Flowfield and Pressure Measurements in a Rotating Two-Pass Duct With Staggered Rounded Ribs Skewed 45Degrees to the Flow

[+] Author and Article Information
Tong-Miin Liou

Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan, ROCtmliou@pme.nthu.edu.tw

Y. Sian Hwang, Yi-Chen Li

Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan, ROC

J. Turbomach 128(2), 340-348 (Mar 01, 2004) (9 pages) doi:10.1115/1.2162180 History: Received October 01, 2003; Revised March 01, 2004

Laser-Doppler velocimetry and pressure measurements are presented of the local velocity and wall pressure distributions in a rotating two-pass square duct with staggered ribs placed on the leading and trailing walls at an angle of 45deg to the main stream. The ribs were square in cross section with the radii of rounds and fillets to rib height ratios of 0.33. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are documented in terms of the evolutions of both main flow and cross-stream secondary flow, the distributions of the pressure coefficient, and the variation of friction factor with Ro. For CFD reference, the periodic fully developed flow condition is absent for the present length of the rotating passage roughened with staggered 45deg ribs. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are addressed. Using these relationships the general superiority of heat transfer enhancement of the staggered 45deg ribs arrangement over the in-line one can be reasonably illustrated. Simple expressions are obtained to correlate the friction factor with Ro, which are lacking in the published literature for passages ribbed with staggered 45deg ribs. The staggered 45deg ribs are found to reduce the friction loss to about 88%±1% of the in-line 45deg ribs for the rotating passage under the same operating conditions. The respective contributions of the angled ribs and passage rotation on the passage friction loss are identified.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Sketch of configuration, coordinate system, and dimension of test section

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Figure 2

Schematic drawing of flow system and LDV apparatus

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Figure 3

Longitudinal mean velocity and turbulence intensity profiles at inlet reference station X*=11.6 of the first pass in (a) Y*=0 (mid-plane) and (b) Z*=−0.5 planes.

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Figure 4

Examination of periodic fully developed condition by comparing U∕Ub profiles at XN∕H=3.5 in various pitches for Ro=0.15

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Figure 11

Friction factor versus rotation number (Re=10,000, Tr=trailing, Le=leading)

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Figure 12

Distribution of centerline transverse mean velocity near the 180deg turn for the cases (a) in-line 45deg ribs and (b) staggered 45deg ribs at Ro=0.15

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Figure 5

Evolution of longitudinal mean velocity component in Z*=−0.5 and Z*=0.5 planes

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Figure 6

Mean velocity vector plots around the turn for Re=1.0×104 and Ro=0.15 in X-Y plane of the (a) first and (b) second passages

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Figure 7

Mean velocity vector plot on the mid-turn cross-section (Z**=0) for Re=1.0×104 and Ro=0.15

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Figure 8

Distributions of transverse mean velocity on the cross-sectional planes near the entrance, around the 180deg turn, and near the exit for Ro=0.2 (dotted and solid arrows stand for Ωx generated by the ribs on the leading and trailing wall, respectively)

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Figure 9

Relationships between mean velocity components, turbulent kinetic energy, and regional averaged surface heat transfer coefficient

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Figure 10

Variation of dimensionless wall pressure with X∕DH at various rotation numbers (+ and ×: measured along the outer and inner side walls of the up and down passes, respectively)



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