Basic Analysis of Counter-Rotating Turbines

A comprehensive basic analysis for various counter–rotating turbines is given with the blade element stage assumption. Similar to the classical analysis of common turbine stages, the appropriate independent variables and evaluation criteria of the counter–rotating turbine stages are first presented and then three typical kinds of rotating blade rows are defined and all possible typical schemes of counter–rotating turbine stages are enumerated. Their performances of specific work, load factor distribution between two counter–rotating shafts and efficiency are analysed and discussed for different shaft rotating speed ratios. This information is useful for the selection and preliminary design of a counter–rotating turbine. From the analysis results, it is concluded that the load capacity per unit engine length of counter–rotating turbines can be much higher than that of common turbines (approximately twice) without efficiency penalty or even with higher efficiency. Some triple counter–rotating turbines suitable for three shaft gas turbine power plants are proposed and analysed briefly too.