The breastshot waterwheel: design and model tests

Breastshot waterwheels—that is, waterwheels where the water enters the wheel approximately at the level of the axis—were in widespread use in England and Germany during the nineteenth and early twentieth century. Although this type of wheel even today has the potential for the economical and environmentally acceptable exploitation of small hydropower with low heads from 1·5 to 2·5 m, very little is known about its performance characteristics. In order to assess the breastshot waterwheel for hydropower generation, a study of design methods and a series of model tests were conducted at Queen’s University Belfast. Sample calculations for a 4 m diameter wheel are given to explain the design principles. Tests on a 1:4 scale, 1 m diameter model gave efficiencies of 78·5% over a broad range of flows. Based on these measurements and observations, improved geometries for in- and outflow were developed, resulting in maximum efficiencies of 87·3%. An initial ecological assessment indicated that waterwheels may have a significantly reduced ecological impact when compared with turbines. The breastshot waterwheel was found to be an efficient and ecologically acceptable hydraulic energy converter with the potential for further development.