Research On Characteristics Of Radial Turbine For Distributed Solar Thermal Power System Of Brayton Cycle

Distributed solar dish thermal power generation system operating in Brayton cycle has been paid more and more attention because of high concentration ratio,small capacity and being easy to combine with other kind of sources.Radial turbine,as the thermal power conversion component,is vital to the distributed solar dish thermal power generation system.It has the advantages of compact structure,high specific power,stable operation and wide adaptability to many working fluids.In this thesis,experiments and numerical simulations were conducted to study aerodynamic characteristics of a radial turbine and influence of different operating modes on the performance of the radial turbine.With compressed air being the working medium,a radial turbine test rig was constructed.Experiments were conducted to analyze the impact of temperature and pressure on the performance of the radial turbine.Experiment results show that the rotation speed and the output power of the radial turbine increase as the inlet temperature rises,while the expansion efficiency is little relative to the inlet temperature maintaining around 65%.When the inlet temperature keeps constant,the higher the inlet pressure is,the higher the output power and rotation speed of radial turbine are.Numerical simulation model was built after the geometry of impeller and volute of radial turbine were obtained by reversing engineering.Numerical simulations were implemented by using the experimental outlet pressure and temperature of an absorber as the boundary conditions.The discrepancy of mass flow rate between experiment result and numerical simulation is less than 7.7%,which validated the accuracy of numerical model.Analysis of flow field inside the volute reveals that the pressure and temperature are evenly distributed in the volute and good diversion is achieved while the flow near volute throat is complicated.The flow field distribution at different blade heights inside the rotor shows that energy loss caused by the low velocity separation zone at the leading and trailing edges of the blade,reduces the turbine efficiency.Based on a solar hybrid thermal power generation system complemented with thermal energy storage and fossil fuel,system control strategies concerning three operating modes(solar energy,solar energy combined with heat storage,solar energy combined with gas)are explored when solar radiation changes.Impact of different operating mode on radial turbine performance was studied by numerical simulation.Simulation results show that shaft power of radial turbine and rotation speed decrease 3% and 2% respectively when solar only mode or thermal energy storage discharging mode was switched to fossil fuel back up mode with the constant inlet temperature.This indicates that the operating mode change has little effect on the turbine performance in solar hybrid Brayton cycle system.With thermal energy storage or fossil fuel backing up,solar dish thermal power generation system can operate consistently and reliably.