Relative roles of computational fluid dynamics and wind tunnel testing in the development of aircraft

Much is talked of Computational Fluid Dynamics (CFD), concerning its role in the possibility of bringing down the costs and turn-around times in the design and development of aircraft. Views have been expressed, at one extreme end, that wind tunnel testing may play a secondary role eventually. This communication takes a balanced view according to which both CFD and wind tunnels are inevitable; there are roles which are exclusive for CFD and wind tunnels and there are roles which are synergistic and complementary. Additionally, both CFD and wind tunnel testing are, after all, only tools whose optimality of usage is always as good as the experience and the relevant design database of the designer of the aircraft. It is argued here that the efficacy of CFD in aircraft design is to be judged not so much by the number of wind tunnel blow downs that can be saved as it is to be judged by the value addition to the design cycle by its contribution to a superior baseline for final tuning and check-out of configuration through detailed wind tunnel testing and by the guidance obtainable through rapid CFD simulations for better utilization of tunnel tests.