AERODYNAMIC BUGS: CAN CFD SPRAY THEM AWAY?

Computational fluid dynamics (CFD) has become a standard design tool for modem sophisticated aircraft. This paper reviews design methods that were used for some existing jet transport aircraft at a time when the theoretical tools had very limited capability. Early designers combined available theory and empirical data with sufficient skill to develop highly succeeaful aircraft. They also overcame serious problems that sometimes arose only after first flight, problems due to aerodynamic phenomena that were not predicted. Some of these problems are discussed in detail in this paper. The question of whether modern CFD would have warned of these problems and provided the necessary solutions is addressed. It is concluded that in many cases the answer is negative. Comparisons between two dimensional CFD airfoil compressibility drag rise, converted to finite wing drag rise using simple sweep theory, and flight test results show good agreement. A rapid method of compressibility drag rise prediction based on two dimensional CFD results is suggested. The method will define the drag that can be expected if the wing designers do a proper job, thereby allowing early performance prediction. The actual design of the wing is a task for a three dimensional wing and body CFD code including viscous and shock wave effects.