Continuous drive friction welding was employed to join the aeronautic aluminum alloy 2024.Parametric optimization and microstructural characterization were investigated.Results show that friction pressure is the most ...Continuous drive friction welding was employed to join the aeronautic aluminum alloy 2024.Parametric optimization and microstructural characterization were investigated.Results show that friction pressure is the most significant factor influencing the tensile strength of joints.To obtain a high joint efficiency,the combination of moderate friction pressure,less friction time and higher upset pressure is recommended.The optimized joint efficiency from Taguchi analysis reaches 92% of base metal.Under the optimized experimental condition,the interfacial peak temperature is calculated analytically in the range of 779-794 K,which is validated by experimental data.Fine recrystallized grains caused by the high temperature and plastic deformation are observed in the friction interface zone.The grain refinement is limited in the thermo-mechanically affected zone,where most of matrix grains are deformed severely.The extensive dissolution and limited re-precipitation of strengthening phases result in a lower microhardness in the friction interface zone than that in the thermo-mechanically affected zone.展开更多
In this paper,a correlation model between centrifugal compressor and its piping system is built based on plenum chamber model and throttle valve model.This model could be used to conduct numerical analysis of compress...In this paper,a correlation model between centrifugal compressor and its piping system is built based on plenum chamber model and throttle valve model.This model could be used to conduct numerical analysis of compressor systems from steady to surge operating points.Three dimensional unsteady numerical simulations were performed to predict the performance of a centrifugal compressor.The flow structures in blade passage and diffuser were plotted and analyzed.The fluctuations of pressure and mass flow rate over time at the outlet of diffuser are obtained at surge condition.The characteristic changes of compressor-pipe network under the surge condition were carried out,and the effects of model characteristics including valve coefficient and backpressure on surge were analyzed.展开更多
Enhancing stall margin has a great importance for the development of turbo compressors. The application of circumferential grooved casing treatment(CGCT) is a useful method of increasing the stable operating range of ...Enhancing stall margin has a great importance for the development of turbo compressors. The application of circumferential grooved casing treatment(CGCT) is a useful method of increasing the stable operating range of the compressor, and the effectiveness of this kind of casing treatment have been proved by numerous experiments. In this paper, a single circumferential casing groove is placed along the shroud side of the vaned diffuser. To clarify the effect of circumferential groove on the centrifugal compressor stability and corresponding flow mechanism, numerical investigations with different radial location, axial depth and radial width were carried out to compare the results. The computational fluid dynamics(CFD) analyses results show that the centrifugal compressor with a single circumferential groove in diffuser passage can extend stable operating range while the efficiency over the whole operating range decreases a little. Efforts were made to study blade level flow mechanisms to determine how the circumferential groove impacts the compressor's stall margin(SM) and performance. Some comparisons of the flow features with different parameter of grooved casing treatment are performed, and the results indicate that the low energy flow in the tip clearance is sucked into the groove and the area of the low energy fluid region shrinks, which helps to improve the stall margin of the centrifugal compressor. The numerical results showed that a combination of position,width and depth of circumferential groove will maximize stall margin improvement(SMI) of the centrifugal compressor.展开更多
基金Project(51475196) supported by the National Natural Science Foundation of ChinaProject(2017ZX04004001) supported by the National Science and Technology Major Project on High-end Numerically Controlled Machine Tools and Basic Manufacturing Technology,China
文摘Continuous drive friction welding was employed to join the aeronautic aluminum alloy 2024.Parametric optimization and microstructural characterization were investigated.Results show that friction pressure is the most significant factor influencing the tensile strength of joints.To obtain a high joint efficiency,the combination of moderate friction pressure,less friction time and higher upset pressure is recommended.The optimized joint efficiency from Taguchi analysis reaches 92% of base metal.Under the optimized experimental condition,the interfacial peak temperature is calculated analytically in the range of 779-794 K,which is validated by experimental data.Fine recrystallized grains caused by the high temperature and plastic deformation are observed in the friction interface zone.The grain refinement is limited in the thermo-mechanically affected zone,where most of matrix grains are deformed severely.The extensive dissolution and limited re-precipitation of strengthening phases result in a lower microhardness in the friction interface zone than that in the thermo-mechanically affected zone.
基金The National Key Basic Research Program of China(No.2012CB026000)the National Natural Science Foundation of China(No.51776155)
文摘In this paper,a correlation model between centrifugal compressor and its piping system is built based on plenum chamber model and throttle valve model.This model could be used to conduct numerical analysis of compressor systems from steady to surge operating points.Three dimensional unsteady numerical simulations were performed to predict the performance of a centrifugal compressor.The flow structures in blade passage and diffuser were plotted and analyzed.The fluctuations of pressure and mass flow rate over time at the outlet of diffuser are obtained at surge condition.The characteristic changes of compressor-pipe network under the surge condition were carried out,and the effects of model characteristics including valve coefficient and backpressure on surge were analyzed.
基金National Natural Science Foundation of China(No.51776155)
文摘Enhancing stall margin has a great importance for the development of turbo compressors. The application of circumferential grooved casing treatment(CGCT) is a useful method of increasing the stable operating range of the compressor, and the effectiveness of this kind of casing treatment have been proved by numerous experiments. In this paper, a single circumferential casing groove is placed along the shroud side of the vaned diffuser. To clarify the effect of circumferential groove on the centrifugal compressor stability and corresponding flow mechanism, numerical investigations with different radial location, axial depth and radial width were carried out to compare the results. The computational fluid dynamics(CFD) analyses results show that the centrifugal compressor with a single circumferential groove in diffuser passage can extend stable operating range while the efficiency over the whole operating range decreases a little. Efforts were made to study blade level flow mechanisms to determine how the circumferential groove impacts the compressor's stall margin(SM) and performance. Some comparisons of the flow features with different parameter of grooved casing treatment are performed, and the results indicate that the low energy flow in the tip clearance is sucked into the groove and the area of the low energy fluid region shrinks, which helps to improve the stall margin of the centrifugal compressor. The numerical results showed that a combination of position,width and depth of circumferential groove will maximize stall margin improvement(SMI) of the centrifugal compressor.
