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Applied Computational Fluid Dynamics Techniques - Wiley Episode 2 Part 10

Tham khảo tài liệu 'applied computational fluid dynamics techniques - wiley episode 2 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 472 APPLIED COMPUTATIONAL FLUID DYNAMICS TECHNIQUES 20.7. Representation of surface changes The representation of surface changes has a direct effect on the number of design iterations required as well as the shape that may be obtained through optimal shape design. In general the number of design iterations increases with the number of design variables as does the possibility of noisy designs due to a richer surface representation space. One can broadly differentiate two classes of surface change representation direct and indirect. In the first case the design changes are directly computed at the nodes representing the surface line points Bezier points Hicks-Henne Hicks and Henne 1978 functions a set of known airfoils wings hulls discrete surface points etc. . In the second case a coarse set of patches is superimposed on the surface or embedded in space . The surface change is then defined on this set of patches and subsequently translated to the CAD representation of the surface see Figure 20.9 . Movement Surface Deformation of Movement Surface New CFD Domain Surface Figure 20.9. Indirect surface change representation CFD Domain Surface 20.8. Hierarchical design procedures Optimal shape design and optimization in general may be viewed as an information building process. During the optimization process more and more information is gained about the design space and the consequences design changes have on the objective function. Consider the case of a wing for a commercial airplane. At the start only global objectives measures and constraints are meaningful take-off weight fuel capacity overall measures sweep angle etc. Raymer 1999 . At this stage it would be foolish to use aRANS or LES solver to determine the lift and drag. A neural net or a lifting line theory yield sufficient flow-related information for these global objectives measures and constraints. As the design matures the information shifts to more local measures thickness chamber twist angle local wing .