14.7 Summary

improve the results – this is an area where experience is beneficial. Once the CFD is set up to yield good results, it is useful to improve and/or modify an aircraft configuration through extensive sensitivity studies. The spectrum plots in color show the hot spots that contribute to drag (e.g., local shocks and separation). These details cannot be seen as easily by any other means. Designers can follow through by repairing the hot spots to reduce drag. These opportunities are unique to CFD, making it an indispensable tool for optimizing a configuration for minimum drag. Any significant difference between the CFD and semi-empirical results should be investigated properly.

14.7 Summary

CFD simulation is a digital–numerical approach to design incorporated in the virtual-design process using computers. The current status is adequate for comparative analyses at low cost and time; therefore, it must be applied early in the conceptual design phase as soon as a CAD 3D model drawing is available. The development of CFD is not necessarily driven solely by aerodynamic considerations but rather by the requirement to have a tool to design a better product at a low cost and in less time.

CFD continues to develop with greater computing power at lower cost and in less time along with advances made in the algorithms for resolving solutions, providing considerable ease and automation to benefit users. Although researchers have achieved a degree of accuracy in drag prediction for a clean aircraft configuration, the generalized application by engineers is yet to achieve consistency in results. Verification and validation of results from CFD analysis are essential for substantiation, and the state of the art is still being scrutinized and continuing to develop. Verification of new CFD software comes before validation; together, they involve a protracted process in which research continues.

As a conservative user, the industry must ensure fidelity in a design. However, CFD is capable of comparison to recognize the better designs, even if the absolute values remain under scrutiny. This capability produces the best compromise in an early phase of the project at low cost and in less time, thereby avoiding subsequent costly modifications of an aircraft configuration – that is, it provides the opportunity to make the design right the first time. The design is subsequently tested in a wind tunnel for substantiation. Today, this approach requires few changes to the design after the final flight-test results.

The industrial effort in CFD is extensive and is not suitable for an undergraduate course. However, coursework can follow the industrial approach by solving smaller problems, such as those described in this chapter.