Steady-state RANS simulation of a leading edge inflatable wing with chordwise struts

Abstract

A crosswind pumping kite power system is an Airborne Wind Energy (AWE) system that uses a flying tethered device for energy generation through a ground-based generator. The AWE research group of the TU Delft was one of the first to demonstrate the functioning of such a system. The spin-off Kitepower later on continued the technological development of this concept towards a commercial product. The system uses a leading edge inflatable (LEI) wing that operates by alternating between a traction phase and a retraction phase. Throughout these phases, the wing experiences a wide range of flow conditions with frequently changing incoming flow velocity, angle of attack and sideslip angle. As the wing is made of a flexible membrane, the shape of the wing is not fixed and will change under the aerodynamic loads applied to it. Therefore, the aerodynamic optimisation of such a wing forms a complex Fluid-Structure Interaction (FSI) problem. However, this thesis will only focus on the aerodynamic analysis of the LEI V3A wing developed by Kitepower. The analysis is done through the use of steady-state Computational Fluid Dynamics (CFD) simulations with a rigid wing geometry. Similar work that was done previously used a simplified wing geometry, which omitted the chordwise struts and only considered a limited range of flow conditions. In this study, these struts have been included in the geometry and their impact on the aerodynamic performance is assessed. In addition to this, the aerodynamic performance of the LEI wing under sideslip conditions is analysed. A hybrid meshing approach has been adopted to generate the computational domain. Simulations have been performed using a Reynolds-Averaged Navier-Stokes (RANS) solver with transition model. Comparison of the force coefficient curves showed that the impact of the struts on the total aerodynamic performance is minimal. Throughout the whole range of flow conditions considered, the force coefficient curves showed similar trends and absolute values. Locally, there are differences in the flow fields, predominantly in the tip region on the pressure side of the wing. The change in aerodynamic performance as a function of the sideslip angle was concluded to be strong. An increase in the sideslip angle led to a drop in the lift coefficient and an increase in the drag coefficient. Averaged values of the force coefficients were in line with inputs of several numerical models. Comparison of the results to available experimental data showed agreement for a limited range of flow conditions. The differences between the results of the present study and available experimental data are believed to be caused by the experimental data processing methods, in-flight deformation of the wing and steering actuation.