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Research Papers: Forced Convection

# Heat Transfer in a Two-Pass Rectangular Channel $(AR=1:4)$ Under High Rotation Numbers

[+] Author and Article Information
Yao-Hsien Liu, Michael Huh

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

Je-Chin Han

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

Sanjay Chopra

Siemens Power Company, 4400 Alafaya Trail, Orlando, FL 32826

J. Heat Transfer 130(8), 081701 (Jun 02, 2008) (9 pages) doi:10.1115/1.2909615 History: Received June 15, 2007; Revised October 11, 2007; Published June 02, 2008

## Abstract

This paper experimentally investigated the rotational effects on heat transfer in a two-pass rectangular channel $(AR=1:4)$, which is applicable to the channel near the leading edge of the gas turbine blade. The test channel has radially outward flow in the first passage through a redirected sharp-bend entrance and radially inward flow in the second passage after a $180deg$ sharp turn. In the first passage, rotation effects on heat transfer are reduced by the redirected sharp-bend entrance. In the second passage, under rotating conditions, both leading and trailing surfaces experienced heat transfer enhancements above the stationary case. Rotation greatly increased heat transfer enhancement in the tip region up to a maximum Nu ratio $(Nu∕Nus)$ of 2.4. The objective of the current study is to perform an extended parametric study of the low rotation number (0–0.3) and low buoyancy parameter (0–0.2) achieved previously. By varying the Reynolds numbers (10,000–40,000), the rotational speeds $(0–400rpm)$, and the density ratios (inlet density $ratio=0.10–0.16$), the increased range of the rotation number and buoyancy parameter reached in this study are 0–0.67 and 0–2.0, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the two-pass, 1:4 aspect ratio flow channel.

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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 1:4 aspect ratio test section

Figure 3

Drawing showing redirected sharp-bend entrance and the flow channel geometry of the 1:4 aspect ratio test section

Figure 4

Test section view showing the copper plate region numbering convention

Figure 5

Stationary Nusselt number distribution in each region of the channel

Figure 6

Nu ratio (Nu∕Nu0) comparisons for different entrance geometries in a smooth channel

Figure 7

Conceptual view of (a) rotation-induced secondary flow inside a two-passage rectangular channel (AR=1:4), and (b) turn-induced secondary flow

Figure 8

Streamwise Nu ratio (Nu∕Nu0) distributions for different rotational speeds

Figure 9

Nu ratio (Nu∕Nus) distribution with respect to the rotation number in Regions 4 and 10

Figure 10

Nu ratio (Nu∕Nus) with respect to the rotation number in the tip region

Figure 11

Nu ratios (Nu∕Nus) with respect to buoyancy parameter from Regions 1 to 4

Figure 12

Nu ratios (Nu∕Nus) against buoyancy parameter from Regions 5 to 8

Figure 13

Nu ratios (Nu∕Nus) with buoyancy parameter from Regions 9 to 12

Figure 14

Average Nu ratios (Nu∕Nus) (six points) in the first pass

Figure 15

Average Nu ratios (Nu∕Nus) (six points) in the second pass

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