Aerodynamic design of an axial impulse turbine for the high-temperature organic Rankine cycle

This work presents the aerodynamic design of an 80 kW axial impulse turbine with siloxane MM as working fluid for high-temperature organic Rankine cycle (ORC) applications. Based on the conventional turbine design method, the 1D preliminary design and 3D numerical simulations under both design and off-design conditions are conducted. The numerical results agree well with the preliminary design. The total-to-total isentropic efficiency of the proposed turbine reaches 77.46% with the pressure ratio of 6.54 and rotational speed of 15000 rpm. It can remain a high level in a wide range of operating conditions, especially at high pressure ratios and low rotational speeds. By comparing the maximum decrease value of turbine efficiency depending on the relative tip clearance, the axial impulse turbine shows less sensitivity to the tip clearance than the conventional turbine. The appropriate cascade solidities for the stator and rotor are both higher than the recommended ranges for the conventional turbine, which provide the reference for the further design. Although the axial impulse turbine exhibits slightly lower efficiency than the other ORC turbines in the research, it features great advantages of low cost and wide application which allow the assessment for ORC practical applications.