A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re = 3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow struc...A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re = 3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow structures were presented and compared with those for a circular cylinder at the same Reynolds number. The mean drag coefficient for the wavy cylinder is smaller than that for a corresponding circular cylinder due to the formation of a longer wake vortex generated by the wavy cylinder. The fluctuating lift coefficient of the wavy cylinder is also greatly reduced. This kind of wavy surface leads to the formation of 3-D free shear layers which are more stable than purely 2-D free shear layers. Such free shear layers only roll up into mature vortices at further downstream position and significantly modify the near wake structures and the pressure distributions around the wavy cylinder. Moreover, the simulations in laminar flow condition were also performed to investigate the effect of Reynolds number on force reduction control.展开更多
It is well known that riblet applied on compressor blades is a promising flow control technique. However, detailed investigation of its effects on the flow field of turbomachinery is rare in existing literatures. This...It is well known that riblet applied on compressor blades is a promising flow control technique. However, detailed investigation of its effects on the flow field of turbomachinery is rare in existing literatures. This paper presents a detailed experimental investigation of effects of distributed riblet on the flow field of an axial compressor iso- lated-rotor stage. The research was performed in a large-scale facility respectively with two configurations, in- eluding grooved hub, and grooved surface on both hub and partial suction surface. The riblet film is rectangle grooved type with a height of 0.1 ram. The flow field at 10% chord downstream from the cascade trailing edge was measured using a mini five-hole pressure probe and a total pressure probe. The testing was conducted at sev- eral operational points under two reduced rotational speeds. Stagnation pressure loss in rotational frame was cal- culated and compared with the control test in which a smooth film was applied to the corresponding position. Results show that with the grooved hub configuration at the design operation point of the lower rotational speed, the riblet film provides an obvious improvement of a 48% reduction of total pressure loss in rotational frame. Also, a distinct weaken hub comer vortex was identified. In the meantime, there exists a deviation of flow angle about 5 degrees at 20%-80% span which previously was not considered to be the affected region.展开更多
The anaerobic digestion(AD)disposal of stover and cattle manure is of great significance to the development of low-carbon economy and green energy in China,but it will also have an impact on the environment,and the de...The anaerobic digestion(AD)disposal of stover and cattle manure is of great significance to the development of low-carbon economy and green energy in China,but it will also have an impact on the environment,and the degree of influence is different for various raw materials.In this study,life cycle assessment(LCA)methods were applied to analyze and compare the impact of corn stovers biogas projects(CSBP)and dairy manure biogas projects(DMBP)on the environment during the whole operation stage.The results of inventory analysis were evaluated by ReCiPe2016 Hierarchy(H)mid-point(problem-oriented)and end-point(destruction-oriented)method,respectively.The results showed that the net energy efficiency of CSBP was higher(763.903 kW·h/FU)and the greenhouse gas(GHG)emission reduction of DMBP was more(5541.418 kg CO_(2)-eq/FU).The anaerobic digestion(AD)units have the greatest environmental impacts,and human carcinogenic toxicity is the largest environmental impact category(1.16-1.43 PE).The key to reducing environmental impact is reducing the input of chemical substances and the waste of electric energy.Both CSBP and DMBP have a favorable impact on ecosystem quality and resources,and CSBP is more beneficial to the environment(-10.297 Pt).Co-digestion is an important measure to reduce the environmental damage from biogas projects.These research results provide theoretical support for the selection of raw materials for large-scale biogas projects in China,provide technical basis for reducing the impact of actual operation on the environment,and promote the resource utilization of agricultural waste and carbon dioxide emission reduction and sequestration.展开更多
The effect of large thickness-reduction on microstructure evolution and tensile properties of Mg-9 Al-1 Zn alloy(AZ91)processed by hard-plate rolling(HPR)was investigated.Increasing rolling reduction from55%to 85%incr...The effect of large thickness-reduction on microstructure evolution and tensile properties of Mg-9 Al-1 Zn alloy(AZ91)processed by hard-plate rolling(HPR)was investigated.Increasing rolling reduction from55%to 85%increases the volume fraction and refines average size of fine grains(<3μm,FGs),leading to an optimized bimodal-grained structure consisting of coarse grains(CGs)uniformly embedded in FG regions.The sample with 85%reduction exhibits the highest yield strength of~314 MPa,ultimate tensile strength of~381 MPa and elongation of~11%.The high strength is primarily due to the contribution of grain boundaries(GBs)strengthening by FGs(accounting for~65%of strength),meanwhile the improved ductility originates from the optimized bimodal-grained structure and weakened basal texture that favor a higher ductility.The present findings successfully overcome the trade-off dilemma that the largereduction rolling processing on Mg alloys usually enhances strength at expense of ductility.In addition,the intensified heterogeneous deformation and favorable formation of a bimodal-grained microstructure during large-reduct ion HPR was addressed by tracing micro structure evolution details in grains of intere st via quasi-in-situ electron back scattering diffraction(EBSD).The present study can be instructive for further designing novel Mg alloys by tailoring bimodal-grained structures for superior combination of mechanical properties.展开更多
