Davide Gatti

The dielectric breakdown limit of silicone dielectric elastomer actuators

Soft silicone elastomers are used in a generation of dielectric elastomer actuators (DEAs) with improved actuation speed and durability compared to the commonly used, highly viscoelastic polyacrylate 3M VHB™ films. The maximum voltage-induced stretch of DEAs is ultimately limited by their dielectric breakdown field strength. We measure the dependence of dielectric breakdown field strength on thickness and stretch for a silicone elastomer, when voltage-induced deformation is prevented. The experimental results are combined with an analytic model of equi-biaxial actuation to show that accounting for variable dielectric field strength results in different values of optimal pre-stretch and thickness that maximize the DEA actuation.

Performance losses of drag-reducing spanwise forcing at moderate values of the Reynolds number

A fundamental problem in the field of turbulent skin-friction drag reduction is to determine the performance of the available control techniques at high values of the Reynolds number Re. We consider active, predetermined strategies based on spanwise forcing (oscillating wall and streamwise-traveling waves applied to a plane channel flow), and explore via Direct Numerical Simulations (DNS) up to Reτ = 2100 the rate at which their performance deteriorates as Re is increased. To be able to carry out a comprehensive parameter study, we limit the computational cost of the simulations by adjusting the size of the computational domain in the homogeneous directions, compromising between faster computations and the increased need of time-averaging the fluctuating space-mean wall shear-stress. Our results, corroborated by a few full-scale DNS, suggest a scenario where drag reduction degrades with Re at a rate that varies according to the parameters of the wall forcing. In agreement with already available informatio...

Reynolds-number dependence of turbulent skin-friction drag reduction induced by spanwise forcing

This paper examines how increasing the value of the Reynolds number

Dynamic performance of silicone dielectric elastomer actuators with bi-stable buckled beams

Re

Global energy fluxes in turbulent channels with flow control

n affects the ability of spanwise-forcing techniques to yield turbulent skin-friction drag reduction. The considered forcing is based on the streamwise-travelling waves of spanwise-wall velocity (Quadrio etxa0al. , J. Fluid Mech. , vol.xa0627, 2009, pp.xa0161–178). The study builds upon an extensive drag-reduction database created via direct numerical simulation of a turbulent channel flow for two fivefold separated values of

Study of Energetics in Drag-Reduced Turbulent Channel Flows

Re

Turbulent skin-friction drag reduction at high Reynolds numbers

n , namely

Experimental assessment of spanwise‑oscillating dielectric electroactive surfaces for turbulent drag reduction in an air channel flow

Re_{unicode[STIX]{x1D70F}}=200

Turbulent Duct Flow Controlled with Spanwise Wall Oscillations

n and

Direct numerical simulation of controlled turbulent duct flows

Re_{unicode[STIX]{x1D70F}}=1000