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Research Papers

Analysis of Turbulent Flow in 180 deg Turning Ducts With and Without Guide Vanes

[+] Author and Article Information
Jiang Luo, Eli H. Razinsky

 Solar Turbines Incorporated, A Caterpillar Company, San Diego, CA 92101

J. Turbomach 131(2), 021011 (Jan 29, 2009) (10 pages) doi:10.1115/1.2987239 History: Received August 13, 2007; Revised May 05, 2008; Published January 29, 2009

This paper presents a numerical study of the turbulent flows through a number of 2D and 3D 180 deg U-ducts, with and without guide vanes, using the Reynolds-averaged Navier–Stokes method. Computations have been first carried out for a 2D U-duct flow (W/H=1.0) with four turbulence models (V2F, k-ε, shear stress transport (SST), and Reynolds stress). The models’ capability for predicting streamline curvature effects on turbulence and separation has been assessed, using flow and turbulence data. The effects of adding a guide vane inside the bend have been analyzed to reduce/avoid flow separation. Three vanes with different radial locations have been studied, and the mechanism for pressure loss reduction has been examined. Analyses have been performed for turbulent flows in 3D U-ducts with square cross section and sharp 180 deg turning (W/D=0.2), similar to the U-bends in typical turbine blade cooling passages. The predictions are compared with the data of outer-wall pressure. The effects of the guide vane and outer-wall shape on the flow separation, secondary-flow vortices, and pressure loss have been evaluated. The combined vane and uniform cross section area are found to improve the flow distribution and reduce the pressure loss significantly.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Mesh for 2D U-bend (Ri=0.5H, Ro=1.5H)

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Figure 2

Velocity (Vm/Ub) contours predicted by the models

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Figure 3

Predicted turbulence level (Tu) contours

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Figure 4

Profiles at 90 deg section: predictions versus data (y/H=0 at inner wall; y/H=1.0 at outer wall). (a) U/Ub and (b) Tu.

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Figure 5

Velocity (U/Ub) profiles at x=1H downstream

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Figure 6

Wall pressure (Cp) distribution through the bend: predictions versus data (S/H=0 at θ=0°; S/H=3.1 at θ=180 deg)

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Figure 7

Skin friction coefficients: predictions versus data: (a) inner wall and (b) outer wall

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Figure 8

Three flow guide vanes inside the U-bend: 50%, 34%, and 20% locations (measured from the inner wall)

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Figure 9

Predicted velocity (Vm/Ub) contours: without vane and with different vanes (all by the RSM)

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Figure 10

RSM-predicted turbulence level (Tu) contours: without and with different vanes

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Figure 11

Longitudinal velocity profiles at 180 deg section: RSM predictions without and with vanes versus data (without vane)

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Figure 12

Profiles at x=2H downstream of 180 deg section (S/H=5.1): RSM predictions (without and with vanes) versus data (without vane). (a) Longitudinal velocity and (b) turbulence level.

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Figure 13

Wall pressure distributions: RSM predictions (without and with vanes) versus data (without vane)

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Figure 14

Duct skin friction coefficients (Cf): RSM predictions (with and without vanes) versus data (without vane). (a) inner wall and (b) outer wall.

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Figure 15

Mesh for 3D U-Ducts without and with vane (Ri=0.1D)

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Figure 16

Predicted velocity contour (Vm/Ub) on symmetry section of the straight-corner duct: without and with vane

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Figure 17

Secondary-flow vectors on the sections inside the straight-corner duct: without and with vane

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Figure 18

Pressure distributions on the centerlines of inner and outer walls (x/D=0 at θ=90 deg), without and with vane: predictions versus data (Case 1 without vane; outer wall only)

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Figure 19

Velocity contour (Vm/Ub) on symmetry section of round-corner duct (Ri=0.1D, Ro=1.1D): without and with vane

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Figure 20

Secondary-flow vectors on sections in Case 4

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Figure 21

Decay of secondary-flow kinetic energy through the U-ducts (three sections: 90 deg, 1D and 2D downstream)

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Figure 22

Pressure on the centerlines of inner and outer walls (Cases 3 and 4): predictions versus data (Case 1; outer wall)

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