Effects of hub endwall geometry and rotor leading edge shape on performance of supersonic axial impulse turbine. Part I

Abstract

The paper focuses on methods for an efficiency increasing of supersonic axial impulse turbines. There was chosen the axial turbine stage with axisymmetric nozzles and mean diameter 103.5 mm as the base model for a numerical and experimental investigation.There were chosen two modifications of the base design to provide an efficiency increasing: modification of the rotor leading edge design and modification of the rotor hub endwall design.The effect of these two factors on the turbine efficiency was analyzed separately. A preliminary numerical investigation showed that the rotor hub endwall modification provided an efficiency increasing up to 2% in comparison with the base model. Meanwhile, modification of the rotor leading edge shape did not provided significant efficiency increasing in comparison with the base model. Klonowicz et al. (2014)). KEYWORDS SMALL-SCALED TURBINES, SUPERSONIC TURBINESSupersonic turbine stages for different purposes were widely investigated since 1955 up to nowadays. The earlier investigations were made mostly experimentally, while the latest studies are mostly computational. The advanced methods of characteristics are used to apply in case of supersonic vanes and rotor blades design, nevertheless, supersonic stage total-to-static efficiency tends to stay of about 0.4 -0.5.Tomas P. Moffitt (1958) studied a high-work stage for a rocket pump drive with an inlet rotor Mach number of 2 and aftermixing Mach number of 2.43. Divergent part of the nozzle was designed in accordance with supersonic design technics. A rotor design using the supersonic-vortexflow theory was performed. A boundary layer thickness value was included to the design method. According to the experiments, the total-to-static stage efficiency (0.414) was significantly below the preliminary estimated value (0.504).Louis J. Goldman (1972) performed a comparison of analytically predicted and experimentally obtained total-to-static stage efficiency values. The nozzle vanes and rotor blades design was performed in accordance with the method of characteristics for the isentropic flow of a perfect gas. Then the corrections were involved to the stage design, taking into account the displacement thickness. The nozzle vanes design was made in order to obtain aftermixing Mach number of 2.85 (Mach number in stationary frame at the rotor inlet). The actual value of total-to-static stage efficiency (0.39) was well below the preliminary estimated value (0.50). Author assumed that this was a consequence of an unexpected flow separation regions and laminar boundary layer losses.Anderson et al. (1998) investigated a two stages super/transonic axial turbine for a pump drive in the framework of "Vulcan 2" project. A stage pressure ratio was equal to 12 in the design point. Due to non-optimal stage load coefficient the total-to-total efficiency remained rather low (0.4).A supersonic single-stage axial turbine was numerically studied by . A pressure ratio was set as 5.33 for the investigated turbine. The method of characteristics was ap...