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Handbook of Turbomachinery Second Edition Revised - Ventech!

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integration <strong>of</strong> multiple disciplines (aerodynamics and heat transfer)<br />

developed for the design <strong>of</strong> cooled gas turbine blades has been used. The<br />

blade model is simplified for the heat-transfer analysis by using 12 sections<br />

<strong>of</strong> the blade rather than the full 3D blade. All the above simplifications were<br />

incorporated in order to keep the computational effort at a reasonable level.<br />

However, it must be pointed out that the optimization framework can be<br />

easily adapted to include more detailed analyses, additional disciplines, and<br />

additional design objectives and constraints.<br />

Bezier–Bernstein polynomials for surface definition have been used to<br />

represent each <strong>of</strong> the 12 spanwise sections <strong>of</strong> the blade, leading to a<br />

relatively small set <strong>of</strong> design variables. Viscous blade-to-blade flow is<br />

calculated using the thin-layer 3D Navier–Stokes equations. The maximum<br />

and average temperatures at selected sections <strong>of</strong> the blade (obtained through<br />

a finite-element analysis) are minimized. The K–S function approach is used<br />

to solve the multiobjective constrained nonlinear optimization problem, and<br />

the results for the generic blade design show significant improvements in all<br />

the objective functions. The maximum and average temperatures at each<br />

section decreased considerably, resulting in a cooler blade. Design<br />

constraints such as fixed trailing-edge thickness and maximum thicknessto-chord<br />

ratio were satisfied. The maximum thickness-to-chord ratio<br />

constraint was found to be an active constraint, thus playing a major role<br />

in defining the external shape <strong>of</strong> the optimum blade.<br />

The topic addressed here is a relevant one in modern engineering<br />

design applications. The area <strong>of</strong> gas turbine blade design was used as a<br />

means <strong>of</strong> demonstrating the utility and the need for formal optimization<br />

procedures as integral elements <strong>of</strong> the overall design processes for various<br />

engineering applications. The benefits to be derived are enormous. The<br />

computational cost associated with the optimization process (not discussed<br />

here) is considerable for such a complex design application. However,<br />

computational tools are continuously improving in both efficiency and<br />

speed. Cleverly arranged configurations <strong>of</strong> computing resources (distributed<br />

computing, parallel algorithms, etc.) and a gradual scaling-up approach<br />

[starting with simpler models and gradually fine-tuning the models while<br />

eliminating design variables that do not impact the design very much (via<br />

sensitivity analysis)] will make such a process viable for practical<br />

applications.<br />

REFERENCES<br />

1. R. J. Goldstein, ‘‘Film Cooling,’’ Advances in Heat Transfer, Vol. 7, Academic<br />

Press, New York and London, pp. 321–379 (1971).<br />

Copyright © 2003 Marcel Dekker, Inc.

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