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Optimization and Computational Fluid Dynamics - Department of ...

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260 Marco Manzan, Enrico Nobile, Stefano Pieri <strong>and</strong> Francesco Pinto<br />

(a) (b)<br />

Fig. 8.22 Example <strong>of</strong> secondary vortices for the 3D NURBS channels: (a) extrusion angle<br />

<strong>of</strong> 20 ◦ ;(b) extrusion angle <strong>of</strong> 40 ◦<br />

f/f 0<br />

20<br />

15<br />

10<br />

5<br />

2D linear−piecewise<br />

2D NURBS<br />

3D linear−piecewise<br />

0<br />

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2<br />

Nu/Nu<br />

0<br />

Fig. 8.23 Pareto fronts: 2D-3D linear piecewise <strong>and</strong> 2D smooth NURBS pr<strong>of</strong>ile<br />

Therefore, a second, simpler optimization has been carried out using 5 design<br />

variables, by fixing W. Moreover the objective ∆T has been transformed<br />

to a constraint, in order to simplify the optimization <strong>and</strong> to favour module<br />

geometries with lower surface area <strong>and</strong> lower pressure drop. The optimization<br />

has been carried out for 332 designs. At this point the process was practically<br />

converged. The Pareto front <strong>of</strong> this optimization is reported in Fig. 8.24<br />

where it can be seen that the designs with the same inclination angle θ are<br />

rather perfectly aligned. A decrease <strong>of</strong> the inclination angle leads to lower

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