The keen interest in fuel cells and metal-air batteries stimulates a great deal of research on the development of a cost-efficient and high-performance catalyst as an alternative to traditional Pt to boost the sluggis...The keen interest in fuel cells and metal-air batteries stimulates a great deal of research on the development of a cost-efficient and high-performance catalyst as an alternative to traditional Pt to boost the sluggish oxygen reduction reaction(ORR)at the cathode.Herein,we report a facile and scalable strategy for the large-scale preparation of a free-standing and flexible porous atomically dispersed Fe-N-doped carbon microtube(FeSAC/PCMT)sponge.Benefiting from its unique structure that greatly facilitates the catalytic kinetics,mass transport,and electron transfer,our FeSAC/PCMT electrode exhibits excellent performance with an ORR potential of 0.942 V at^(-3) mA cm^(-2).When the FeSAC/PCMT sponge was directly used as an oxygen electrode for liquid-state and flexible solid-state zinc-air batteries,high peak power densities of 183.1 and 58.0 mW cm^(-2) were respectively achieved,better than its powdery counterpart and commercial Pt/C catalyst.Experimental and theoretical investigation results demonstrate that such ultrahigh ORR performance can be attributed to atomically dispersed Fe-N_(5) species in FeSAC/PCMT.This study presents a cost-effective and scalable strategy for the fabrication of highly efficient and flexible oxygen electrodes,provides a significant new insight into the catalytic mechanisms,and helps to realize significant advances in energy devices.展开更多
The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The...The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The austenite grains were refined after the reduction pretreatment experiment,especially those at the center of the billet.The effects of strain and strain rate on the average grain size were dependent on the deformation temperature.At a strain rate of 0.01 s-1 and 1200°C,the newly formed strain-free austenite grains grew very fast as the strain continued to increase,which resulted in the coarsening of austenite grains.The calculation results of the microstructure evolution model showed that at the same deformation temperature,the evolution curves of average grain size with different strain rates had the intersection points.With the increase in temperature,the position of intersection point moved to the downward direction of strain.The simulation results showed that when the reduction amount increased to 20%,the average grain size at the center was smaller than that near the surface.It could be inferred that when the reduction amount greatly exceeded 20%,the dynamic recrystallization at the center was mostly completed,and the austenite grain growth would become the main mechanism.展开更多
基金supported by the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 200804971025)the Council of the Hong Kong Special Administrative Region, China (Grant No. PolyU 5311/04E)
文摘A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re = 3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow structures were presented and compared with those for a circular cylinder at the same Reynolds number. The mean drag coefficient for the wavy cylinder is smaller than that for a corresponding circular cylinder due to the formation of a longer wake vortex generated by the wavy cylinder. The fluctuating lift coefficient of the wavy cylinder is also greatly reduced. This kind of wavy surface leads to the formation of 3-D free shear layers which are more stable than purely 2-D free shear layers. Such free shear layers only roll up into mature vortices at further downstream position and significantly modify the near wake structures and the pressure distributions around the wavy cylinder. Moreover, the simulations in laminar flow condition were also performed to investigate the effect of Reynolds number on force reduction control.
基金funded by the National Natural Science Foundation of China,Grant No.51161130525 and 51136003supported by the 111 Project,No.B07009
文摘It is well known that riblet applied on compressor blades is a promising flow control technique. However, detailed investigation of its effects on the flow field of turbomachinery is rare in existing literatures. This paper presents a detailed experimental investigation of effects of distributed riblet on the flow field of an axial compressor iso- lated-rotor stage. The research was performed in a large-scale facility respectively with two configurations, in- eluding grooved hub, and grooved surface on both hub and partial suction surface. The riblet film is rectangle grooved type with a height of 0.1 ram. The flow field at 10% chord downstream from the cascade trailing edge was measured using a mini five-hole pressure probe and a total pressure probe. The testing was conducted at sev- eral operational points under two reduced rotational speeds. Stagnation pressure loss in rotational frame was cal- culated and compared with the control test in which a smooth film was applied to the corresponding position. Results show that with the grooved hub configuration at the design operation point of the lower rotational speed, the riblet film provides an obvious improvement of a 48% reduction of total pressure loss in rotational frame. Also, a distinct weaken hub comer vortex was identified. In the meantime, there exists a deviation of flow angle about 5 degrees at 20%-80% span which previously was not considered to be the affected region.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFE0106000)the National Natural Science Foundation of China(Grant No.52206234).
