Comparison of Partial Admission Axial and Radial Inflow Turbines for Underwater S-CO2 Power Cycle System

Abstract

The reasonable application of supercritical carbon dioxide(S-CO2) power cycle systems to unmanned undersea vehicles(UUVs) can help address the problem of low efficiency for the existing UUV steam power cycle systems, especially for small-power applications. In order to select the optimal turbine for the underwater S-CO2 system, the one-dimensional approach combined with the loss model was used to obtain the best geometric parameters within the design space. In addition, the three-dimensional numerical simulation method based on the RANS equation was adopted to verify the rationality of the one-dimensional design method. The aerodynamic performance and flow characteristics of the axial/radial turbine were further compared. The results show that the internal efficiency of the radial turbine is 5.41% higher than that of the axial turbine under the design conditions, but the size of the radial turbine is larger, about twice that of the axial turbine. The main loss of the radial turbine is from the nozzle and the rotor non-working section, while that of the axial turbine is mainly concentrated in the secondary flow losses generated at the rotor. Through the analysis of variable operating conditions, it is found that the axial turbine is more suitable for the low velocity ratio operating conditions. Nevertheless, the radial turbine has higher efficiency at the same speed. This research can provide a reference for the development of the S-CO2 system power unit applied in UUVs.

Keywords

• unmanned undersea vehicle
• axial and radial turbine
• supercritical carbon dioxide
• aerodynamic performance