Analysis of the characteristics of counter-rotating impellers of an active-type axial turbine stage at different circumferential velocity ratios

The paper analyzes the main operating characteristics of coaxial impellers of an active-type axial turbine stage operating in counter-rotation at different circumferential velocity ratios. The study was carried out to ensure the coordinated operation of counter-rotating impellers and the two auxiliary mechanisms driven by them, which makes it possible to reduce the total number of drive units. Optimal values of the outlet angles of the blade rows corresponding to the maximum efficiency of the turbine stage were obtained. It was found that an increase in the circumferential velocity of the second impeller relative to that of the first impeller leads to a decrease in the optimal outlet angles of the blade rows, with the most pronounced decrease observed for the second blade row. In the course of the study, the circumferential velocity ratio of the counter-rotating impellers was varied by changing the circumferential velocity of the second impeller. In this case, the external characteristics of the first impeller as functions of the speed characteristic remained unchanged, while the characteristics of the turbine stage varied due to the parameters of the second impeller. The effect of the circumferential velocity ratio on the optimal speed characteristic of the turbine stage and the second impeller was determined. The obtained power and torque performance indicators can serve as a basis for selecting auxiliary mechanisms driven by counter-rotating impellers in the design of ships and their power plants.

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