<title>Active skin for turbulent drag reduction</title>

Abstract

Drag reduction for aerial vehicles has a range of positive ramifications: reduced fuel consumption with the associated economic and environmental consequences, larger flight range and endurance and higher achievable flight speeds. This work capitalizes on recent advances in active turbulent drag reduction and active material based actuation to develop an active or "smart" skin for turbulent drag reduction in realistic flight conditions. The skin operation principle is based on computational evidence that spanwise traveling waves of the right amplitude, wavelength and frequency can result in significant turbulent drag reduction. Such traveling waves can be induced in the smart skin via active-material actuation. The flow control technique pursued is "micro" in the sense that only micro-scale wave amplitudes (order of 30mm) and energy inputs are sufficient to produce significant benefits. Two actuation principles have been proposed and analyzed. Different skin designs based on these two actuation principles have been discussed. The feasibility of these different actuation possibilities (such as Shape Memory Alloys and Piezoelectric material based actuators) and relative merits of different skin designs are discussed. The realization of a mechanically actuated prototype skin capable of generating a traveling wave, using a rapid prototyping machine, for the purpose of validating the proposed drag reduction technique is also presented.

A Method for Reducing the Drag of the Ship Shaped Wall by Using Piezoelectric Ceramic Vibrators

“…The piezoelectric actuator has been applied in various filed thanks to the advantages of high accuracy, good controllability and fast response [15]- [18]. The working mechanisms of drag reduction based on piezoelectric vibration for plate structures are mainly discussed [19]- [21], while, to the best of our knowledge, the characteristics when applying this method on actual physical model are rarely discussed.…”

SMA-thin film composites providing traveling waves

“…Since shape-memory alloys (SMAs) provide large work output and since the workability of thin SMA films has been proved within the last 12 years 4 , SMA films are a suitable active element for adaptive structures and active skins. Lagoudas et al recently investigated the applicability of SMA wires for turbulent drag reduction 3 . The results of their calculations lead to the conclusions that turbulent drag reduction for unmanned aerial vehicles can be realized by surface waves with wavelengths of about 25 mm, an amplitude of 30 µm and a frequency of 50 Hz.…”

“…One main benefit of these structures is the influence of traveling surface waves on the friction properties of objects moving through a fluid and the applicability of such structures for turbulent drag reduction 3 . Additionally, in robotics, traveling waves are convenient for different motion concepts of mobile robots or for the transport of small components in fabrication process.…”