4. The Side View “3D” Model
The side view model is constructed in pseudo-3D by basing the frame on ellipses which act as tilted circles in Geometry Expressions, learn more about how this aspect of the semi-3d model is accomplished with this interactive figure. With this model, the traces give the appearance of an actual twisted Savonius turbine, and when we animate the X variable—which controls the spin—we can get an animation of the wind turbine operating in the wind as it would look from the side. The ability of Geometry Expressions to create semi-transparent surfaces out of traces allows us to see both blades as they are spinning which is especially useful for trying to study and understand the shape. It has been observed, and will be discussed in a later section, that as the Savonius wind turbine is twisted, its blades are squeezed (see figures at end of page). More specifically, a horizontal cross section of a twisted or untwisted Savonius wind turbine will always be a semicircle but the radius of that circle is smaller in the center than at the top and the bottom when the turbine is twisted. When the twist is 180 degrees, or pi radians, the turbine blade actually comes to a point. Because this is not at all realistic for an operational turbine, full size cross section “supports” are added and the turbine’s actual blade is really only twisted as much as 45 degrees between each support, making the squeeze minimal while still allowing for a full 180 degree twist. Remember that twisting 2 blades 180 degrees will allow for the wind to be “in contact” with the blade for the full 360 degree rotation, thus eliminating any chance for harmful pulsations. All of these considerations are built into the side view model. Play with the interactive version (complete, but without the traces) at right. View its entire construction and animation processes with detailed discussion at a moderate speed in video 1, or a 16x speed version in video 2.
Twisting Savonius VAWTs with and without cross-section supports: