Design and analysis of a 1.5 kW single-stage partial-admission impulse turbine for low-grade energy utilization

Turbines are widely used as the expanders in low-grade power systems. Increasing the expansion pressure ratio can improve the system efficiency whereas supersonic flow may occur inside the expander, increasing the turbine design difficulty. For small-scale power system, impulse turbine is a suitable option when the mass flow is small and the expansion pressure ratio is high. In this study, a 1.5 kW single-stage partial-admission impulse turbine is designed for waste heat recovery of internal combustion engines. The aerodynamic characteristics of the designed supersonic impulse turbine are analyzed. First, a preliminary design of the nozzle and the impeller is conducted based on the mean-line model and the main geometry parameters are obtained. Then, the blade profile is designed using the characteristic line method. A 3D CFD simulation is performed based on the designed impulse turbine and the flow field is analyzed under the design and off-design conditions. The results indicate that the mean velocity and the Mach number at the nozzle outlet arrive at 1082.87 m/s and 2.645, respectively. A high load is generated on the blades in the partial-admission region due to the pressure difference between the pressure and suction surfaces. The two blades in the middle output the largest torques, taking up nearly 48% of the overall torque. The output power of the turbine achieves 1.385 kW with a total-to-static efficiency of 42.52%. However, some special flow phenomena are found in the edges of the partial admission region such as the inverse flow and the endwall cross flow at the blade hub, the transverse forward flow at the blade tip. The shock wave at the leading edge of the flow channel and the expansion acceleration of the working fluid at the trailing edge are also observed. The results provide a reference for small-scale impulse turbine design with a small mass flow and a high pressure ratio.