文摘The anaerobic digestion(AD)disposal of stover and cattle manure is of great significance to the development of low-carbon economy and green energy in China,but it will also have an impact on the environment,and the degree of influence is different for various raw materials.In this study,life cycle assessment(LCA)methods were applied to analyze and compare the impact of corn stovers biogas projects(CSBP)and dairy manure biogas projects(DMBP)on the environment during the whole operation stage.The results of inventory analysis were evaluated by ReCiPe2016 Hierarchy(H)mid-point(problem-oriented)and end-point(destruction-oriented)method,respectively.The results showed that the net energy efficiency of CSBP was higher(763.903 kW·h/FU)and the greenhouse gas(GHG)emission reduction of DMBP was more(5541.418 kg CO_(2)-eq/FU).The anaerobic digestion(AD)units have the greatest environmental impacts,and human carcinogenic toxicity is the largest environmental impact category(1.16-1.43 PE).The key to reducing environmental impact is reducing the input of chemical substances and the waste of electric energy.Both CSBP and DMBP have a favorable impact on ecosystem quality and resources,and CSBP is more beneficial to the environment(-10.297 Pt).Co-digestion is an important measure to reduce the environmental damage from biogas projects.These research results provide theoretical support for the selection of raw materials for large-scale biogas projects in China,provide technical basis for reducing the impact of actual operation on the environment,and promote the resource utilization of agricultural waste and carbon dioxide emission reduction and sequestration.
基金supported by the Natural Science Foundation of China(Nos.51922048,51625402,51871108 and 51671093)Partial financial support came from the Changjiang Scholars Program(No.T2017035)。
文摘The effect of large thickness-reduction on microstructure evolution and tensile properties of Mg-9 Al-1 Zn alloy(AZ91)processed by hard-plate rolling(HPR)was investigated.Increasing rolling reduction from55%to 85%increases the volume fraction and refines average size of fine grains(<3μm,FGs),leading to an optimized bimodal-grained structure consisting of coarse grains(CGs)uniformly embedded in FG regions.The sample with 85%reduction exhibits the highest yield strength of~314 MPa,ultimate tensile strength of~381 MPa and elongation of~11%.The high strength is primarily due to the contribution of grain boundaries(GBs)strengthening by FGs(accounting for~65%of strength),meanwhile the improved ductility originates from the optimized bimodal-grained structure and weakened basal texture that favor a higher ductility.The present findings successfully overcome the trade-off dilemma that the largereduction rolling processing on Mg alloys usually enhances strength at expense of ductility.In addition,the intensified heterogeneous deformation and favorable formation of a bimodal-grained microstructure during large-reduct ion HPR was addressed by tracing micro structure evolution details in grains of intere st via quasi-in-situ electron back scattering diffraction(EBSD).The present study can be instructive for further designing novel Mg alloys by tailoring bimodal-grained structures for superior combination of mechanical properties.
基金supported by the start-up fund from Kunming University of Science and Technology,the National Natural Science Foundation of China (Grants 52102046,51872293,52130209,52072375)Liaoning Revitalization Talents Program (XLYC2002037)Basic Research Project of Natural Science Foundation of Shandong Province,China (ZR2019ZD49).
文摘The keen interest in fuel cells and metal-air batteries stimulates a great deal of research on the development of a cost-efficient and high-performance catalyst as an alternative to traditional Pt to boost the sluggish oxygen reduction reaction(ORR)at the cathode.Herein,we report a facile and scalable strategy for the large-scale preparation of a free-standing and flexible porous atomically dispersed Fe-N-doped carbon microtube(FeSAC/PCMT)sponge.Benefiting from its unique structure that greatly facilitates the catalytic kinetics,mass transport,and electron transfer,our FeSAC/PCMT electrode exhibits excellent performance with an ORR potential of 0.942 V at^(-3) mA cm^(-2).When the FeSAC/PCMT sponge was directly used as an oxygen electrode for liquid-state and flexible solid-state zinc-air batteries,high peak power densities of 183.1 and 58.0 mW cm^(-2) were respectively achieved,better than its powdery counterpart and commercial Pt/C catalyst.Experimental and theoretical investigation results demonstrate that such ultrahigh ORR performance can be attributed to atomically dispersed Fe-N_(5) species in FeSAC/PCMT.This study presents a cost-effective and scalable strategy for the fabrication of highly efficient and flexible oxygen electrodes,provides a significant new insight into the catalytic mechanisms,and helps to realize significant advances in energy devices.
基金funded by the National Key Research and Development Program of China(2021YFE0113200)the Fundamental Research Funds for the Central Universities(FRF-TP-20-104A1).
文摘The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The austenite grains were refined after the reduction pretreatment experiment,especially those at the center of the billet.The effects of strain and strain rate on the average grain size were dependent on the deformation temperature.At a strain rate of 0.01 s-1 and 1200°C,the newly formed strain-free austenite grains grew very fast as the strain continued to increase,which resulted in the coarsening of austenite grains.The calculation results of the microstructure evolution model showed that at the same deformation temperature,the evolution curves of average grain size with different strain rates had the intersection points.With the increase in temperature,the position of intersection point moved to the downward direction of strain.The simulation results showed that when the reduction amount increased to 20%,the average grain size at the center was smaller than that near the surface.It could be inferred that when the reduction amount greatly exceeded 20%,the dynamic recrystallization at the center was mostly completed,and the austenite grain growth would become the main mechanism.