Aerodynamics design of two-stage vaneless counter-rotating turbine

Vaneless counter-rotating turbine technology is one of the most efficient ways to greatly improve aero-engines performance. As the axial velocity ratio of high-pressure turbine rotor is much larger than conventional one, the optimal selection of counter-rotating turbine velocity triangles by theoretical analysis is developed, and how effect of high-pressure turbine stator/rotor outlet flow angle on the efficiency is also figured out. The key point to design a high efficient practicable vaneless counter-rotating turbine is to select velocity triangles that charactered by low flow coefficient, high outlet flow angle and large axial velocity ratio of high-pressure turbine rotor. In blade design, the convergent-divergent throat passage is necessary. The curvature of blade suction surface and the radius of trailing edge circle should be carefully selected while generating convergent-divergent blade by Bezier.