This project is aimed at characterizing the flow physics associated with turbulent liquid flow over superhydrophobic surfaces of various topologies and explores the combined passive drag reducing mechanisms of riblets and superhydrophobicity. The benefits of riblets on reducing the drag in turbulent boundary layers have been long understood, while superhydrophobic surfaces have recently emerged as a different mechanism for drag reduction. The coupling of these two drag-reducing mechanisms has not previously been explored, and it is expected that their combined benefit will be much greater than can be achieved by either mechanism alone. The impact of such surfaces on minimizing flow resistance is far reaching, ranging from microfluidic applications to large-scale liquid flows. The main technical objectives of the work are to provide significant characterization of the flow of liquids over superhydrophobic surfaces with and without riblets and to quantify their effectiveness in reducing drag in turbulent flows. Experiments are conducted in a small-scale turbulent channel flow where particle image velocimetry is employed to provide detailed characteristics of the flow field, in both streamwise and transverse planes. Upon elucidation of optimal parameter ranges from the PIV testing, experiments in a water tunnel will also be conducted, where the total drag on flat plates tiled with test surfaces will be measured. In parallel with the experimental program, direct numerical simulations of turbulent channel flow with surfaces exhibiting riblets and slip are performed. These simulations do not replicate exact experimental conditions, but rather provide additional fundamental insight into the coupling of riblets, which suppress spanwise motions, and slip derived from supherhydrophobicity in both the spanwise and streamwise directions. This work influences students at all levels of the educational system. In addition to the formal involvement of PhD students, undergraduate students are active participants in the work. Further, the work is integrated into Brigham Young University Summer of Academic Refinement (SOAR) program. In SOAR, minority high-school students spend several summer weeks on the BYU campus preparing for college admission tests, experiencing university life, and learning about the different programs of study. The students participate in workshops at various laboratories around campus, including the cleanroom where the superhydrophobic test surfaces are fabricated. The experience of SOAR students is further augmented by lab activities and experiments that explain superhydrophobic surfaces and drag reduction.
