No abstract

No abstract

The aim of this study was to assess the applicability of a numerical design tool for pitching airfoils; by evaluating their aerodynamic performance comparing experimental and numerical data at different levels of complexity. Experimental findings of non-harmonically pitching airfoil configurations in a water tunnel at medium Reynolds numbers are compared to solutions of a modified double-wake vortex-panel method with boundary-layer formulation and unsteady Reynolds-averaged Navier–Stokes simulations. For steady-state airfoil configurations at high angle of attack, large eddy simulation data are also considered. Rigorous analysis of the sources of error and uncertainty in numerical methods and measurements proves that from an engineering point of view, a low-cost double-wake model is well suited for the design process of, for example, wind-turbine blades. That is, the overall first-order error and uncertainty of the double-wake panel method with a strong viscous-inviscid interaction model are in a reasonable range against the measurements and the much more expensive numerical methods. Thus, the low computational costs plus the accuracy make the unsteady panel-boundary-layer method a useful and reliable tool to analyze the aerodynamics of pitching airfoils in the design process.

Vortex methods like vortex-lattice or vortex-panel methods are particularly promising to enhance the industrial aerodynamic design process of modern wind turbines. However, despite their advantages over low order methods, like the blade-element-momentum theory, vortex methods share an essential disadvantage. Their computational cost rapidly increases, which is due to their n-body problem characteristics. To overcome this issue, a method that neither relies on multipole expansions nor on a multi-grid approach is presented. Based on the aerodynamic simulation of the MEXICO rotor, it is shown that the proposed vortex pseudo-particle method (VPPM) is able to reduce the computational cost related to the n-body problem of vortex methods to O(n × log(n)). However, its application is not only advantageous in terms of the reduction of the computational cost. Since vortex-and pseudo-particles share the same properties, the VPPM’s implementation is quite simple compared to that of fast multipole methods. Furthermore, no method specific boundary-conditions need to be imposed as in the case of multi-grid methods. Therefore, the presented pseudo-particle approach is an attractive alternative to fast multipole or multi-grid methods.