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TECHNICAL PAPERS

A Comparative Study of DES and URANS for Flow Prediction in a Two-Pass Internal Cooling Duct

[+] Author and Article Information
Aroon K. Viswanathan

High Performance Computational Fluids—Thermal Sciences and Engineering Lab, Mechanical Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060

Danesh K. Tafti

High Performance Computational Fluids—Thermal Sciences and Engineering Lab, Mechanical Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060dtafti@vt.edu

The x value corresponds to the x locations from a previous study (26) and is different from the notation used in the current study.

J. Fluids Eng 128(6), 1336-1345 (Apr 14, 2006) (10 pages) doi:10.1115/1.2353279 History: Received September 03, 2005; Revised April 14, 2006

The capabilities of the detached eddy simulation (DES) and the unsteady Reynolds averaged Navier-Stokes (URANS) versions of the 1988 k-ω model in predicting the turbulent flow field in a two-pass internal cooling duct with normal ribs is presented. The flow is dominated by the separation and reattachment of shear layers; unsteady vorticity induced secondary flows and strong streamline curvature. The techniques are evaluated in predicting the developing flow at the entrance to the duct and downstream of the 180deg bend, fully developed regime in the first pass, and in the 180deg bend. Results of mean flow quantities, secondary flows, and the average friction factor are compared to experiments and large-eddy simulations (LES). DES predicts a slower flow development than LES, whereas URANS predicts it much earlier than LES computations and experiments. However, it is observed that as fully developed conditions are established, the capability of the base model in predicting the flow is enhanced by the DES formulation. DES accurately predicts the flow both in the fully developed region as well as the 180deg bend of the duct. URANS fails to predict the secondary flows in the fully developed region of the duct and is clearly inferior to DES in the 180deg bend.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Schematic diagram representing the two pass channel used in the study and the grid in a unit rib region. The numbers 1–25 represent the blocks used for spatial averaging. (b) Grid distribution in rib pitch.

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Figure 2

Comparison of the fully developed flow and heat transfer characteristics downstream of the rib as predicted by DES for various grid densities. The x-axis correspond to the x locations from a previous study under fully developed condition (26) and is different from the notation used in the current study.

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Figure 3

Comparison of the fully developed flow and heat transfer characteristics downstream of the rib as predicted by LES (18) and DES (26). The x-axis correspond to the x locations from previous studies under fully developed conditions (18,26) and is different from the notation used in the current study.

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Figure 4

Comparison of streamlines in the developing region through a plane passing through the center z plane

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Figure 5

Comparison of u velocities in the developing region through the center z plane. Flow is from left to right.

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Figure 6

U velocities at a plane passing through the rib: (a) experiments Rau (31), P∕e=9; (b) LES—fully developed region (rib 6); (c) DES—fully developed region (rib 6); and (d) URANS—fully developed region (rib 6)

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Figure 7

Comparison of the streamwise velocities at y∕e=0.1 with experimental data, rib location x=5.45–5.55 (blank space in the plot)

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Figure 8

Comparison of w velocities in the developing region through a plane near the side wall. Streamwise flow is from left to right.

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Figure 9

Secondary flow in the duct measured at y∕e=1.5 and z∕Dh=0.45

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Figure 10

Secondary flow in the fully developed region of the duct (between ribs 9 and 10): (a) LES, (b) DES, and (c) URANS. The horizontal axis represents the spanwise direction and the vertical axis represents the normal direction.

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Figure 11

Iso-surfaces of instantaneous coherent vorticity (vorticity magnitude=4.0) predicted by DES and URANS in the developing regions of the duct. Black arrows represent the flow at the inlet.

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Figure 12

Comparison of the flow predicted by DES and URANS in the 180deg bend

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Figure 13

Secondary flow at the center of the 180deg bend. DES predicts Dean vortices impinging on the inner and outer walls, whereas URANS fails to predict these vortices.

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Figure 14

Schematic diagram of the lines where the measurements have been presented (top). Velocities in the center of the 180deg bend in comparison to experiments by Sewall (21) (bottom).

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Figure 15

Block-averaged friction factors in the complete channel

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