The hypersonic boundary-layer receptivity to slow acoustic waves is investigated for the Mach 6 flow over a 5-degree half-angle blunt cone with the nose radius of 5.08 mm. The plane acoustic wave interacts with the bo...The hypersonic boundary-layer receptivity to slow acoustic waves is investigated for the Mach 6 flow over a 5-degree half-angle blunt cone with the nose radius of 5.08 mm. The plane acoustic wave interacts with the bow shock, and generates all types of disturbances behind the shock, which may take various routes to generate the boundarylayer unstable mode. In this paper, two routes of receptivity are investigated in detail.One is through the disturbance in the entropy layer. The other is through the slow acoustic wave transmitted downstream the bow shock, which can excite the boundary-layer mode due to the synchronization mechanism. The results show that, for a low frequency slow acoustic wave, the latter route plays a leading role. The entropy-layer instability wave is able to excite the first mode near the neutral point, but its receptivity efficiency is much lower.展开更多
Over the past decade,the cast aluminum alloys with excellent mechanical and conductivity properties have emerged as potential materials for thermal management.However,the traditional Al-Si based alloys are difficult t...Over the past decade,the cast aluminum alloys with excellent mechanical and conductivity properties have emerged as potential materials for thermal management.However,the traditional Al-Si based alloys are difficult to make significant breakthrough in conductivity performance.The hypoeutectic Al-5Ni alloy also possesses sound castability and is expected to be applied in thermal management applications.In this study,the effects of ytterbium(Yb element) at 0-0.5 wt% on the microstructures as well as the electrical/thermal conductivity and mechanical properties of the Al-5Ni alloy were systematically investigated.The experimental results indicate that the addition of Yb at a relatively low amount not only reduces the secondary dendrite arm spacing of the α-Al grains,but also modifies the morphology and distribution of eutectic boundary phase.Moreover,it is found that the dosage of Yb at 0.3 wt% in the Al-5Ni alloy can simultaneously improve the yield strength,ultimate tensile strength and electrical/thermal conductivity.The strengthening and toughening of the Al-5Ni alloy are mainly attributed to the decrease of secondary dendrite arm spacing and the improvement of eutectic phases.The transmission electron microscopy/selected area electron diffraction(TEM/SAED) analysis indicates that the ytterbium in Al-5Ni alloy will form Al_(3)Yb phase,which mainly agglomerates in the Al_(3)Ni phase region.This phase is helpful to decrease the solubility of impurity elements(e.g.,Fe and Si) in the α-Al matrix,which is beneficial to electrical/thermal conductivity.The value of this study lays foundation for manufacturing Al-Ni alloys with high thermal conductivity and acceptable mechanical properties.展开更多
Boundary layer transition(BLT)can cause a sharp rise in heat flux and skin friction,which can seriously affect the flight performance and safety of hypersonic flight vehicles.Therefore,the mechanism,prediction and con...Boundary layer transition(BLT)can cause a sharp rise in heat flux and skin friction,which can seriously affect the flight performance and safety of hypersonic flight vehicles.Therefore,the mechanism,prediction and control of transition have become important issues that must be dealt with for the development of advanced flight vehicles,and it is also a research hotspot of particular interest to major aerospace countries.Compared to other transition research approaches,model flight tests can better present the transition problems under real flight conditions,thus have been carried out extensively over the past 30 years.The United States,Germany,France,Australia,and other countries have carried out transition research based on flight tests,such as the Pegasus wing-glove crossflow transition and the Hypersonic Boundary Layer Transition(HyBOLT)transition control flight test of the United States,the joint research project of the Hypersonic International Flight Research and Experimentation-1(HIFiRE-1)circular cone and the HIFiRE-5 elliptic cone transition flight tests between the United States and Australia,the flight test of compression surface transition of the scramjet forebody(LEA)in France and so on.Although these flight tests suffered various setbacks,they still obtained valuable transition data.Recently,the United States is carrying out the concave-surface transition flight tests of Hypersonic Boundary Layer Transition(BOLT)and BOLT-II.Since its first model flight test mission for verification purpose launched successfully in 2015,several hypersonic BLT flight tests have been conducted by China Aerodynamics Research and Development Center(CARDC).The flight tests have measured valid transition data under flight conditions,obtained the transition front and its dynamical variation on blunt cones at various angles of attack and a lifting body Hypersonic Transition Research Vehicle(HyTRV).The crossflow traveling waves in high-altitude flight were measured for the first time,and our understanding of hypersonic BLT has been greatly improved.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.11472188 and11332007)the National Key Research and Development Program of China(No.2016YFA0401200)
文摘The hypersonic boundary-layer receptivity to slow acoustic waves is investigated for the Mach 6 flow over a 5-degree half-angle blunt cone with the nose radius of 5.08 mm. The plane acoustic wave interacts with the bow shock, and generates all types of disturbances behind the shock, which may take various routes to generate the boundarylayer unstable mode. In this paper, two routes of receptivity are investigated in detail.One is through the disturbance in the entropy layer. The other is through the slow acoustic wave transmitted downstream the bow shock, which can excite the boundary-layer mode due to the synchronization mechanism. The results show that, for a low frequency slow acoustic wave, the latter route plays a leading role. The entropy-layer instability wave is able to excite the first mode near the neutral point, but its receptivity efficiency is much lower.
