Raising requirements for aircraft engine efficiency and fuel consumption level combined with strong restrictions to engine weight and geometrical dimension pose serious challenges for engineers who are working under the new generation of engine development. These tasks require brand new flow path design approaches. The usage of a counter-rotating turbine is one of the possible ways to successfully match all these requirements. Modern aerodynamic design computational and optimization methodologies allow to fulfil this task in the shortest period of time with the highest gain in turbine performances.

A counter-rotating turbine means that blade rows are joined to two shafts with opposite rotation direction and different rotation speeds. Vanes elimination in a counter-rotating turbine helps to solve three important tasks of turbine improvement:

• Increasing turbine efficiency by eliminating vanes and correspondingly losses in vanes;
• Decreasing turbine blading weight;
• Decreasing turbine axial length;

These improvements are impossible without such fundamental design changes.

In the current paper the steps of counter-rotating turbine aerodynamic design, optimization, and offdesign performances estimation are described. The comparison of traditional and counter rotating turbines integral and detailed thermodynamic performances are presented.

INTRODUCTION

Traditional axial turbine consists of stationary vanes (stators) and rotating blades rows consequently placed in the flow path. Vanes are guiding and accelerating the flow in the required direction and moving blades are converting kinetic energy of moving fluid into mechanical work on the shaft. An example of traditional axial turbine stage is presented in the figure below.

Figure 1. Traditional axial turbine sketch