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Research Papers: Techniques and Procedures

Shape Optimization of a Multi-Element Foil Using an Evolutionary Algorithm

[+] Author and Article Information
Yu-Tai Lee

 Naval Surface Warfare Center, Carderock Division, West Bethesda, MD 20817yu.lee@navy.mil

Vineet Ahuja, Ashvin Hosangadi

 CRAFT Tech, Pipersville, PA 18947

Michael Ebert

 Naval Surface Warfare Center, Carderock Division, West Bethesda, MD 20817

J. Fluids Eng 132(5), 051401 (Apr 28, 2010) (11 pages) doi:10.1115/1.4001343 History: Received September 17, 2009; Revised February 19, 2010; Published April 28, 2010; Online April 28, 2010

A movable flap with a NACA foil cross section serves as a common control surface for underwater marine vehicles. To augment the functionality of the control surface, a tab assisted control (TAC) surface was experimentally tested to improve its performance especially at large angles of operation. The advantage of the TAC foil could be further enhanced with shape memory alloy (SMA) actuators to control the rear portion of the control surface to form a flexible tab (or FlexTAC) surface. Hybrid unstructured Reynolds averaged Navier–Stokes (RANS) based computational fluid dynamics (CFD) calculations were used to understand the flow physics associated with the multi-element FlexTAC foil with a stabilizer, a flap, and a flexible tab. The prediction results were also compared with the measured data obtained from both the TAC and the FlexTAC experiments. The simulations help explain subtle differences in performance of the multi-element airfoil concepts. The RANS solutions also predict the forces and moments on the surface of the hydrofoil with reasonable accuracy and the RANS procedure is found to be critical for use in a design optimization framework because of the importance of flow separation/turbulent effects in the gap region between the stabilizer and the flap. A systematic optimization study was also carried out with a genetic algorithm (GA) based design optimization procedure. This procedure searches the complex design landscape in an efficient and parallel manner. The fitness evaluations in the optimization procedure were performed with the RANS based CFD simulations. The mesh regeneration was carried out in an automated manner through a scripting process within the grid generator. The optimization calculation is performed simultaneously on both the stabilizer and the nonflexible portion of the flap. Shape changes to the trailing edge of the stabilizer strongly influence the secondary flow patterns that set up in the gap region between the stabilizer and the flap. They were found to have a profound influence on force and moment characteristics of the multi-element airfoil. A new control surface (OptimTAC) was constructed as a result of the design optimization calculation and was shown to have improved lift, drag, and torque characteristics over the original FlexTAC airfoil at high flap angles.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematics of TAC foil tested in the 0.61m (24 in) water-tunnel (a) overall foil (b) a cross section with defined angles

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Figure 2

Foil instrumented and actuated with SMA wires

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Figure 3

FlexTAC foil in the 0.91m (36 in) water-tunnel

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Figure 4

Force comparisons for TAC and FlexTAC foils

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Figure 5

Moment comparisons for TAC and FlexTAC foils

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Figure 6

Comparison of (a) water-tunnel paint traces and (b) closed-up traces with (c) predicted surface particle traces

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Figure 7

Flow of information in the design optimization loop

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Figure 8

A typical multi-element unstructured grid used in design optimization studies

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Figure 9

Design landscape showing relative performance of flap characteristics for all shapes utilized by the GA

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Figure 10

Flap lift comparison for C132 and C46

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Figure 11

Flap torque comparison for C132 and C46

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Figure 12

Comparison of the axial velocity distributions among (a) baseline, (b) C132 and (c) C46 designs with (d) the shed vortex in the flap nose region, which links with the reverse axial velocity distributions

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Figure 13

Comparison of the Cp distribution and shape profile of the C132 and baseline designs

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Figure 14

Comparison of the Cp distribution and shape profile of the C46 and baseline designs

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Figure 15

Comparison of forces between FlexTAC and OptimTAC foils (a) lift and (b) drag

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Figure 16

Comparison of moments between FlexTAC and OptimTAC foils (a) stabilizer torque and (b) flap torque

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