Optimization Design And Flow Field Analysis Of R245fa Axial Flow Expander

In recent years,with the rapid development of society,the demand for energy has been increasing,but the reserves of non-renewable energy sources have been declining,such as coal and petroleum.So developing of sustainable new energy and making good use of lowtemperature industrial waste heat have received increasing attention.The organic Rankine cycle system(ORC)can effectively recover the low-grade heat energy.One of the key components in the ORC system is the turboexpander.In order to further improve the system efficiency,the design of high-performance turboexpander has become the goal pursued by many scholars.Based on this,the aerodynamic optimization design of ORC axial turboexpander using R245 fa working fluid power of 5MW is carried out in this paper.Like other turbomachinery designs,the design of an axial expander is a process of continuous modification and improvement from low to high dimensions.Based on the selfdeveloped one-dimensional aerodynamic design program,an AMDCKO model capable of predicting various losses has been added in this paper.At the same time,it integrates the real physical property module,which can realize the one-dimensional aerodynamic design of the real working fluid axial flow expander.In order to make the one-dimensional aerodynamic design of the axial expander easier and more efficient,this paper combines the one-dimensional aerodynamic design program with the global optimization algorithm,which can reduce dependence on design experience and shorten the design cycle.The stage pressure ratio,reaction and exit angle are selected as optimization variables.The isentropic efficiency is used as the optimization goal.The meridian channel dilation angle,the hub and shroud reaction of blade are constrained.Combined with the optimization algorithm,the one-dimensional optimization design of the ORC axial flow expander is realized.Efficient blade development is the guarantee for designing high-performance expanders.According to the one-dimensional design results,using the two-dimensional blade parameterization program,combined with the MISES solver and optimization method,the twodimensional blade optimal design of the axial flow expander is realized.Finally,the optimized design of the flow section of the 2-stage R245 fa axial flow expander is completed.The 2-stage axial flow expander scheme will cause high-intensity shock waves in the flow field.However,the optimized design of the two-dimensional blade can weaken the shock intensity of the supersonic blade,which can reduce the shock loss and improve the blade performance.In order to verify whether the design meets the design requirements,the NUMECA software is used to simulate and verify the three-dimensional constant value of the design scheme.The results show that the mass at the design point meets the requirements.The isentropic total-static efficiency is 91.13%,exceeding the design requirements by 6.13%.The output power also meets the requirements.At the same time,it shows better performance in all working conditions.The feasibility of the optimized design system of ORC axial turboexpander is verified.Finally,the value of the axial clearance of R245 fa axial flow expander designed is studied.Between the first-stage stator and rotor,the steady and unsteady numerical simulation of 5 different axial clearance are performed.The effects of the axial clearance on the expander blade wake,shock intensity and flow field are analyzed.The research results show that there is an optimal axial clearance between the first stage stator and rotor,which increases the isentropic total-static efficiency and isentropic total-total efficiency of the R245 fa axial flow expander by 0.2%.The reduction of the first stage stator wake loss and the reduction of shock intensity in the flow field lead to an increase in unit performance.The results of this paper provide technical support for the aerodynamic optimization design of high-performance axial flow expander.