Strength Design and Numerical Analysis of Radial Inflow Turbine Impeller for a 100kW Microturbine

Microturbines usually require a type of radial inflow turbine due to the need for high efficiency under the condition of small mass flow rate and compact geometry. This paper describes the strength design for a 320kW radial inflow turbine impeller during the research and development of 100kW class microturbine. The turbine has a high rotating speed up to 61000rpm and its inlet gas temperature reaches 900°C. Firstly, conventional method is adopted to design the impeller, but the maximum stress predicted by Finite Element Analysis (FEA) greatly exceeds the yield limit of material. In order to satisfy strength requirement of the impeller, the thickness, the inlet and outlet angles of blade in impeller are taken as parameters to optimize its geometry. Meanwhile, aerodynamic performance of blade and factors of manufacture are taken into account. With the aid of numerical analysis and optimization, an optimal impeller is obtained with a very low maximum stress of 651MPa, which can satisfy the strength requirement of the working impeller. The FEA results also show that the optimization method developed in this paper is a successful one, it can not only provide an optimal geometry for impeller and decrease its apparent stress, but also be much useful for strength design of other components of the machines. At last, aerodynamic performance of optimal impeller is analyzed by CFD and the numerical results shows it is satisfactory design.