AbstractThe article discusses the stress optimisation process of the highly loaded disc of a high-speed radial-axial microturbine. At the design stage, the strength optimisation is vitally important for these types of devices because they must withstand very high temperatures (600∘C in this case) and be capable of operating at high rotational speeds (96,000 rpm in this case). Calculations were made using a three dimensional FE numerical model. The optimisation process is strictly connected with the choice of materials — which in this case are Inconel 738 (nickel-cobalt super alloy) and silicon nitride. Several stress reduction methods were developed, which took into account the mass of the disc, the rotational speed of the rotor and the complex shape of the rear part of the disc. Numerical computations helped to choose the best optimisation method, which decreased maximum reduced von Mises stresses by about 45% (from 1,288 MPa to 705 MPa). The methods proposed in this article are universal and can be implemented in the design process of various high-speed radial-axial microturbines. This article could be of interest to scientists and engineers who deal with highly loaded microturbines, which are increasingly used in many industrial sectors.

The article discusses the mesh creation techniques for models of discs of axial-flow microturbines. A universal method of optimization of such devices, in terms of their strength improvement, has been proposed. The research focused on microturbines that can operate in combination with ORC systems, especially the ones whose discs have many structural components such as pins or chamfers. Calculations were done using the commercial software ANSYS Workbench. Both tetrahedral and hexahedral grids were used in the analysed models. The calculation time needed for the grid preparation was regarded as an important parameter. Therefore, the reference model was created using the disc slice method. The results obtained for the models that included the full complex geometry of the disc were compared with the results obtained for the reference model. The mesh size coefficient was defined. It enabled to simplify the strength optimisation method for discs of axial-flow microturbine and also made it more universal. After carrying out all analyses and computations, it was possible to develop a scheme of conduct during the optimization of the aforementioned expansion devices.

Today, where the production of any kind of device may have a negative impact on the environment, it is crucial to produce machines that are as efficient as possible but that can also be strong enough to withstand harsh operating conditions for a long time. That is why this paper raises the issue of the fatigue analysis of high-speed axial-flow microturbines whose components are made of commonly used 7075 aluminium alloy. The paper presents different methods that can be used to estimate and increase the fatigue life of a turbine disc. The object of study is a 10-kilowatt vapour microturbine. The various mechanical, flow and thermal loads that can occur during the operation of the microturbine have been analysed so that the most important ones can be taken into account in the final considerations. Stress calculations were performed using analytical equations, and the finite element method (FEM) was also used. Using the stresses obtained and material characteristics, fatigue analysis was conducted. Then, new hybrid calculation methods were proposed, taking into account both analytical and numerical approaches that do not require the use of ready-made programs dedicated to fatigue analysis. To verify these methods, calculations were performed for two rotor discs with different geometries. These methods can be used by both engineers and scientists in the design process of various microturbines when fatigue calculations are performed.