Computer Science in Partial Fulfillment of the Requirements for the Degree of Masters of Science in Electrical Engineering and Computer

Much of the current research in turbulent drag reduction centers on controlling locally individual streamwise vortices. These techniques involve complex closed loop control systems that become difficult or impossible to implement in practice. Extensive numerical simulation has suggested that introducing streamwise vorticity in the form of a transverse unsteady excitation can reduce drag far more effectively than spanwise vorticity control and would only require simple open loop control making it far easier to implement. In this work we implemented the above concept using Lorentz force actuators consisting of alternating pairs of electrodes and magnets. Specifically, we used a transverse oscillating square current waveform, and conducted experiments in a weakly conductive sodium nitrite solution. Detailed velocity profiles using laser Doppler velocimetry (LDV) were obtained in the 1 to 3 m/s range, and preliminary direct force measurements were made with piezoelectric force sensors. The primary findings of this work are: * Drag reduction of up to 37% was observed, in agreement with direct numerical simulations (DNS). * Input power was observed to vary inversely with flow speed. * Dependence of the effect on frequency was in agreement with DNS with the optimum period at about T=100. " Change in drag was observed to be non-monotonic with respect to current as predicted by DNS. * At higher speeds the amplitude range for which drag reduction occurred was observed to increase. " Electrode thickness, which influences the Lorentz force penetration depth into the fluid, was shown to not be as critical as suggested by DNS. " Conductive polymer coating of the electrodes was shown to dramatically reduce corrosion and electrolysis. These results are the first experimental manifestation of large turbulent drag reduction using electro-magneto-hydro-dynamic (EMHD) excitation. In addition, this work was done at speeds several times faster than any other previous EMHD experiments. They point to net power savings at speeds above about 8 m/s and to robustness of this approach for real world applications. Acknowledgements I would like to thank George Karniadakis, Chryssostomos Chryssostomidis, Richard Kimball, and Vasileios Symeonidis for helping me in the research and writing of this thesis. I would also like to thank my family and friends for their years of support and encouragement. In particular I can always count on Dawn and The one person I could never have done this without is my fiancee, Ann Gajewski. I will be forever grateful for the days of patience and understanding …