Constructal paddle design with “fingers”

Here, we show how the performance of a paddle that pushes a fluid can be increased by making parallel slits through it. The slit spacing is varied to see its effect on the drag force and the maximum stress in the paddle. The effect of water speed and paddle dimensions is documented. Designs with one or more slits are investigated. The drag force is maximum when the slit spacing matches the boundary layer thickness of the flow through the slit. Furthermore, the drag force is greater when the slit spacing is nonuniform: larger in the central slits than in the peripheral slits. The paddle with slits of one size performs almost as well as the best design with nonuniform spacings. The paddle design with slits achieves the same drag force and maximum stress with less material compared with a paddle without slits.