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Research Papers

Flow Dynamics of a Film Cooling Jet Issued From a Round Hole Embedded in Contoured Crater

[+] Author and Article Information
Prasad Kalghatgi

Center for Turbine Innovation and Energy Research,
Department of Mechanical Engineering,
Louisiana State University,
Baton Rouge, LA 70803
e-mail: Prasad.Kalghatgi@woodplc.com

Sumanta Acharya

Center for Turbine Innovation and Energy Research,
Department of Mechanical Engineering,
Louisiana State University,
Baton Rouge, LA 70803
e-mail: sacharya1@iit.edu

1Corresponding author.

Manuscript received September 3, 2018; final manuscript received February 28, 2019; published online March 22, 2019. Assoc. Editor: Dr. David G. Bogard.

J. Turbomach 141(8), 081006 (Mar 22, 2019) (11 pages) Paper No: TURBO-18-1232; doi: 10.1115/1.4043071 History: Received September 03, 2018; Accepted March 04, 2019

Recent advances in gas turbine film cooling technology such as round film cooling holes embedded in craters or trenches, and shaped film cooling holes are of interest due to a marked improvement in the effectiveness of film cooling jets. Typically, shaped film cooling holes have higher manufacturing cost, while film cooling holes embedded in craters/trenches etched in thermal barrier coatings (TBC) are seen as a cost-effective alternative. In a recent numerical study Kalghatgi and Acharya (2015, “Improved Film Cooling Effectiveness With a Round Film Cooling Hole Embedded in Contoured Crater,” ASME J. Turbomach., 137(10), p. 101006) reported a novel crater shape to generate anti-counter rotating vortex pair (CRVP) beneath the film cooling jet and showed a significant improvement in film cooling performance. In the present paper, a comprehensive study of flow dynamics is presented to gain insight into the unsteady flow physics of film cooling jet issued from a round hole embedded in the contoured crater. As a baseline case, a round film cooling hole with a 35 deg inclined short delivery tube (l/D = 1.75) is used as from a previous study with freestream Reynolds number based on jet diameter set to ReD = 16,000 and density ratio of coolant to freestream fluid of ρjo = 2.0. These flow conditions are used for the cases of film cooling jet embedded in contoured crater. The results are presented for two crater depths: (i) shallow crater with 0.2D depth and (ii) deep crater with 0.75D depth. First- and second-order flow statistics are presented for all the cases, including the experimental data for baseline case from the literature. Time-averaged and instantaneous flow structures are visualized to reveal the mechanisms of anti-CRVP and attenuating CRVP. The dynamics of flow structures studied using single-point spectral analysis in the shear layer and modal analysis of three-dimensional flow field shows a loss of coherency and increased time scales of shear layer structures as the crater depth is increased, primarily due to attenuating of CRVP in the downstream vicinity of the crater. The modal analysis confirmed reduced magnitude of temperature fluctuations (hot spots) on the cooling wall compared with baseline round film cooling hole. Finally, a 2–5% additional pressure loss due to the crater is reported over the existing ≈7% loss in pressure for baseline case.

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Figures

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Fig. 1

Schematic of contoured crater [31]

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Fig. 2

Schematic of near field coherent structures in the baseline round film cooling jet flow

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Fig. 3

Schematic of near field coherent structures in a film cooling jet flow issued from a round hole embedded in a contoured crater

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Fig. 4

Mean streamwise and wall-normal velocity profile comparisons of baseline and crater geometries (experimental data correspond to baseline round film cooling jet) (solid line, baseline u/UO (Sim); dashed line, baseline v/UO (Sim); solid triangle, baseline u/UO (Exp); inverted solid triangle, baseline v/UO (Exp); solid red line, 0.2D crater u/UO; solid green line, 0.4D crater u/UO; solid blue line, 0.75D crater u/UO; dashed red line, 0.2D crater v/UO; dashed green line, 0.4D crater v/UO; dashed blue line, 0.75D crater v/UO)

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Fig. 5

Mean streamwise velocity contours on a spanwise midsection

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Fig. 6

Mean wall-normal velocity contours on a spanwise midsection

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Fig. 7

Wall-normal velocity contours on an axial plane 0.5D downstream of the crater (streamlines indicate CRVP and anti-CRVP)

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Fig. 8

Comparison of RMS of streamwise and wall-normal velocity fluctuations for baseline and crater geometries (experimental data corresponds to baseline round film cooling jet) (solid line, baseline u′/UO (Sim); dashed line, baseline v′/UO (Sim); solid triangle, baseline u′/UO (Exp); inverted solid triangle, baseline v′/UO (Exp); solid red line, 0.2D crater u′/UO; solid green line, 0.4D crater u′/UO; solid blue line, 0.75D crater u′/UO; dashed red line, 0.2D crater v′/UO; dashed green line, 0.4D crater v′/UO; dashed blue line, 0.75D crater v′/UO)

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Fig. 9

Contours of RMS of streamwise velocity fluctuations on the spanwise midplane

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Fig. 10

Contours of RMS of wall-normal velocity fluctuations on the spanwise midplane

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Fig. 11

Flow structure in stationary flow field for 0.2D crater

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Fig. 12

Interaction of tornado vortex with CRVP (contours of streamwise vorticity)

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Fig. 13

Streamlines through the tornado vortex (contours of wall-normal vorticity)

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Fig. 14

Instantaneous temperature (left) and spanwise vorticity (right) for baseline and crater cases

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Fig. 15

Frequency power spectrum of the shear layer for baseline and crater cases (the streamwise velocity signal recorded near the upstream edge of the film cooling hole)

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Fig. 16

Growth rates of various dynamic modes for the crater geometries (0.75D—left), (0.2D—right). Growth rate of shear layer model for the baseline is shown for comparison.

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Fig. 17

Instantaneous flow structures colored with spanwise vorticity component for baseline case (left) and shear layer dynamic mode @ 3180 Hz (right)

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Fig. 18

Instantaneous flow structures colored with spanwise vorticity component for crater with 0.2D depth (left) and shear layer dynamic mode @ 1200 Hz (right)

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Fig. 19

Instantaneous flow structures colored with spanwise vorticity component for crater with 0.75D depth (left) and shear layer dynamic mode @ 965 Hz (right)

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Fig. 20

Instantaneous flow structures for the baseline round film cooling jet showing the development of CRVP (contours of streamwise vorticity)

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Fig. 21

Instantaneous flow structures for the 0.2D crater case showing the development of CRVP (contours of streamwise vorticity)

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Fig. 22

Instantaneous flow structures for the 0.75D crater case showing the development of CRVP (contours of streamwise vorticity)

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Fig. 23

Global energy spectrum for 0.2D (right) and 0.75D (left) crater

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Fig. 24

Energy spectrum of thermal modes on cooling wall 0.2D (right) and 0.75D (left) crater

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Fig. 25

Energy spectrum of thermal modes for baseline case; global energy spectrum (left) and energy spectrum on cooling wall

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Fig. 26

Low-frequency thermal modes corresponding to CRVP on cooling wall

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Fig. 27

Thermal modes corresponding to shear layer on cooling wall

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Fig. 28

Pressure loss coefficient for various crater depths

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Fig. 29

Contours of pressure loss coefficient on the spanwise midsection

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