Multiple Wake Vortex Lattice Method for Airborne Wind Energy Membrane-Wing Kites (poster)

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Multiple Wake Vortex Lattice Method for Airborne

Wind Energy Membrane-Wing Kites

Rachel Leuthold,

Roland Schmehl

r.c.leuthold@student.tudelft.nl, TU Delft Faculty of Aerospace Engineering

Figure 1: Wake Deformation on a Clark-Y-Profile Paraglider found with a Single-Wake VLM at α = −4o.

Problem Statement

The proper modelling of Fluid-Structure Interaction (FSI) effects (aeroelasticity) of LEI tube kites requires the aerodynamic sur-face pressure distribution on the wing. FSI modelling requires an aerodynamic model that is fast and accurate, but flow separa-tion is the primary source of modelling error when potential-flow models are applied to membrane wings like the LEI kite (Rojrat-sirikul et al, 2009).

With a measured range of angle of attack α of 50o and a ge-ometry containing a backwards-facing step, the degree of flow separation is significant though the kite does not exhibit the characteristic behavior of full-stall during normal operation.

Figure 2: Flow Separation Regions on the LEI Profile, and VLM_MW Vorticity Discretization into Vortex Rings

Multiple-wake potential-flow vortex models are well established to model flow separation for 3D rigid wings and for 2D membrane wings, leading to the hypothesis that a quasi-steady multiple-wake vortex lattice method (VLM_MW) can quickly and accurately model surf-kite aerodynamics to generate aerodynamic surface load distributions.

Multiple-Wake Vortex Lattice Method

Generate Geometry or Rearrange Inputs for Position and

Veloc-ity of Surface Points

Discretize Grid _{Initial Bound Circulation Strength} + Initial Wake Shape Assumption

+ Known Separation Locations

Convect Wake Nodes with Velocity at Downstream Node

Compute Vortex Core Size, including Filament Stretching

Compute Induction via Vatistas Core Model Use Normal Vectors to Determine Neumann BC

Compute New Bound Circulation Strength by Solving Boundary Condition

Split Circulation Strength between Wakes for

Conservation of Circulation

Convergence?

Sum Velocity on the Surface Nodes

Determine Loads and Pressure Distribution via Kutta-Joukowski

Surface Pressure Distribution

no yes

First Results:

Single-Wake Clark-Y-Profile Paraglider

−10 0 10 20 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 α [deg] CL [-] Single−Wake VLM 3D Viscous LLT (Leloup, 2014) STAR−CCM+ (Maneia, 2007) −100 0 10 20 30 0.05 0.1 0.15 0.2 0.25 α [deg] CD [-]