Accurate aerodynamic heating prediction is of great significance to current manned space flight and deep space exploration missions.The temperature in the shock layer surrounding the reentry vehicle can reach up to 10...Accurate aerodynamic heating prediction is of great significance to current manned space flight and deep space exploration missions.The temperature in the shock layer surrounding the reentry vehicle can reach up to 10,000 K and result in remarkable thermochemical nonequilibrium,as well as considerable radiative heat transfer.In general,high-temperature flow simulations coupled with thermal radiation require appropriate numerical schemes and physical models.In this paper,the equations governing hypersonic nonequilibrium flow,based on a three-temperature model combined with a thermal radiation solving approach,are used to investigate the radiation effects in the reentry shock layer.An axisymmetric spherical case shows that coupling the flow-field simulation with radiation has a scarce influence on the convective heating prediction,but has some impact on the radiative heating calculation.In particular,for the Apollo capsule reentry,both the absorption coefficient and incident radiation are remarkable inside the shock layer.The radiative heating maximum reaches nearly 38%of that of the convective heating making a considerable contribution to the total aerodynamic heating.These results indicate that in the hypersonic regime,in order to account for the total heating,it is necessary to simulate the high-temperature thermochemical nonequilibrium flows coupled with thermal radiation.展开更多
For metal-intermetallic laminated composites,various types of defects often occur during the preparation process.This paper studied the evolution and formation mechanism of defects,such as pores,tunnel cracks,and dela...For metal-intermetallic laminated composites,various types of defects often occur during the preparation process.This paper studied the evolution and formation mechanism of defects,such as pores,tunnel cracks,and delamination cracks in Ti-Al_(3)Ti laminated composites prepared by vacuum hot-pressing method.Moreover,quasi-static and dynamic compression tests were performed to study the effects of pores and delamination cracks on the compression properties of the composites.The results showed that for Ti-Al_(3)Ti laminated composites prepared at 710℃,their Al_(3)Ti layers exhibit a porous structure,and the porosity of Al_(3)Ti layers firstly decreases and then increases under the combined action of press,the self-propagating reaction and Al3Ti grain coarsening.The tunnel cracks in Ti-Al_(3)Ti laminated composites are resulted by tensile residual stresses and the inherent brittleness of Al3Ti.For Ti-Al_(3)Ti laminated composites prepared at 680°C,the formation of delamination cracks is mainly related to the diffuse reaction of Ti/Al atoms and the Kirkendall effect,and the numbers of delamination cracks increase with the increasing of sintering time.Moreover,the pores and delamination cracks greatly deteriorate the compression properties of Ti-Al_(3)Ti laminated composites.Crack-free and dense Ti-Al_(3)Ti laminated composites exhibit the highest compression properties.展开更多
基金supported by the Shandong Provincial Natural Science Foundation,China(No.ZR2019QA018)the Advanced Research Project(No.61402060301).
文摘Accurate aerodynamic heating prediction is of great significance to current manned space flight and deep space exploration missions.The temperature in the shock layer surrounding the reentry vehicle can reach up to 10,000 K and result in remarkable thermochemical nonequilibrium,as well as considerable radiative heat transfer.In general,high-temperature flow simulations coupled with thermal radiation require appropriate numerical schemes and physical models.In this paper,the equations governing hypersonic nonequilibrium flow,based on a three-temperature model combined with a thermal radiation solving approach,are used to investigate the radiation effects in the reentry shock layer.An axisymmetric spherical case shows that coupling the flow-field simulation with radiation has a scarce influence on the convective heating prediction,but has some impact on the radiative heating calculation.In particular,for the Apollo capsule reentry,both the absorption coefficient and incident radiation are remarkable inside the shock layer.The radiative heating maximum reaches nearly 38%of that of the convective heating making a considerable contribution to the total aerodynamic heating.These results indicate that in the hypersonic regime,in order to account for the total heating,it is necessary to simulate the high-temperature thermochemical nonequilibrium flows coupled with thermal radiation.
基金co-supported by the National Natural Science Foundation of China(No.51201155)the Natural Science of Shanxi Province of China(No.2012011019-1)the Chinese Education Ministry Foundation for Doctors of China(No.20101420120006).
文摘For metal-intermetallic laminated composites,various types of defects often occur during the preparation process.This paper studied the evolution and formation mechanism of defects,such as pores,tunnel cracks,and delamination cracks in Ti-Al_(3)Ti laminated composites prepared by vacuum hot-pressing method.Moreover,quasi-static and dynamic compression tests were performed to study the effects of pores and delamination cracks on the compression properties of the composites.The results showed that for Ti-Al_(3)Ti laminated composites prepared at 710℃,their Al_(3)Ti layers exhibit a porous structure,and the porosity of Al_(3)Ti layers firstly decreases and then increases under the combined action of press,the self-propagating reaction and Al3Ti grain coarsening.The tunnel cracks in Ti-Al_(3)Ti laminated composites are resulted by tensile residual stresses and the inherent brittleness of Al3Ti.For Ti-Al_(3)Ti laminated composites prepared at 680°C,the formation of delamination cracks is mainly related to the diffuse reaction of Ti/Al atoms and the Kirkendall effect,and the numbers of delamination cracks increase with the increasing of sintering time.Moreover,the pores and delamination cracks greatly deteriorate the compression properties of Ti-Al_(3)Ti laminated composites.Crack-free and dense Ti-Al_(3)Ti laminated composites exhibit the highest compression properties.
