Savonius Wind Generator and Alternator - ebook plan

Savonius wind generator including theory, detailed design and materials list with excellent photographs and description.

On the Performance of the Savonius Wind Turbine

An extensive wind tunnel test program is described which assesses the relative

influence of system parameters on the Savonius rotor performance. The

parametric study leads to an optimum configuration with an increase in efficiency

by around 100 percent compared to the reported efficiency of ≈ 12-15 percent.

Of particular interest is the blockage correction procedure which is vital for

application of the wind tunnel results to a prototype design, and facilitates

comparison of data obtained by other investigators. Next, using the concept of a

central vortex, substantiated by a flow visualization study, a semi empirical

approach to predict the rotor performance using measured stationary blade

pressure data is developed. The simple approach promises to be quite effective

in predicting the rotor performance, even in the presence of blockage, and

should prove useful at least in the preliminary design stages.

Introduction

The Savonius rotor concept never became popular, until recently, probably

because of its low efficiency. However, it has the following advantages over the

other conventional wind turbines:

- simple and cheap construction;

- acceptance of wind from any direction thus eliminating the need for

reorientation;

- high starting torque;

- relatively low operating speed (rpm).

The above advantages may not outweigh its low efficiency and make it an ideal

economical source to meet small scale power requirements, especially in the

rural parts of developing countries. ----- The concept of the Savonius rotor was

based on the principle developed by Flettner. Savonius used a rotor which was

formed by cutting the Flettner cylinder into two halves along the central plane

and then moving the two semicylindrical surfaces sideways along the cutting

plane so that the cross-section resembled the letter “S.” -----

The following are some rules for construction of a Savonius rotor.

a. The size of the end plates, to which are mounted the buckets, should

be about 5% larger than the diameter of the rotor.

b. The central shaft should be mounted to the end plates only, and not

through the buckets. By keeping the shaft to the end plates, the air

space is not blocked. For example, a central shaft of about 20% of the

rotor diameter reduces the power coefficient by about 8%.

c. The aspect ratio, height to diameter, 6 to 8 gives a better performance.

However, an aspect ratio of about 2 is desirable from the economic

point of view.

d. Use only two buckets, as a higher number reduces the efficiency.

e. The use of augmentation devices such as concentrators or diffusers or

combination of the two result in increased power coefficient. Again,

the increased costs of such devices should be weighed against the

increased capital cost and complexities.