乘波体在高空高超声速飞行时,流场温度急剧升高,气体热力学性质发生改变,其气动特性与采用完全气体模型得到的结果存在差异,因此在飞行器设计中开展真实气体效应影响研究具有重要的工程价值。本文针对锥导乘波体设计提出了一种考虑平衡...乘波体在高空高超声速飞行时,流场温度急剧升高,气体热力学性质发生改变,其气动特性与采用完全气体模型得到的结果存在差异,因此在飞行器设计中开展真实气体效应影响研究具有重要的工程价值。本文针对锥导乘波体设计提出了一种考虑平衡气体效应的特征线方法(Method of characteristic, MOC),基于不同半锥角和不同流动捕获曲线生成了不同外形的乘波体,并使用快速估算方法估算平衡气体条件和完全气体条件下各乘波体的气动特性和几何特征参数,研究了不同气体模型对乘波体设计结果的影响。研究结果表明,高马赫数下基于平衡气体模型设计得到的乘波体升阻比、容积率和俯仰力矩系数等特性参数相比完全气体结果存在差异,并且平衡气体效应对不同外形乘波体的影响程度和影响规律不同。展开更多
The Rotation and Curvature(RC)correction is an important turbulence model modifi-cation approach,and the Spalart-Allmaras model with the RC correction(SA-RC)has been exten-sively studied and used.As a multiplier of th...The Rotation and Curvature(RC)correction is an important turbulence model modifi-cation approach,and the Spalart-Allmaras model with the RC correction(SA-RC)has been exten-sively studied and used.As a multiplier of the modelling equation’s production term,the rotation function f_(r1)should have a cautiously designed value range,but its limit varies in different models and flow solvers.Therefore,the need of restriction is discussed theoretically,and the common range of f_(r1)is explored in Burgers vortexes.Afterwards,the SA-RC model with different limits is tested numerically.Negative f_(r1)always appears in the SA-RC model,and the difference between simula-tion results brought by the limits is not negligible.A lower limit of 0 enhances turbulence produc-tion,and therefore the vortex structures are dissipated faster and shrink in size,while an upper limit plays an opposite role.Considering that the lower limit of 0 usually promotes the simulation accu-racy and fixes the numerical defect,whereas the upper limit worsens the predictive performance in most cases,it is recommended to limit f_(r1)non-negative while utilizing the SA-RC model.In addi-tion,the RC-corrected model has a better prediction of the attached flow near curved walls,while the SA-Helicity model largely improves the simulation accuracy of three-dimensional large-scale vortices.The model combining both corrections has the potential to become more adaptive and more accurate.展开更多
Chlorosis at leaf margins is a typical symptom of potassium(K) deficiency, but inappropriate application of K with other nutrients often masks symptoms of K deficiency. A two-year field experiment was conducted to mea...Chlorosis at leaf margins is a typical symptom of potassium(K) deficiency, but inappropriate application of K with other nutrients often masks symptoms of K deficiency. A two-year field experiment was conducted to measure the interactive effects of N and K on leaf photosynthesis and dry matter accumulation and the resulting growth dilution effect on K concentration and leaf K deficiency symptoms. N application aggravated the imbalance of N and K nutrients and further exacerbated K deficiency symptoms under K limitation. Synergistic effects of N and K promoted plant growth, amplified the growth dilution effect, and reduced the critical K concentration in leaves. Using 90% of the maximum shoot biomass as a threshold,the critical K concentration was 0.72% at the recommended N(N180) fertilization level. The critical K concentration increased by 62.5% owing to the reduced biomass under insufficient N(N;) supply. In contrast, high N(N;) reduced the critical K concentration(0.64%), accelerating chlorophyll decomposition and exacerbating K deficiency symptoms. The basis of changing the critical K concentration by magnifying growth dilution effect was the functional synergistic effect of N and K on photosynthetic characteristics. Under insufficient N, the low maximum carboxylation rate(V;) limited the net photosynthetic rate(An) and necessitated more K to maintain high CO;transmission capacity, to improve the total conductance g;/V;ratio. High N supply increased gtotand V;possibly mitigating the effect of K reduction on photosynthesis. In conclusion, it is unwise to judge K status of plants only by K concentration without accounting for crop mass(or dilution effect), critical K concentration and deficiency symptoms are affected by N fertilization, and the synergistic effect of N and K on leaf photosynthesis is the foundation of maximal growth of plants under diverse critical K concentrations.展开更多
Fast reactors based on thorium fuel have enhanced inherent safety. Fluoride salt performs well as a coolant in high-temperature nuclear systems. In this paper,we present a reference core for a large fluoride-salt-cool...Fast reactors based on thorium fuel have enhanced inherent safety. Fluoride salt performs well as a coolant in high-temperature nuclear systems. In this paper,we present a reference core for a large fluoride-salt-cooled solid-fuel fast reactor(LSFR) using thorium–uranium fuel cycle. Neutronics physics of the LSFR reference core is investigated with 2D and 3D in-core fuel management strategy. The design parameters analyzed include the fuel volume fraction, power density level and continuous removal of fission products with 3D fuel shuffling that obtains better equilibrium core performance than 2D shuffling. A self-sustained core is achieved for all cases,and the core of 60% fuel volume fraction at 50 MW/m^3 power density is of the best breeding performance(average breeding ratio 1.134). The LSFR core based on thorium fuel is advantageous in its high discharge burn-up of 20–30% fissions per initial heavy metal atom, small reactivity swing over the whole lifetime(to simplify the reactivity control system), the negative reactivity temperature coefficient(intrinsically safe for all cases) and accepted cladding peak radiation damage. The LSFR reactor is a good alternative option for the deployment of a self-sustained thorium-based nuclear system.展开更多
文摘乘波体在高空高超声速飞行时,流场温度急剧升高,气体热力学性质发生改变,其气动特性与采用完全气体模型得到的结果存在差异,因此在飞行器设计中开展真实气体效应影响研究具有重要的工程价值。本文针对锥导乘波体设计提出了一种考虑平衡气体效应的特征线方法(Method of characteristic, MOC),基于不同半锥角和不同流动捕获曲线生成了不同外形的乘波体,并使用快速估算方法估算平衡气体条件和完全气体条件下各乘波体的气动特性和几何特征参数,研究了不同气体模型对乘波体设计结果的影响。研究结果表明,高马赫数下基于平衡气体模型设计得到的乘波体升阻比、容积率和俯仰力矩系数等特性参数相比完全气体结果存在差异,并且平衡气体效应对不同外形乘波体的影响程度和影响规律不同。
基金supported by the National Natural Science Foundation of China(Nos.51976006,51790513)the Aeronautical Science Foundation of China(No.2018ZB51013)+1 种基金the National Science and Technology Major Project,China(2017-II-003-0015)the Open Fund from State Key Laboratory of Aerodynamics,China(No.SKLA2019A0101).
