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Research Papers

Effects of Upstream Step Geometry on Axisymmetric Converging Vane Endwall Secondary Flow and Heat Transfer at Transonic Conditions

[+] Author and Article Information
Zhigang Li, Luxuan Liu

Institute of Turbomachinery,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China

Jun Li

Institute of Turbomachinery,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: junli@mail.xjtu.edu.cn

Ridge A. Sibold, Wing F. Ng

Department of Mechanical Engineering,
Virginia Polytechnic Institute and
State University,
Blacksburg, VA 24061

Hongzhou Xu, Michael Fox

Solar Turbines, Inc.,
San Diego, CA 92186

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 31, 2018; final manuscript received August 21, 2018; published online November 5, 2018. Editor: Kenneth Hall.

J. Turbomach 140(12), 121008 (Nov 05, 2018) (14 pages) Paper No: TURBO-18-1178; doi: 10.1115/1.4041294 History: Received July 31, 2018; Revised August 21, 2018

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5×106. A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88Cx (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward-facing step located just before the gap at 0.88Cx (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely, Nusselt number, was derived. This paper also presents a comparison with computational fluid dynamics (CFD) predictions performed by solving the steady-state Reynolds-averaged Navier–Stokes with Reynolds stress model using the commercial CFD solver ansysfluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25% to 0% span), and five backward-facing, upstream step geometries (step heights from 0% to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures and explain the effects of upstream step geometry. Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient (HTC) level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the HTC (by ∼10% to 40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3–1.3%) because of the forward-facing upstream step geometry but is slightly reduced (by 0.1–0.3%) by the presence of the backward upstream step geometry.

Copyright © 2018 by ASME
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Figures

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Fig. 1

Schematic view of the Virginia Tech Transonic Linear Cascade Wind Tunnel

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Fig. 2

Vane cascade with endwall

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Fig. 3

Inlet step and endwall geometries of two experimental cascades: baseline with no step (left) and misaligned configuration with step ΔH=6.78 mm (right)

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Fig. 4

Forward-facing and backward-facing upstream step and endwall geometries for CFD simulations

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Fig. 5

Computational model and mesh for the baseline cascade configuration

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Fig. 6

Comparison of measured (left) and predicted (right) endwall Nusselt number distribution: (a) baseline configuration (ΔH=0 mm) and (b) misaligned configuration (ΔH=6.78 mm)

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Fig. 7

Comparison of measured and predicted endwall Nusselt number along three streamlines: (a) baseline configuration (ΔH=0 mm) and (b) misaligned configuration (ΔH=6.78 mm). Figure 8 provides the streamlines locations.

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Fig. 8

Locations and labels of the streamlines along which the Nusselt number is extracted for heat transfer comparison

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Fig. 9

Endwall Nusselt number distributions predicted for five cascade configurations with backward-facing, upstream step geometries: (a) baseline configuration (ΔH=0 mm), (b) ΔH=3 mm, (c) ΔH=5 mm, (d) ΔH=6.78 mm, and (e) ΔH=10 mm

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Fig. 10

Endwall Nusselt number distributions predicted for four cascade configurations with forward-facing, upstream step geometries: (a) baseline configuration (ΔH=0 mm), (b) ΔH=−3 mm, (c) ΔH=−5 mm, and (d) ΔH=−8 mm

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Fig. 11

Nusselt number and relative Nusselt number predicted along three streamlines for five cascade configurations with backward-facing, upstream step geometries: (a) Nusselt number and (b) relative Nusselt number. Figure 8 provides the streamlines locations.

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Fig. 12

Nusselt number and relative Nusselt number predicted along three streamlines for four cascade configurations with forward-facing, upstream step geometries: (a) Nusselt number and (b) relative Nusselt number. Figure 8 provides the streamlines locations.

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Fig. 13

Near endwall streamline distributions (Nu contour background) predicted for five cascade configurations with backward-facing, upstream step geometries: (a) baseline configuration (ΔH=0 mm), (b) ΔH=3 mm, (c) ΔH=5 mm, (d) ΔH=6.78 mm, and (e) ΔH=10 mm

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Fig. 14

Spanwise streamline distribution predicted along plane A for five cascade configurations with backward-facing, upstream step geometries: (a) baseline configuration (ΔH=0 mm), (b) ΔH=3 mm, (c) ΔH=5 mm, (d) ΔH=6.78 mm, and (e) ΔH=10 mm. Figure 13(a) provides plane A position.

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Fig. 15

Near endwall streamline distributions (Nu contour background) predicted for four cascade configurations with forward-facing, upstream step geometries: (a) baseline configuration (ΔH=0 mm), (b) ΔH=−3 mm, (c) ΔH=−5 mm, and (d) ΔH=−8 mm

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Fig. 16

Spanwise streamline distribution predicted along plane A for four cascade configurations with forward-facing, upstream step geometries: (a) baseline configuration (ΔH=0 mm), (b) ΔH=−3 mm, (c) ΔH=−5 mm, and (d) ΔH=−8. Figure 15(a) provides plane A position.

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Fig. 17

Total mass-averaged loss coefficient versus upstream step height

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Fig. 18

Comparison of pitchwise mass-averaged loss coefficient for different upstream step geometry configurations: (a) backward-facing upstream step configuration and (b) forward-facing upstream step configuration

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