As it is clear from flow paths comparison applying counter-rotating allows to decrease axial length from 0.42 to 0.29 meters (by 30% approximately) and decrease total estimated mass of vanes and blades up to 40% approximately.

Initial and counter-rotating turbine rows view on mean station is presented in the figures below with velocity triangles.

Figure 6. Initial turbine rows and velocity triangles

Figure 7. Counter-rotating turbine rows and velocity triangles

Counter-rotating Design (6 stages). We found that counter-rotating design with 4-stage obtained for direct comparison of flow paths gives significant decrease in length and weight of turbine. Considering different design possibilities we assume that another variation of counter-rotating design with 6 stages is applicable and will not exceed initial axial sizes and mass limitations. 6- stage design was obtained by performing axial turbine design from scratch, removing vanes, smoothing meridional dimensions and inlet metal angles adjustment to match minimal incidence angle.