A formal error analysis of the order of approximation of a potential based boundary element method (BEM) for two-dimensional flows is performed in order to derive consistent approximations for the potential integrals. Two higher-order approaches satisfying consistency requirements to attain second and third order convergence in the potential are selected for numerical implementation. From the formal local expansions of the potential integrals the influence coefficients are derived and evaluated analytically. In order to assess the methods accuracy, the low and higher-order methods are applied to two-dimensional steady flows around analytical foils. A numerical error analysis is done and a comparison between their theoretical and numerical asymptotic order of accuracy performed.
IntroductionBoundary element methods (BEM) have been used successfully for many years in the solution of compressible and incompressible inviscid flows around complex configurations, [8]. In the aerodynamic and hydrodynamic fields, these methods, also known as panel methods, have matured to a level which allows their use as design tools on a routine basis. In spite of the success achieved in many hydrodynamic applications, there are situations where BEM computations may still pose considerable challenges, both from the modelling and the computational points of view. This appears to be the case in the non-linear computations of partial and super-cavitating flows on hydrofoils and marine propellers, e.g. [10,12]. From the computational point of view, BEM solutions of such flow problems require the use of accurate and efficient numerical algorithms which need to be applied on considerably fine grids. Maskew, [13], has shown that the low-order potential based BEM, [9,15], was able to provide solutions for the pressure distribution with accuracy comparable to higher-order methods for a small number of panels. However, in non-linear computations of cavity flows on foils accurate solutions may only be obtained with a large number of elements, especially in regions of high geometry curvature, such as the leading edge and the cavity closure region, [2,5]. This still involves large computation times in the three-dimensional flow case, which makes its application in design studies rather time consuming. In such situations higher-order methods may become attractive to further reduce computation times.In the present paper, we concentrate on the application of higher-order boundary element methods to the twodimensional case of the steady incompressible potential flow around foils in the absence of cavitation. The work of Kinnas and Hsin [11] showed that the rate of convergence of the low-order BEM on foils is slow due to the effect of the local error on the sharp trailing edge. Therefore, significant improvements are expected from higher-order BEM formulations. Such improvements may turn out to be of practical relevance in the application of the method to the computation of 2D unsteady cavitating flows needed for design purposes. Our objective is to inv...