The effect of plasma actuator that uses saw-tooth or sine-wave shape electrodes on boundary layer flows is experimentally investigated. The measurement results are compared with a corresponding standard configuration (conventional design using two rectangular strip electrodes)-the actuator that produces a nearly two-dimensional horizontal wall jet upon actuation. PIV measurements are used to characterize the actuators in a quiescent chamber. Operating in a steady manner, the new actuators result in the formation of streamwise and spanwise vortices. That is to say, the new actuators render the plasma actuators inducing three-dimensional variations in the shear layer, offering significant flexibility in flow control. The affected flowfield with the new actuators is significantly larger than that with the conventional linear actuators. While the conventional linear actuators affect primarily the boundary layer flow on a scale of about 1 cm above the wall, the new actuators affect the near wall region at a significantly larger scale. This new design broadens the applicability and enhances the flow control effects and it is potentially a more efficient flow control device. flow control, plasma actuator, PIV

The three-dimensional fluid flow in a vertical bending continuous caster was numerically studied. Three dimensionless collision numbers were introduced to analyze the inclusion collision mechanism. The analysis showed that turbulent collisions were the major factor causing inclusions to collide with each other in the continuous caster. Stokes collisions had a minor effect and Brownian collisions were negligible. A mathematical model was then developed to study the inclusion collisions in the continuous caster. The mathematical model considered the inclusion mass transfer and expressed the radius and population of new inclusions after coalescence relative to the mass and population conservation. Since the motion of clustershaped inclusions differs from that of spherical inclusions, the inclusion physical parameters were modified. The results showed that the inclusions congregated approximately one fourth of the face width from the slab edge so that the characteristic radius distribution of the inclusions had a 'W' shape, while the inclusion concentration and number density had an inverse 'W' shape in the longitudinal direction. More inclusions were trapped near the inner arc and they had larger characteristic radii than those near the outer arc. The concentration and inclusion number density decreased with the distance from the free surface, but the inclusion radius increased.

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