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Research Papers

# Influence of Channel Orientation on Heat Transfer in a Two-Pass Smooth and Ribbed Rectangular Channel $(AR=2:1)$ Under Large Rotation Numbers

[+] Author and Article Information
Michael Huh

Department of Mechanical Engineering, The University of Texas at Tyler, 3900 University Blvd., Tyler, TX 75701-6699

Jiang Lei

Department of Mechanical Engineering, Turbine Heat Transfer Laboratory, Texas A&M University, 3123 TAMU, College Station, TX 77843-3123

Je-Chin Han

Department of Mechanical Engineering, Turbine Heat Transfer Laboratory, Texas A&M University, 3123 TAMU, College Station, TX 77843-3123jc-han@tamu.edu

J. Turbomach 134(1), 011022 (Jun 01, 2011) (14 pages) doi:10.1115/1.4003172 History: Received August 01, 2010; Revised August 31, 2010; Published June 01, 2011; Online June 01, 2011

## Abstract

Experiments were conducted in a rotating two-pass cooling channel with an aspect ratio of 2:1 $(Dh=16.9 mm)$. Results for two surface conditions are presented: smooth and one ribbed configurations. For the ribbed channel, the leading and trailing walls are roughened with ribs $(P/e=10, e/Dh=0.094)$ and are placed at an angle $(α=45 deg)$ to the mainstream flow. For each surface condition, two angles of rotation $(β=90 deg,135 deg)$ were studied. For each angle of rotation, five Reynolds numbers $(Re=10–40 K)$ were considered. At each Reynolds number, five rotational speeds $(Ω=0–400 rpm)$ were considered. The maximum rotation number and buoyancy parameter reached were 0.45 and 0.85, respectively. Results showed that rotation effects are minimal in ribbed channels, at both angles of rotation, due to the strong interaction of rib and Coriolis induced vortices. In the smooth case, the channel orientation proved to be important and a beneficial heat transfer increase on the leading surface in the first pass (radially outward flow) was observed at high rotation numbers. The correlations developed in this study for predicting heat transfer enhancement due to rotation using the buoyancy parameter showed markedly good agreement with experimental data $(±10%)$. Finally, heat transfer under rotating conditions on the tip cap showed to be quite dependent on channel orientation. The maximum tip cap $Nu/Nus$ ratio observed was 2.8.

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## Figures

Figure 1

Gas turbine blade internal cooling channels and their applicable aspect ratios

Figure 2

Rotating arm assembly used to perform heat transfer experiments with the 2:1 aspect ratio test section

Figure 3

Drawing showing the flow channel geometry of the 2:1 aspect ratio test section

Figure 4

Test section view showing the copper plate region numbering convention

Figure 5

(a) Test section tip view showing location of heaters and wall naming convention and ((b) and (c)) test section view showing rotation angles studied

Figure 6

Comparison of entrance effects in smooth and ribbed stationary channels (AR=2:1) at Reynolds numbers of (a) Re=10 K and (b) Re=40 K

Figure 7

(a) Effect of rib on near wall flow separation, reattachment, and circulation and (b) rib induced secondary flow development

Figure 8

Conceptual views of rotation and rib induced secondary flows for (a) smooth β=90 deg, (b) smooth β=135 deg, (c) P/e=10β=90 deg, and (d) P/e=10β=135 deg

Figure 9

Conceptual view of flow through the ribbed two-pass channel connected by a sharp 180 deg turn

Figure 10

Streamwise Nu/Nuo ratio distribution under rotating conditions for Re=10 K: (a) smooth leading 90 deg, (b) smooth trailing 90 deg, (c) smooth leading 135 deg, and (d) smooth trailing 135 deg

Figure 11

Streamwise Nu/Nuo ratio distribution under rotating conditions for Re=10 K: (a) ribbed leading 90 deg, (b) ribbed trailing 90 deg, (c) ribbed leading 135 deg, and (d) ribbed trailing 135 deg

Figure 12

Tip cap Nu/Nuo ratios for all Reynolds numbers and rotational speeds

Figure 13

Rotation number and buoyancy parameter at the Reynolds numbers and rotational speeds tested

Figure 14

Effect of rotation number on leading, trailing, outer, and inner walls in regions 4 and 10

Figure 15

Effect of local buoyancy parameter on leading and trailing walls in first pass

Figure 16

Effect of local buoyancy parameter on tip cap surfaces

Figure 17

Effect of local buoyancy parameter on leading and trailing walls in second pass

Figure 18

Average Nu/Nus ratios on leading and trailing walls in first and second passes versus Bo

Figure 19

Average Nu/Nus ratios on outer and inner walls in first and second passes versus Bo

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