Electro-active polymer (EAP) “dimple” actuators for flow control: Design and characterisation.

Abstract

The long-term goal of this work is the development of a 'smart' skin capable of sensing and real-time actuation of oncoming turbulent flow, specifically to reduce skin-friction drag. Active "dimples" are time-dependent depressions that optimally alter local flow conditions [2]. Lightweight Electro-Active Polymers (EAPs) are ideal for these control surfaces since they offer high strain rate, fast response, low power consumption and ease of manufacture [13]. Key features for integration into a control system are robustness and repeatable, predictable motion. For this objective dimples are assessed and values for out-of-plane deflection, frequency response and vibrational modes, failure modes as well as power consumption values are presented. The dimple design comprises a buckling actuator, which can actuate without the need of a directional bias, differentiating itself from previous designs [16,17,18,19,20,21]. It also actuates from flush to the surface providing asymmetrical forcing, a key consideration for flow control purposes. It is shown that the dimple actuates with vibrational modes higher than the fundamental, and that these are non-linear, an important consideration for this type of device. The power consumption of the device, as required for net power savings, and device robustness is promising.

Turbulent friction drag reduction using electroactive polymer and electromagnetically driven surfaces

“…DEAs have been demonstrated to produce large strains, fast response times, O(µs), and high electromechanical efficiency (>90%). Such promising performance has been exploited and has led to numerous tentative applications including artificial muscles for robots, linear actuators, refreshable Braille systems and flow-control devices such as dimples, Dearing et al (2007) and Dearing et al (2010). These actuators, however, require high voltages to operate, O(3) kV, and the technology is still immature, often leading to fragile actuators with a high proportion of high-voltage burn-through failures.…”

Self-actuated snap back of viscoelastic pulsing structures

“…An example of such a system is the proposed use of repeatedly-actuated polymer dimples on the surface of a wing to enable substantial drag reduction, which in turn can improve fuel efficiency (Dearing et al, 2010). In this concept, in-plane actuation is applied periodically which causes the dimples to move back and forth.…”

Dynamics of viscoelastic snap-through

“…Similar to the phenomenon of creep buckling (Hayman, 1978), the total snap-through time is then governed by the viscous timescale of the material and can be very large. This phenomenon may be useful in morphing devices that are required to cycle continuously between two distinct states; for example, dimples proposed for aircraft wings that buckle in response to the air flow to reduce skin friction (Dearing et al, 2010;Terwagne et al, 2014), and ventricular assist devices which use snapthrough of a spherical cap under a cyclic pneumatic load to pump blood (Gonçalves et al, 2003). In these applications, pseudo-bistability means that the actuation needed to move the structure between different states can be applied for a shorter duration, which may lead to a significant reduction in the energy consumed (Santer, 2010).…”