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Research Papers

# Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels—Part II: Experimental Validation

[+] Author and Article Information
Filippo Coletti

e-mail: coletti@vki.ac.be

Tom Verstraete

e-mail: tom.verstraete@vki.ac.be

Tony Arts

e-mail: arts@vki.ac.be
von Karman Institute for Fluid Dynamics,
Turbomachinery and Propulsion Department,
Chaussée de Waterloo 72,
Rhode-Saint-Genèse 1640, Belgium

1Present address: Mechanical Engineering Department, Stanford University, Stanford, CA.

2Present address: Tractable Engineering, Brussels, Belgium.

3Present address: Geosea NV, Zwijndrecht, Belgium.

4Present address: Techspace Aero, Milmort, Belgium.

Contributed by the International Gas Turbine Institute of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received January 22, 2012; final manuscript received October 25, 2012; published online June 28, 2013. Editor: David Wisler.

J. Turbomach 135(5), 051016 (Jun 28, 2013) (10 pages) Paper No: TURBO-12-1007; doi: 10.1115/1.4023031 History: Received January 22, 2012; Revised October 25, 2012

## Abstract

This two-part paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter, as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In the first part of the paper, the design methodology of the cooling channel was presented. In this second part, the optimized design is validated. The results obtained with the numerical methodology described in Part I are checked against pressure measurements and particle image velocimetry (PIV) measurements. The experimental campaign is carried out on a magnified model of a two-legged cooling channel that reproduces the geometrical and aerodynamical features of its numerical counterpart. Both the original profile and the optimized profile are tested. The latter proves to outperform the original geometry by about 36%, in good agreement with the numerical predictions. Two-dimensional PIV measurements performed in planes parallel to the plane of the bend highlight merits and limits of the computational model. Despite the well-known limits of the employed eddy viscosity model, the overall trends are captured. To assess the impact of the aerodynamic optimization on the heat transfer performance, detailed heat transfer measurements are carried out by means of liquid crystals thermography. The optimized geometry presents overall Nusselt number levels only 6% lower with respect to the standard U-bend. The study demonstrates that the proposed optimization method based on an evolutionary algorithm, a Navier–Stokes solver, and a metamodel of it is a valid design tool to minimize the pressure loss across a U-bend in internal cooling channels without leading to a substantial loss in heat transfer performance.

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## References

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## Figures

Fig. 1

Schematic representation of the experimental set up

Fig. 2

U-bend geometries for the standard (up) and optimized (down) configuration

Fig. 3

Inlet velocity profile across the center of the duct: comparison between experimental and numerical results

Fig. 4

Location of the measurement planes: static pressure (XZ planes) and PIV (XY planes). The location of the inlet velocity profile coincides with the one of the inlet static pressure measurement (magenta).

Fig. 5

Mean velocity from PIV in the standard geometry at Z/Dh = 0.5 (up) and at Z/Dh = 0.03 (down)

Fig. 6

Turbulent kinetic energy from PIV in the standard geometry at Z/Dh = 0.5

Fig. 7

Mean velocity from CFD in the standard geometry at Z/Dh = 0.5 (up) and at Z/Dh = 0.03 (down)

Fig. 8

Turbulent kinetic energy from CFD in the standard geometry at Z/Dh = 0.5

Fig. 9

Mean velocity from PIV in the optimized geometry at Z/Dh = 0.5

Fig. 10

Turbulent kinetic energy from PIV in the optimized geometry at Z/Dh = 0.5

Fig. 11

Mean velocity from CFD in the optimized geometry at Z/Dh = 0.5

Fig. 12

Turbulent kinetic energy from CFD in the optimized geometry at Z/Dh = 0.5

Fig. 13

Pressure distributions along the inner and outer wall at Z/Dh = 0.5 for the standard (up) and optimized (down) geometry

Fig. 14

Acceleration parameter at Z/Dh = 0.5 along the inner wall (up) and the outer wall (down)

Fig. 15

Normalized Nusselt number distributions on the bottom wall for the standard geometry (left) and the optimized geometry (right)

Fig. 16

3D view of the normalized Nusselt number distributions for the standard geometry (top) and the optimized geometry (bottom)

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