Today the Organic Rankine Cycle(ORC) is considered as one of the most promising technologies to recover the power from low-grade heat resources. In order to realize a high performance ORC turbine, the Computational Fl...Today the Organic Rankine Cycle(ORC) is considered as one of the most promising technologies to recover the power from low-grade heat resources. In order to realize a high performance ORC turbine, the Computational Fluid Dynamics(CFD) is extensively used to simulate the internal flow in the aerodynamic design. But due to the high non-ideality of the working fluid, it is crucial to take the real gas effect into consideration.In the present study, an accurate and reliable method of the perfect gas approximation for an organic working fluid(R245 fa) is developed. At first, the effectiveness of a perfect gas approximation is examined in two-dimensional CFD simulations of a convergent-divergent nozzle. Then the accuracy of the perfect gas approximation, definition of suitable nondimensional performance parameters and effective conversion method between the different gas models are studied in three-dimensional CFD simulations of an ORC radial-inflow turbine.展开更多
Bent inlet pipes are often used in centrifugal compressors due to limited installation space,and an understanding of the effect on compressor stability is essential for safety and durability.This paper firstly investi...Bent inlet pipes are often used in centrifugal compressors due to limited installation space,and an understanding of the effect on compressor stability is essential for safety and durability.This paper firstly investigates flow instability behaviors in two compressors,one with a straight inlet pipe and the other with an S-shaped bent pipe.In detail,it analyzes the resulting flow fields,instability evolution paths and surge boundaries.The results show that the S-shaped pipe obviously affects the flow field at high mass flow rates,while reverse flow mainly influences the flow field at low mass flow rates.Reverse flow first occurs at certain flow passages with a high pressure difference that is predominantly decided by the volute rather than the S-shaped bent pipe.In addition,centrifugal compressors can tolerate reverse flow to some extent so that surge would not occur immediately if reverse flow occurs unless the reverse flow region extends circumferentially and radially to a sufficiently large size.Since the S-shaped pipe is not dominant in the creation and extension of reverse flow,it does not exacerbate the stability of the central compressor to a great extent.Last but not least,the S-shaped pipe is noted to delay the occurrence of surge at 90%rotating speed,which suggests the possibility of improving compressor stability with bent inlet pipes.This result differs from the conventional understanding that inlet distortion usually deteriorates compressor stability and emphasizes the particularity of centrifugal compressors.展开更多
文摘Today the Organic Rankine Cycle(ORC) is considered as one of the most promising technologies to recover the power from low-grade heat resources. In order to realize a high performance ORC turbine, the Computational Fluid Dynamics(CFD) is extensively used to simulate the internal flow in the aerodynamic design. But due to the high non-ideality of the working fluid, it is crucial to take the real gas effect into consideration.In the present study, an accurate and reliable method of the perfect gas approximation for an organic working fluid(R245 fa) is developed. At first, the effectiveness of a perfect gas approximation is examined in two-dimensional CFD simulations of a convergent-divergent nozzle. Then the accuracy of the perfect gas approximation, definition of suitable nondimensional performance parameters and effective conversion method between the different gas models are studied in three-dimensional CFD simulations of an ORC radial-inflow turbine.
基金co-supported by the Tsinghua University"Shuimu Tsinghua Scholar"Programthe National Science and Technology Major Project+2 种基金China(No.2017-II-0004-0016)the National Natural Science Foundation of China(No.51876097)the IHI Corporation,Yokohama,Japan。
文摘Bent inlet pipes are often used in centrifugal compressors due to limited installation space,and an understanding of the effect on compressor stability is essential for safety and durability.This paper firstly investigates flow instability behaviors in two compressors,one with a straight inlet pipe and the other with an S-shaped bent pipe.In detail,it analyzes the resulting flow fields,instability evolution paths and surge boundaries.The results show that the S-shaped pipe obviously affects the flow field at high mass flow rates,while reverse flow mainly influences the flow field at low mass flow rates.Reverse flow first occurs at certain flow passages with a high pressure difference that is predominantly decided by the volute rather than the S-shaped bent pipe.In addition,centrifugal compressors can tolerate reverse flow to some extent so that surge would not occur immediately if reverse flow occurs unless the reverse flow region extends circumferentially and radially to a sufficiently large size.Since the S-shaped pipe is not dominant in the creation and extension of reverse flow,it does not exacerbate the stability of the central compressor to a great extent.Last but not least,the S-shaped pipe is noted to delay the occurrence of surge at 90%rotating speed,which suggests the possibility of improving compressor stability with bent inlet pipes.This result differs from the conventional understanding that inlet distortion usually deteriorates compressor stability and emphasizes the particularity of centrifugal compressors.
