Multi-Fidelity Computational Aerodynamic Framework for the Static and Dynamic Behavior of Rigid Framed Delta Kites for Airborne Wind Energy
Creators: name: Castro-Fernández, Iván
name: Cavallaro, Rauno
name: Schmehl, Roland
name: Sánchez-Arriaga, Gonzalo
Publisher: name: Zenodo
Year: 2023

description: The development of Airborne Wind Energy (AWE) systems can benefit from computational aerodynamic models with different levels of fidelity. For instance, fast potential-flow methods can predict the average aerodynamic force and moment coefficients over Leading Edge Inflatable (LEI) [1] and Rigid-Framed Delta (RFD) kites [2]. At a higher-fidelity level, Reynolds-Averaged Navier-Stokes (RANS) simulations demonstrate to reliably represent the inherent flow separation in a LEI kite [3]. However, the aerodynamic response of AWE systems during figure-of-eight maneuvers is also characterized by hysteretic phenomena as recently revealed in an experimental campaign that included onboard flow measurements [4]. Being able to predict such a phenomenon with computational tools is of foremost importance for a correct prediction of AWE system performance. This work aims to model the static and dynamic aerodynamic behavior of RFD kites applied to AWE with three different levels of fidelity (Fig. 1). The first model (1) is an in-house Unsteady Panel Method (UnPaM) [2] that models the three-dimensional aerodynamic surface with an unsteady vortex lattice method and sheds a force-free wake. The second model (2) solves the unsteady incompressible RANS equations with the k-omega SST turbulence model through the open-source SU2 framework [5]. In our current setup, this finite volume Computational Fluid Dynamics (CFD) tool employs Arbitrary Lagrangian Eulerian dynamic meshing capabilities to adapt the volumetric mesh to the imposed motion of the RFD kite. The third model (3), which has a degree of fidelity and computational cost between (1) and (2), is a semi-empirical dynamic stall model that involves 4 building blocks: (i) attached flow, (ii) leading edge separation, (iii) trailing edge separation and (iv) leading edge vortex. Block (i) uses UnPaM to represent the 3D attached-flow behavior. Blocks (ii-iv) are governed by a set of phenomenological dynamic equations that have free empirical parameters. Such parameters were fine-tuned by using the results of the CFD data from tool (2). Steady analyses with the potential-flow tool (1) and the CFD tool (2) are compared concluding that flow separation and wake geometry are the main drivers of the discrepancies. The experimental kinematic conditions of the dynamic figure-of-eight maneuvers from Ref. [4] were prescribed in tools (1), (2) and (3). The hysteretic behavior found in Ref. [4] was qualitatively well captured only by tools (2) and (3). However, the quantitative differences suggest experimental uncertainties and/or underlying aeroelastic phenomena. Future works will aim at including aeroelastic effects into the current framework. <strong>References</strong> Leuthold, R. Multiple-Wake Vortex Lattice Method for Membrane-Wing Kites. Technical Report. Delft University of Technology: Delft, The Netherlands (2015). Castro-Fernández, I., Borobia-Moreno, R., Cavallaro R., Sánchez-Arriaga G. Three-Dimensional Unsteady Aerodynamic Analysis of a Rigid-Framed Delta Kite Applied to Airborne Wind Energy. <em>Energies</em> 14 (23) (2021). Viré, A.; Lebesque, G.; Folkersma, M.; Schmehl, R. Effect of Chordwise Struts and Misaligned Flow on the Aerodynamic Performance of a Leading-Edge Inflatable Wing. <em>Energies</em>, 15, 1450 (2022). Borobia‐Moreno, R., Ramiro‐Rebollo, D., Schmehl, R. and Sánchez‐Arriaga, G. Identification of kite aerodynamic characteristics using the estimation before modeling technique. <em>Wind Energy</em> 24 (6), 596-608 (2021). Economon, T. D., Palacios, F., Copeland, S. R., Lukaczyk, T. W. and Alonso, J. J. SU2: An Open-Source Suite for Multiphysics Simulation and Design. AIAA Journal, 54 (3) (2016).