Dielectric-barrier discharge plasma actuators were mounted on a circular cylinder in a square wave pattern for active forcing of the cylinder wake. The intermittent spacing of the buried electrodes created a spanwise modulated blowing profile, such that three-dimensional instabilities in the wake were targeted for control. Two distinct power levels of 5.6 and 13.6 watts were used for forcing the flow. Considerable spanwise variation in the wake was achieved with the lower power forcing when the actuators were mounted at the location of maximum shear layer receptivity. This spanwise variation was a direct consequence of the difference in the vorticity levels of the shed vortices from the cylinder. High power forcing nearly eliminated vortex shedding, leading to considerable amount of drag reduction as measured in the far wake. Nomenclaturewire voltage 2 f = frequency f st = vortex shedding frequency L = length along the actuator (spanwise direction) Re = Reynolds number t = time T s = period of vortex shedding u = fluctuating component of U ũ = periodic component of u u = random component of u U = streamwise velocity component U  = freestream velocity U j = plasma actuator jet velocity U = streamwise velocity component U = mean of streamwise velocity component v = fluctuating component of V V = transverse velocity component V = mean of transverse velocity component x = streamwise direction y = transverse direction z = spanwise direction  = spanwise wavelength of actuator ω z = spanwise vorticity

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Different stages of droplet generation are reported in this paper with two immiscible liquids, silicone oil and deionized water, inside a flow-focusing device for hydrophobic and hydrophilic channel walls. Hydrophobic and hydrophilic channels of identical geometry are compared. In this first set of experiments, the efficacy of the hydrophobic channel is compared with a square cross junction for a continuous oil phase with low viscosity. In the hydrophobic case, the flow-focusing design with a diverging outlet delays jetting and allows for the use of higher flow rate ratios in the squeezing regime. For the hydrophilic case, stable and well-structured droplet and slug generation can be achieved using oil and water, resulting in an inverse emulsion. However, the morphology of the fluid interface displays an unusual behavior compared to that of a hydrophobic microchannel. The droplet generation in the hydrophilic channel occurs following the formation of single and double T-junctions, a phenomenon hitherto unreported in the literature. The results demonstrate that the uncoated hydrophobic channels generate monodisperse droplets at a higher capillary number when compared to the hydrophilic channels.

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