基金supported by the National Natural Science Foundation of China(Grant Nos.12002353 and 92052301)the National Numerical Windtunnel Project,and the innovation foundation from the State Key Laboratory of Aerodynamics(Grant No.JBKYC190107)。
基金Project supported by the Guangdong Basic and Applied Basic Research Foundation (2019A1515110135,2021A1515010587)the Young Innovative Talents Projects of Universities in Guangdong Province(2020KQNCX084)the Guangdong Start-up Funds of DGUT (GC300502-52)。
文摘Over the past decade,the cast aluminum alloys with excellent mechanical and conductivity properties have emerged as potential materials for thermal management.However,the traditional Al-Si based alloys are difficult to make significant breakthrough in conductivity performance.The hypoeutectic Al-5Ni alloy also possesses sound castability and is expected to be applied in thermal management applications.In this study,the effects of ytterbium(Yb element) at 0-0.5 wt% on the microstructures as well as the electrical/thermal conductivity and mechanical properties of the Al-5Ni alloy were systematically investigated.The experimental results indicate that the addition of Yb at a relatively low amount not only reduces the secondary dendrite arm spacing of the α-Al grains,but also modifies the morphology and distribution of eutectic boundary phase.Moreover,it is found that the dosage of Yb at 0.3 wt% in the Al-5Ni alloy can simultaneously improve the yield strength,ultimate tensile strength and electrical/thermal conductivity.The strengthening and toughening of the Al-5Ni alloy are mainly attributed to the decrease of secondary dendrite arm spacing and the improvement of eutectic phases.The transmission electron microscopy/selected area electron diffraction(TEM/SAED) analysis indicates that the ytterbium in Al-5Ni alloy will form Al_(3)Yb phase,which mainly agglomerates in the Al_(3)Ni phase region.This phase is helpful to decrease the solubility of impurity elements(e.g.,Fe and Si) in the α-Al matrix,which is beneficial to electrical/thermal conductivity.The value of this study lays foundation for manufacturing Al-Ni alloys with high thermal conductivity and acceptable mechanical properties.
基金This work was supported by the National Natural Science Foundation of China(Grants 11772350,92052301).
文摘Boundary layer transition(BLT)can cause a sharp rise in heat flux and skin friction,which can seriously affect the flight performance and safety of hypersonic flight vehicles.Therefore,the mechanism,prediction and control of transition have become important issues that must be dealt with for the development of advanced flight vehicles,and it is also a research hotspot of particular interest to major aerospace countries.Compared to other transition research approaches,model flight tests can better present the transition problems under real flight conditions,thus have been carried out extensively over the past 30 years.The United States,Germany,France,Australia,and other countries have carried out transition research based on flight tests,such as the Pegasus wing-glove crossflow transition and the Hypersonic Boundary Layer Transition(HyBOLT)transition control flight test of the United States,the joint research project of the Hypersonic International Flight Research and Experimentation-1(HIFiRE-1)circular cone and the HIFiRE-5 elliptic cone transition flight tests between the United States and Australia,the flight test of compression surface transition of the scramjet forebody(LEA)in France and so on.Although these flight tests suffered various setbacks,they still obtained valuable transition data.Recently,the United States is carrying out the concave-surface transition flight tests of Hypersonic Boundary Layer Transition(BOLT)and BOLT-II.Since its first model flight test mission for verification purpose launched successfully in 2015,several hypersonic BLT flight tests have been conducted by China Aerodynamics Research and Development Center(CARDC).The flight tests have measured valid transition data under flight conditions,obtained the transition front and its dynamical variation on blunt cones at various angles of attack and a lifting body Hypersonic Transition Research Vehicle(HyTRV).The crossflow traveling waves in high-altitude flight were measured for the first time,and our understanding of hypersonic BLT has been greatly improved.
