Aerodynamic Design and Study of a Vaneless Counter-Rotating Power Turbine with a High Output Power Ratio

The Vaneless Counter-Rotating Turbine (VCRT) is a novel aerodynamic layout that eliminates the guide vanes of the second stage, resulting in reduced axial size and weight, also decreased aerodynamic losses associated with them. Motivated by these advantages, a power turbine of this type was designed in this paper for a small aircraft with counter-rotating propfan. Firstly, the entire engine thermodynamic cycle was designed, and obtained the requisite parameters of the power turbine. Furthermore, the velocity triangle method was employed to the aerodynamic design of the VCRT. Three-dimensional simulation was performed at the design-point, and the performance showed that the total efficiency was 84.28%, the output power ratio κ was 2.8 and total output power was 9586.74W, which met the design requirements. Performance variations were obtained by further investigation on a wide range of operating conditions, including rotating speed and pressure ratio. The results showed that on the low pressure ratio condition, higher efficiency can be achieved by increasing the output power ratio κ with a constant rotating speed, which provided a reference for the development of such kind turbines for a small aircraft.