Design and analysis of pioneering high supersonic axial turbines

The trend towards ultra compact thermal power generation, is constrained by the unavailability of fluid-machinery adequate for supersonic flow conditions. Conventional turbine designs exhibit unacceptable performances related to large aerodynamic losses and a narrow operation range. This paper provides for the first time in the open literature the design procedure, and subsequent analysis of the turbine performance of a turbine adequate for supersonic axial pulsating flows, as those encountered in innovative combustors. The design approach considers the most adverse condition, a steady inlet axial Mach number equal to 3.5. The possible turbine families were classified by the velocity triangles and discussed. A fundamental issue in supersonic passages is to ensure the normal shock at the start of the engine is swallowed through the turbine passages, namely the turbine passage is started. To ensure self-starting capability the turning is restricted to lower values than in the conventional subsonic turbines. The design procedure was based on the method of characteristics, converting the inlet uniform flow into a vortex flow field, such that the adequate deflection is inflicted to the supersonic flow. The performance of the supersonic passage was first assessed and then compared to conventional designs. The present design procedure and analysis of unconventional supersonic turbines provides guidelines for the design and optimization of efficient high supersonic passages, suitable to future tightly packed fluid machinery.