Miniature gas turbines : numerical study of the effects of miniaturization on the performance of compressor

Abstract

Micro Gas Turbines (MGT) are an attractive choice for Unmanned Aerial Vehicles (UAV) and small-scale power generation. Compared with other propulsion systems, MGT have several advantages including high power-toweight ratio, availability for various fuels, endurance and others. However, the direct miniaturization of conventional gas turbines designed at large scales may induce performance loss. Therefore, the effects of miniaturization on gas turbines need to be investigated. In this research, an axial compressor in a gas turbine is studied, to understand the effects of the miniaturizing process. Using a numerical approach, parameter studies are conducted on three of the most important parameters during the miniaturizing process: the Reynolds number effect, the increased heat transfer and the tip clearance. The NASA Stage35 compressor is selected as the configuration in this study. Firstly, a thorough validation of the computational tools and methods is conducted, suggesting the suitability of the numerical methods for follow-up study. Then, the effect of Reynolds number is investigated, in the range of Re 2.14×10 5 to Re 8.54×10 5. Our results indicate a drop of performance with the decrease of Reynolds number, due to the increased viscous effect in boundary layer when compressor is miniaturized. Thereafter, the effect of heat transfer is investigated due to thermal conduction; adiabatic wall conditions, constant heat transfer coefficient conditions and isothermal conditions are applied, respectively. The results indicate that the increased heat transfer from internal flow to the ambient air will actually benefit compressor performance, but the heat transfer from the downstream combustor to the compressor has an adverse effect on compressor overall performance. Subsequently, the effect of tip clearance (TC) is investigated, with varying TC value and varying Reynolds number. Our results indicate that the existence of TC has an adverse effect on compressor performance, and the loss of performance amplifies during the miniaturization process.