文摘The Rotation and Curvature(RC)correction is an important turbulence model modifi-cation approach,and the Spalart-Allmaras model with the RC correction(SA-RC)has been exten-sively studied and used.As a multiplier of the modelling equation’s production term,the rotation function f_(r1)should have a cautiously designed value range,but its limit varies in different models and flow solvers.Therefore,the need of restriction is discussed theoretically,and the common range of f_(r1)is explored in Burgers vortexes.Afterwards,the SA-RC model with different limits is tested numerically.Negative f_(r1)always appears in the SA-RC model,and the difference between simula-tion results brought by the limits is not negligible.A lower limit of 0 enhances turbulence produc-tion,and therefore the vortex structures are dissipated faster and shrink in size,while an upper limit plays an opposite role.Considering that the lower limit of 0 usually promotes the simulation accu-racy and fixes the numerical defect,whereas the upper limit worsens the predictive performance in most cases,it is recommended to limit f_(r1)non-negative while utilizing the SA-RC model.In addi-tion,the RC-corrected model has a better prediction of the attached flow near curved walls,while the SA-Helicity model largely improves the simulation accuracy of three-dimensional large-scale vortices.The model combining both corrections has the potential to become more adaptive and more accurate.
基金financially supported by the National Natural Science Foundation of China(31872173)the National Key Research and Development Program of China(2018YFD0200900)+1 种基金China Agriculture Research System(CARS-12)the Fundamental Research Funds for the Central Universities(2662018PY077)。
文摘Chlorosis at leaf margins is a typical symptom of potassium(K) deficiency, but inappropriate application of K with other nutrients often masks symptoms of K deficiency. A two-year field experiment was conducted to measure the interactive effects of N and K on leaf photosynthesis and dry matter accumulation and the resulting growth dilution effect on K concentration and leaf K deficiency symptoms. N application aggravated the imbalance of N and K nutrients and further exacerbated K deficiency symptoms under K limitation. Synergistic effects of N and K promoted plant growth, amplified the growth dilution effect, and reduced the critical K concentration in leaves. Using 90% of the maximum shoot biomass as a threshold,the critical K concentration was 0.72% at the recommended N(N180) fertilization level. The critical K concentration increased by 62.5% owing to the reduced biomass under insufficient N(N;) supply. In contrast, high N(N;) reduced the critical K concentration(0.64%), accelerating chlorophyll decomposition and exacerbating K deficiency symptoms. The basis of changing the critical K concentration by magnifying growth dilution effect was the functional synergistic effect of N and K on photosynthetic characteristics. Under insufficient N, the low maximum carboxylation rate(V;) limited the net photosynthetic rate(An) and necessitated more K to maintain high CO;transmission capacity, to improve the total conductance g;/V;ratio. High N supply increased gtotand V;possibly mitigating the effect of K reduction on photosynthesis. In conclusion, it is unwise to judge K status of plants only by K concentration without accounting for crop mass(or dilution effect), critical K concentration and deficiency symptoms are affected by N fertilization, and the synergistic effect of N and K on leaf photosynthesis is the foundation of maximal growth of plants under diverse critical K concentrations.
基金supported by the ‘‘Strategic Priority Research Program’’ of the Chinese Academy of Sciences(No.XDA02010200)the Frontier Science Key Program of Chinese Academy of Sciences(No.QYZDY-SSW-JSC016)
文摘Fast reactors based on thorium fuel have enhanced inherent safety. Fluoride salt performs well as a coolant in high-temperature nuclear systems. In this paper,we present a reference core for a large fluoride-salt-cooled solid-fuel fast reactor(LSFR) using thorium–uranium fuel cycle. Neutronics physics of the LSFR reference core is investigated with 2D and 3D in-core fuel management strategy. The design parameters analyzed include the fuel volume fraction, power density level and continuous removal of fission products with 3D fuel shuffling that obtains better equilibrium core performance than 2D shuffling. A self-sustained core is achieved for all cases,and the core of 60% fuel volume fraction at 50 MW/m^3 power density is of the best breeding performance(average breeding ratio 1.134). The LSFR core based on thorium fuel is advantageous in its high discharge burn-up of 20–30% fissions per initial heavy metal atom, small reactivity swing over the whole lifetime(to simplify the reactivity control system), the negative reactivity temperature coefficient(intrinsically safe for all cases) and accepted cladding peak radiation damage. The LSFR reactor is a good alternative option for the deployment of a self-sustained thorium-based nuclear system.
