Erf2011-135 Geometric Optimisation of a Gurney Flap Hinge-less Deployment System for a Helicopter Model Blade

Following a comparative study on shape morphing and adaptive systems to improve rotorcraft efficiency, the Green Rotorcraft consortium has selected the Gurney flap technology as demonstrator of a smart adaptive rotorblade within the Clean Sky Joint Technology Initiative [1]. The aim of such a system is to actively increase helicopter overall performance by improving lift and alleviating static and dynamic stall on the retreating side of the helicopter [2, 3]. The Gurney flap technology will be subjected to various tests, prior to manufacturing a full-scale demonstrator. Along with wind tunnel and whirl tower tests on full blade sections, a reduced-scale blade is required to be tested on a rotary support in a wind tunnel. The aim is to have a fully operational mechanism in a 1/8th-scale blade. A specific system needs to be designed for this smaller model blade. The specifications for the model blade mechanism are more challenging compared to the full model blade. The blade tip speed must remain the same between the two blades. Therefore, the model blade rotation speed and centrifugal loads greatly increase. Piezoelectric patch actuators combined with flexible beams are chosen to design a fast and robust mechanism, which would fit inside the model blade and support the large centrifugal loads. A mechanism is modeled using Finite Element Analysis tools and its geometry is optimised using a surrogate optimisation to maximise displacement and force. The optimised geometry has a Z-shape profile and maximise displacement and force. The force generated is sufficient to counter directly the force of the airflow on the flap. However, the displacement and the mechanical work are not large enough to deploy directly the Gurney flap as a conventional flap. The deployment time remains insufficient as well. Building on these results, refined geometries are under investigation using the same optimisation process. INTRODUCTION Shape morphing and adaptive systems appear to be promising technologies for improving rotorcraft performances and efficiency [3–6]. The Green Rotorcraft Consortium have reviewed active concepts in the scope of the European Clean Sky Joint Technology Initiative to improve helicopter transportation on the following aspects: fuel consumption and performances, active vibration control and active noise control [7]. The Gurney flap technology was selected as a demonstrator of a smart adaptive rotorblade [1]. The Gurney flap consists in a small flap, which length measures typically 2% of the chord length, placed at of the rotorblade’s trailing edge as shown in Figure 1. It improves the lift of the blade at a small drag penalty. Overall, the lift over drag coefficient increases over a large range of angles of attacks [2, 3, 8]. Moreover, the Gurney flap alleviates the static and dynamic stall of the blade [9]. Gurney flap Chord line Chord length Figure 1: Sketch of a profile with a 2% long gurney flap at the trailing edge.