A Lorentz Force Actuator for Skin Friction and Noise Reduction in Turbulent Flows Past AUVs

Objectives:1. To demonstrate experimentally at least thirty percent turbulent drag reduction using transverse traveling wave actuation.2. To fabricate Lorentz actuators based on electromagnetic tiles that produce the desired traveling waveforms.3. To quantify corresponding noise reduction in flat plate boundary layers and bodies of revolution.4. To quantify the net power savings for AUV implementation corresponding to different amounts of drag reduction.Methodology:In this proposal, novel arrays of electromagnetic tiles will be designed which will be attached to a flat plate and a body of revolution. Various waveforms will be tested that propagate along the transverse flow direction, and the amount of drag reduction and surface pressure fluctuations will be measured directly and indirectly using PIV, LDV, and force balance. The experimental design will be guided by existing as well as direct numerical simulations of turbulence.Rationale:Recent numerical results that the PI published in Science (vol 288, p. 1230, 2000) showed that turbulence could be suppressed effectively by enhancing properly the streamwise vorticity instead of attempting to weaken it, as has been attempted previously. This new idea can be implemented in the ocean environment using Lorentz force actuators, which will introduce the proper sources of vorticity. This technique will be particularly suitable for AUVs, also surface ships, with large surface area and corresponding large skin friction.