Design of double curvature radial turbine blades for a micro gas turbine

Abstract

The paper reports a study on the design of a radial turbine for a portable micro gas turbine engine. A unique design of blades with double curvatures is proposed which demonstrates the considerable advantage in terms of efficiency and power output. The design process largely consists of design, optimization, and analysis of radial turbine closely based on low mass flow rate and high-pressure ratio. The intention of the development is to achieve reductions both in fuel consumption and emissions. The micro gas turbine engine is designed to generate 20 kW net power output. As a 110 mm centrifugal compressor takes 56 kW power in the Brayton cycle, a 113 mm inlet diameter radial turbine is designed to produce 76 kW power. Optimization of the initial turbine geometry is carried out using an inverse design technique to improve the overall turbine stage performance. The original turbine blade meridional frame was used as an input to the optimization. The optimized 3-D blade geometry have a unique double curvature blade sections which is unlikely to be achieved using the conventional design approach. The performance of the optimized geometry has been compared with that of the initial geometry. Computational fluid dynamic and finite element analysis techniques were used for examining the aerodynamic performance and structural integrity respectively. The rotational speed of the turbine was set up to 101,400 RPM. The result of computational dynamic analysis indicates that the optimized geometry provides an approximately 6% increase in total-to-static efficiency on average and 6 kW increase in power output at high expansion ratio as compared to the original design. Stress analysis shows that the maximum stress is lower than the yield strength of the material, which verifies that the turbine design is mechanically viable.