Investigation Of Heat Transfer Effect In Small Gas Turbine

The small gas turbine is being used more widely accompany with its scale getting smaller and smaller, so the heat effect of gas turbine is more and more obvious nowadays. If we treat the gas flow as an adiabatic procedure, some mistakes of gas turbine design will be made. Because of the heat transfer from the hot side (mainly turbine) to the cold side (mainly compressor), many side-effects appear, such as the performance of compressor, turbine and the whole engine will be affected. The main work of this article is to investigate the inside heat transfer effect on the performance of non-adiabatic "back to back" small gas turbine. The thermodynamic model is analyzed to describe the mechanism of the heat transfer, and a non-rotating experiment rig is built to validate the heat transfer phenomenon by CFD or experiment. Further more the heat insulation method will be researched, and the design of non-adiabatic small gas turbine will be improved.First, on the work before, this article builds a non-adiabatic thermodynamic model of compressor and turbine. Based on certain assumptions, three different definitions of efficiency were proposed, that is adiabatic efficiency, diabatic efficiency and heat efficiency. It is found that the measurement efficiency (i.e. diabatic efficiency) can not describe the components' actual aerodynamic power, and it estimates the aerodynamic efficiency in error. Meanwhile the heat efficiency can be treated as actual aerodynamic efficiency. This article discusses the factors affect the efficiency and their relationship.The ANSYS CFX software is used in this article to investigate the fluid-thermal coupling CFD method of Markâ…¡test case and compare with experimental data. The research shows that even though the precision of fluid-thermal coupling numerical simulation is restricted by turbulence model, transition model and mesh density, its result is closer to real value compare to non-couple numerical simulation, and it meets the engineering demands. So the fluid-thermal coupling CFD method will promote the design of non-adiabatic small gas turbine greatly.Based on real "back to back" small gas turbine, using similarity criterion, a non-rotating model experiment rig, together with hardware and software test system, is built. Heat transfer experiment is carried out on this test rig, and the temperature distribution on compressor and turbine wall in different conditions is measured. The experiment data conform to CFD result very well, which proved the validity of fluid-thermal coupling CFD method. On the other hand, the effect of different heat insulation method are investigated, and it is found that reducing the radiation intensity of interspace is a effective way in engineering, which will provide the experience for real gas turbine.This article practices the CFD numerical simulation of an 80kW "back to back" non-adiabatic small gas turbine 3D model. Comparing the results, the difference of adiabatic simulation and coupling simulation is mainly reflected on temperature field, rather than pressure field or other field. Meanwhile, it is different in the situation that with or without heat insulation. It can be seen from the simulation result that with heat insulation the heat effect of gas turbine is obviously weaker, and this proves the validity of heat insulation design for non-adiabatic small gas turbine.Finally, for making the compressor match the turbine well, the design target of non-adiabatic small gas turbine is changed, and new aerodynamic design is tried. The new design compressor improves the through-flow capability, and reduces the size of diffuser. The simulation result shows that the heat effect of new design compressor is braked, which makes progress.