Boundary layer transition modeling on leading edge inflatable kite airfoils

Abstract

We present a computational fluid dynamic analysis of boundary layer transition on leading edge inflatable kite airfoils used for airborne wind energy generation. Because of the operation in pumping cycles, the airfoil is generally subject to a wide range of Reynolds numbers. The analysis is based on the combination of the shear stress transport turbulence model with the γ−trueR˜eθt transition model, which can handle the laminar boundary layer and its transition to turbulence. The implementation of both models in OpenFOAM is described. We show a validation of the method for a sailwing (ie, a wing with a membrane) airfoil and an application to a leading edge inflatable kite airfoil. For the sailwing airfoil, the results computed with transition model agree well with the existing low Reynolds number experiment over the whole range of angles of attack. For the leading edge inflatable kite airfoil, the transition modeling has both favorable and unfavorable effects on the aerodynamics. On the one hand, the aerodynamics suffer from the laminar separation. But, on the other hand, the laminar boundary layer thickens slower than the turbulent counterpart, which, in combination with transition, delays the separation. The results also indicate that the aerodynamics of the kite airfoil could be improved by delaying the boundary layer transition during the traction phase and tripping the transition in the retraction phase.

Identification of kite aerodynamic characteristics using the estimation before modeling technique

“…High‐fidelity models and flight simulators 7‐12 also play an important role during the design and optimization phases of the machines. Pioneering aerodynamic models 13‐15 have been followed by studies with viscous‐inviscid interaction methods, 16 Reynolds averaged Navier–Stokes simulations, 17,18 and large eddy simulations 19 . Most of the studies were dedicated to the analysis of leading edge inflatable and ram‐air kites at stationary flow conditions.…”

“…Pioneering aerodynamic models [13][14][15] have been followed by studies with viscous-inviscid interaction methods, 16 Reynolds averaged Navier-Stokes simulations, 17,18 and large eddy simulations. 19 Most of the studies were dedicated to the analysis of leading edge inflatable and ram-air kites at stationary flow conditions.…”

Three-Dimensional Unsteady Aerodynamic Analysis of a Rigid-Framed Delta Kite Applied to Airborne Wind Energy

“…Reduced order modeling techniques for the aerostructural optimization of morphing wings for AWE applications also used 3D steady VLM [17,18]. Steady Reynolds-Averaged Navier-Stokes (RANS) simulations were also used to study LEI kites in 2D [19] and 3D [6], and fluid structure interaction problems in 2D [20,21]. A 2D interactive boundary-layer approach was also proposed for a ram-air kite [22].…”

Public Responses to Airborne Wind Energy: A Literature Review

“…Once the kite has reached the maximum prescribed length of the tether, it is depowered and reeled back in, only to be instantly reeled out again, leading to a recurrent pumping cycle, which lasts a couple of minutes each (Figure 1). The pumping cycle of an airborne wind energy system consisting of a fixed ground station and a soft-wing kite flying crosswind manoeuvres [6].…”

“…Figure1. The pumping cycle of an airborne wind energy system consisting of a fixed ground station and a soft-wing kite flying crosswind manoeuvres[6].…”