Introduction to Aircraft Aeroelasticity and Loads

19

Potential Flow Aerodynamics

The two-dimensional strip theory aerodynamics that has been used so far in this book, for convenience, implies a number of major assumptions about the aerodynamic load distribution (e.g. neglects tip effects) and is only moderately accurate for low speed, high aspect ratio and unswept wings. Of particular importance is the assumption that the aerodynamic forces acting on one chord wise strip have no effect on other chord wise strips. In order to perform a more accurate aeroelastic analysis, aerodynamic theories need to be developed that are able to define more accurate pressure distributions over the entire wing. The so-called three-dimensional panel methods were developed to model the interaction between the aerodynamic forces on different parts of the lifting surfaces (wings, fin and horizontal tail surfaces) more accurately. It will be shown in Chapter 20 how it is possible to couple fully the panel method aerodynamics with a finite element (FE) model; consequently, panel methods are the primary aerodynamic tool used by industry for aeroelastic analysis. However, it should be noted that panel methods cannot be used to give accurate lift distributions in the transonic flight regime and corrections based upon wind tunnel tests are often employed. Also only the induced drag is able to be estimated. Consequently, there is an increasing use of higher fidelity computational fluid dynamics (CFD) methods, often solving the full Navier–Stokes equations, ...