Vertical Axis Wind Turbines
In the presence of ever visible effects of global climate change, small scale wind turbines are considered as viable renewable systems. Horizontal axis wind turbines (HAWT) are popular for grid-connected power generation. Yet there is an increasing demand for small-scale portable power generation, typically away from the grid and provided by diesel generator and small scale photovoltaic panels. Small scale vertical axis wind turbines (VAWT) can be used as power supplies for telecommunication towers, recreational and military camps away from the population. Moreover silent and aesthetic VAWT prototypes are attractive for urban use as well. Unlike HAWTs, VAWTs are omnidirectional and can obtain higher capacity factors in near-the-ground installations where the direction of the wind is more erratic than higher altitudes.
There are two types of VAWT designs: drag-based and lift-based. In the drag-based Savonius design, drag force on the blades is asymmetric and wherever the wind blows the imbalance of forces yield a net torque on the rotor. Drag-based turbines are usually very low in aerodynamic efficiency. Lift-based Darrieus-type VAWTs can have higher efficiencies up to the Betz limit in high angular velocities of the rotor, which comes in different shapes.
The VAWT design that we are working on has the following features: an efficient blade profile and the chord length obtained from CFD simulations coupled with the dynamics of the rotor; blades that are made of cheap light-weight and durable composite materials for; and a model-based con-troller for maximum energy generation for given wind conditions. Generic turbulence models such as k-epsilon and k-omega are used in the time-dependent two-dimensional CFD models coupled with the dynamics and control of the rotor to obtain an optimum design. The profiles that satisfy aerodynamic efficiency requirements are built from shell-spar-foam type composite materials. Static and dynamic structural analysis of the blades and other components of the rotor such as the shaft and the arms are conducted to obtain appropriate profiles of the beams used in the design.