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Research Papers

Effects of Trenched Holes on Film Cooling of a Contoured Endwall Nozzle Vane

[+] Author and Article Information
Giovanna Barigozzi

Dipartimento di Ingegneria Industriale, Università degli Studi di Bergamo, Viale Marconi, 24044 Dalmine (BG), Italygiovanna.barigozzi@unibg.it

Giuseppe Franchini

Dipartimento di Ingegneria Industriale, Università degli Studi di Bergamo, Viale Marconi, 24044 Dalmine (BG), Italygiuseppe.franchini@unibg.it

Antonio Perdichizzi

Dipartimento di Ingegneria Industriale, Università degli Studi di Bergamo, Viale Marconi, 24044 Dalmine (BG), Italyantonio.perdichizzi@unibg.it

Silvia Ravelli

Dipartimento di Ingegneria Industriale, Università degli Studi di Bergamo, Viale Marconi, 24044 Dalmine (BG), Italysilvia.ravelli@unibg.it

J. Turbomach 134(4), 041009 (Jul 20, 2011) (10 pages) doi:10.1115/1.4003658 History: Received September 20, 2010; Revised October 17, 2010; Published July 20, 2011; Online July 20, 2011

The present paper investigates the effects of the application of trenched holes in the front part of a contoured film cooled endwall. Two trench configurations were tested, changing the trench depth. Tests have been carried out at low speed (M2is=0.2) and low inlet turbulence intensity level, with coolant mass flow rate ratio varied within the 0.5–2.5% range. Pressure probe traverses were performed downstream of the vane trailing edge to show the secondary flow field modifications and to evaluate trench additional losses. Endwall distributions of film cooling effectiveness have been obtained by the thermochromic liquid crystal (TLC) technique. For each injection condition, energy loss coefficient and film cooling effectiveness distributions were analyzed and compared with the ones obtained from rows of cylindrical holes. Laterally and area averaged effectiveness as well as pitch and mass averaged kinetic energy loss coefficients were computed to enlighten any change induced by the introduction of trenched holes. A uniform and high thermal coverage was obtained in the region just downstream of the trench, but it quickly decayed because of enforced mixing of coolant with main flow. Compared with the cylindrical hole configuration, trenches are able to provide a higher global cooling effectiveness, but a larger amount of coolant injection is required. The introduction of both trenches is responsible for a secondary thermodynamic loss increase of about 0.7% at low coolant injection rates. Increasing the blowing rates, the additional loss vanishes.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

The wind tunnel (1: inlet duct; 2: test section; 3: tailboard; 4: diffuser; 5: fan; 6: ac motor; 7: discharge channel)

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Figure 2

Meridional profile

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Figure 3

Cascade and endwall cooling geometry

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Figure 4

Detail of trenched hole geometries

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Figure 5

Row A and B local blowing ratios—cylindrical case (4)

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Figure 7

TLC calibration curves

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Figure 8

Cascade local ζ distributions without cooling (a) solid and (b) trenched endwalls (t=1.0D)

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Figure 9

Spanwise (a) flow angle deviation and (b) primary loss distributions—no coolant flow

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Figure 10

Local ζ distributions for different MFRs: (a) 0.4% (M1=0.71), (b) 1.0% (M1=2.1), (c) 1.6% (3.3), and (d) 2.5% (M1=5.2)

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Figure 11

Spanwise (a) flow angle deviation and (b) primary loss distributions for variable injection conditions

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Figure 12

Cylindrical cooling scheme cascade local ζ distributions at (a) MFR=0.52%(M1=0.73) and (b) MFR=2.3%(M1=5)

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Figure 13

Mass averaged primary and thermodynamic secondary energy loss coefficients versus M1

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Figure 14

Coolant mass flow injected through trenches versus M1

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Figure 15

Local momentum flux ratios for selected injection conditions—cylindrical holes

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Figure 16

Film cooling effectiveness distributions for the different injection conditions—cylindrical

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Figure 17

Film cooling effectiveness distributions for the different injection conditions and the two trench depths

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Figure 18

Pitch averaged η distributions for variable MFR

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Figure 19

Pitch averaged η distributions at best MFRA+B

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Figure 20

Area averaged η distributions versus MFR

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