Numerical Investigation at Nominal and Off-Design Operations Of a Supersonic Turbine for Liquid Rocket Engines With Full and Partial Admission Nozzles

Abstract In recent years, various types of liquid rocket engines have been developed to achieve different types of mission, and modern rocket engines are required to operate at different conditions depending on flight situations such as launch and landing. Thus, rocket engines are required to be more reliable and robust. One of the key components for a rocket engine to enable flexible operating conditions is a turbine since it determines a power of feed-line systems and an efficiency of rocket system itself. To fulfill the requested output of the entire systems, an appropriate design of the turbine, including the selection of full/partial admission configurations, is of crucial importance. On the other hand, the development of supersonic turbines in turbo-pumps remains a challenge due to their complex internal flow structures and systems with high rotational speed. Furthermore, it is necessary to achieve high performance and stable operations under extensive operating range in respect of innovative transport technologies including the development of reusable launch vehicles. However, detailed flow characteristics at off-design conditions of supersonic turbines are yet to be fully understood. Therefore, this paper aims to study internal flow characteristics and performance of a supersonic turbine at different operating points. The present study first demonstrates the comparisons of 3D RANS simulation results of the selected supersonic turbine (JAXA subscale M-1 turbine) consisting of two stages with full admission nozzles and partial admission nozzles, where the experimental results with the partial admission configuration are available to validate the simulation results. The simulations are conducted with full stages and the entire circumferential configuration at 5 different operating conditions defined by the velocity ratio (the ratio between the turbine rotational velocity and isentropic velocity at the turbine outlet) including the nominal condition. The internal flow structures under off-design operations for both full and partial admission nozzle configurations are investigated to address profound features of the flow field at off-design operations in a supersonic turbine. The analysis is furthermore extended to reveal the mechanisms of the energy loss by comparing the results of the full admission and two different configurations of the partial admission nozzles at different operating conditions. As a result, an empirical method to determine nozzle and ventilation loss curves based on velocity ratio is proposed, and also it is demonstrated that these curves can be applied to predict energy loss of various partial admission configurations at different operating conditions.