision of approximately 0.5% and a 2σ accuracy (bias) of 0.6%. The importance of performing individual-row capacity measurements is demonstrated: failure to scale flow capacity on a row-by-row basis introduces an error of 30% in the engine situation.

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Figures

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Fig. 1

Photograph of Coolant Capacity Rig

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Fig. 2

Photographs of vanes in Coolant Capacity Rig: (L) cast pair and (R) laser-sintered single

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Fig. 3

Schematic of Coolant Capacity Rig

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Fig. 5

Differential mass flow measurement technique: row capacity measurement Γir(Пa); high-differential system capacity measurement ΓH(Пa); and low-differential system capacity measurement Γi,Lr(Пa) with row of interest blocked

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Fig. 6

Capacity measurement of a single cooling row Γir(Пa) determined from differential measurements using four different bypass flow settings

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Fig. 7

The Oxford University Annular Sector Heat Transfer Facility: (a) radial slice of Sector Facility working section, (b) upstream of vanes; inlet contraction removed, and (c) meridional slice of Sector Facility working section

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Fig. 8

Schematic of geometry A (not to scale) from Ref. [9]

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Fig. 9

Experimentally measured whole vane coolant capacity Γt(Пa), and individual row capacities Γir(Пa) plotted cumulatively (i.e., line S5 + is the sum of the individual capacities). Geometry A, all rows exhausting to atmosphere.

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Fig. 10

Experimentally measured whole vane coolant capacity Γt(Пa) and compartment capacity Γjc(Пa) plotted cumulatively (i.e., line LEC + is the sum of the LEC capacity and the TEC capacity). Geometry A.

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Fig. 11

Experimentally measured compartmental capacity Γjc(Пa) and whole vane coolant capacity Γt(Пa) compared to the sum of individual row capacities Γir(Пa) within each compartment. Geometry A.

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Fig. 12

Effective row areas Air of geometry A as a function of local pressure ratio p0c/pext,ir

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Fig. 13

Cumulative row coolant capacity Γ̃ir(Пe,i) prediction with engine-representative external pressure distribution validated using sector facility experiments at engine-representative conditions (geometry A). Note, individual row capacities are plotted cumulatively so that S5 + is the sum of all rows.

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Fig. 14

Schematic of geometry B (not to scale)

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Fig. 15

Experimentally measured whole vane coolant capacity Γt(Пa) and individual row capacities Γir(Пa) plotted cumulatively (i.e., line S5 + is the sum of the individual capacities). Geometry B, all rows exhausting to atmosphere.

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Fig. 16

Experimentally measured whole vane coolant capacity Γt(Пa) and compartment capacity Γjc(Пa) plotted cumulatively (i.e., line LEC + is the sum of the LEC capacity and the TEC capacity). Geometry B.

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Fig. 17

Experimentally measured compartmental capacity Γjc(Пa) and whole vane coolant capacity Γt(Пa) compared to the sum of individual row capacities Γir(Пa) within each compartment for geometry B

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Fig. 18

Network flow model (geometry B). Circle: compressible flow through film-cooling row; square: incompressible loss element.

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Fig. 19

Effective row areas Air of geometry B as a function of local pressure ratio. For TE-S3, local pressure ratio = p0c/pext,ir; for S5 and S4, local pressure ratio = p0,RPCc/pext,ir.

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Fig. 20

Dimensionless loss coefficient KRPCc of geometry B asa function of pressure ratio across RPC. Nominal flow area ARPCc  = 50 mm2.

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Fig. 21

Network flow model predicted individual row coolant capacity Γ̃ir(Пa)  when all rows exhaust to atmosphere (plotted cumulatively, i.e., S5 + is the sum of all rows), compared to the experimental whole vane coolant capacity Γt(Пa) and experimental individual-row capacity sum ∑Γir(Пa). Geometry B.

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Fig. 22

Individual row coolant capacity (Γ̃ir(Пe,RPC) S5-S4, Γ̃ir(Пe,i) S3-TE) with engine- and sector-representative external pressure distributions (plotted cumulatively, i.e., S5 + is the sum of all rows). Predicted using network flow model and validated using sector facility experiments (sector: γc=γm= 1.4; engine: γc= 1.33, γm= 1.3). Geometry B.

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