Active skin for turbulent drag reduction

Drag reduction for aerial and underwater vehicles has a range of positive ramifications: reduced fuel consumption, larger operational range, greater endurance and higher achievable speeds. This work capitalizes on recent developments in direct numerical simulation (DNS) studies on turbulent drag reduction techniques and active material based actuation to develop an 'active'skin for turbulent drag reduction. The skin operation principle is based on computational evidence from DNS studies indicating that spanwise traveling surface waves of the right amplitude, wavelength and frequency can result in significant turbulent drag reduction. Such traveling waves can be induced in the skin via active material actuation. The flow control technique pursued is 'micro' in the sense that only microscale wave amplitudes (order of 30 mum) and energy inputs are expected to produce significant benefits. In this work, a generalized actuation principle that can generate a traveling surface wave is proposed and analyzed. Two actuation schemes, that are approximate implementations of this generalized actuation principle, are considered. Treating these actuation schemes as design paradigms, several skin designs are developed. The feasibility of the different actuation possibilities, such as shape memory alloys and piezoelectric material based actuators, and the relative merits of the different skin designs are discussed. The feasibility studies include analytical solutions based on geometric idealizations, that are further refined using quasistatic finite element analysis. The dynamic responses of the skin designs to complicated loading sequences are investigated using dynamic finite element analysis. Rayleigh damping is used in the dynamic analysis to model the total damping present in the system.