Numerical Study on Rotor-Stator Interaction of a Supersonic Reaction Turbine for a Liquid Rocket Engine

For an open cycle liquid rocket engine, such as the expander bleed cycle, the mass flow rate of turbine driving gas should be small, especially to improve rocket engine performance. However, work output must be high as possible. As a result, pressure ratio of the turbine becomes high, and Mach number at both nozzle exit and rotor inlet becomes supersonic. As a result, strong shock wave interaction can be generated between nozzle exit and rotor inlet, and this interaction affects the turbine aerodynamic performance. However, this rotor-stator interaction of supersonic turbine has not yet been clarified. Therefore, as the first step, it is important to clarify the structure of the flow field and to evaluate the accuracy of CFD method as practical engineering tool for liquid rocket engine design. In the present study, quasi 3-D RANS simulations were applied to the NACA supersonic turbine and the numerical results were compared with the experimental ones to evaluate numerical methodology. Turbulence models and rotor/stator interface modeling method were compared, and their impacts to the turbine aerodynamic performance estimation were evaluated. In addition to these points, the flow field between nozzle and rotor region and the turbine efficiency were investigated. The present results clarify some features of rotor-stator interaction. The shock wave, which is generated near the nozzle exit caused by encounter of nozzle exit flow, reflects at the neighbor nozzle wall and affects the rotor region. At the same time, the shock wave from the rotor leading edge impinges the nozzle cascade, and these shocks interact with each other. The present results showed that Mach number at nozzle outlet becomes different due to each turbulence and rotor/stator interface models. This difference of Mach number influences the shape of detached shock wave at the leading edge of rotor blade, and changes the entire rotor region flow field such as static pressure profile of rotor region. Thus, turbine efficiency may be influenced by these different features of flow field.