Flow velocity is a major parameter related to hillslope hydrodynamics erosion.This study aims to measure flow velocity over frozen and non-frozen slopes through leading edge method before being calibrated with accurat...Flow velocity is a major parameter related to hillslope hydrodynamics erosion.This study aims to measure flow velocity over frozen and non-frozen slopes through leading edge method before being calibrated with accurate flow velocity to determine the correct coefficient for convenience of flow velocity measurement.Laboratory experiments were conducted on frozen and non-frozen soil slopes with flumes involving four slope gradients of 5°,10°,15°,and 20°and three flow rates of 1,2,and 4 L/min with a flume of 6 m long and 0.1 m wide.The measurements were made with a stopwatch to record the time duration that the water flow ran over the rill segments of 2,4 and 6 m long.Accurate flow velocity was measured with electrolyte trace method,under pulse boundary condition.The leading edge and accurate flow velocities were used to determine the correction coefficient to convert the former to the latter.Results showed that the correction coefficient on frozen soil slope was 0.81 with a coefficient of determination(R2)of 0.99.The correction coefficient on non-frozen soil slope was 0.79 with R2 of 0.98.A coefficient of 0.8 was applicable to both soil surface conditions.The accurate velocities on the four frozen black soil slopes were approximately 30%,54%,71%,and 91%higher than those on non-frozen soil slopes.By contrast,the leading edge flow velocities on the frozen soil slopes were 23%,54%,67%,and 84%higher than those on non-frozen soil slopes.The flow velocities on frozen soil slopes increased with flow rate at all four slopes,but they increased from 5 to 15°before getting stabilized.Therefore,rill flow velocity can be effectively measured with leading edge method by multiplying the leading edge velocity with a correction coefficient of 0.80.This study provides a strategy to measure rill flow velocity for studies on soil erosion mechanisms.展开更多
在高速低密度风洞喷管流动中,振动温度出现冻结,与平动温度和转动温度产生了严重的非平衡现象。相关数值模拟结果中,振动温度完全冻结,而试验结果明显低于计算结果。为合理解释此现象,对数值模拟方法在低温条件下的应用进行分析,基于直...在高速低密度风洞喷管流动中,振动温度出现冻结,与平动温度和转动温度产生了严重的非平衡现象。相关数值模拟结果中,振动温度完全冻结,而试验结果明显低于计算结果。为合理解释此现象,对数值模拟方法在低温条件下的应用进行分析,基于直接模拟蒙特卡罗(direct simulation Monte Carlo,DSMC)方法中热力学非平衡模拟技术,对振动松弛碰撞数进行修正,给出了修正系数1×10^(-7),建立了低温振动非平衡流动数值模拟方法。利用该方法对低密度风洞M16喷管流场和10 N姿控发动机羽流流场开展数值模拟,得到了与试验结果相符合的振动温度。研究表明:在低温条件下,由于振动松弛碰撞数很大,气体分子很难发生振动松弛碰撞,振动能不能向平动能转化,振动温度完全冻结;通过修正,降低振动松弛碰撞数,增加振动松弛碰撞的概率,可以降低振动冻结温度,使得数值模拟结果与试验结果吻合。展开更多
文摘Flow velocity is a major parameter related to hillslope hydrodynamics erosion.This study aims to measure flow velocity over frozen and non-frozen slopes through leading edge method before being calibrated with accurate flow velocity to determine the correct coefficient for convenience of flow velocity measurement.Laboratory experiments were conducted on frozen and non-frozen soil slopes with flumes involving four slope gradients of 5°,10°,15°,and 20°and three flow rates of 1,2,and 4 L/min with a flume of 6 m long and 0.1 m wide.The measurements were made with a stopwatch to record the time duration that the water flow ran over the rill segments of 2,4 and 6 m long.Accurate flow velocity was measured with electrolyte trace method,under pulse boundary condition.The leading edge and accurate flow velocities were used to determine the correction coefficient to convert the former to the latter.Results showed that the correction coefficient on frozen soil slope was 0.81 with a coefficient of determination(R2)of 0.99.The correction coefficient on non-frozen soil slope was 0.79 with R2 of 0.98.A coefficient of 0.8 was applicable to both soil surface conditions.The accurate velocities on the four frozen black soil slopes were approximately 30%,54%,71%,and 91%higher than those on non-frozen soil slopes.By contrast,the leading edge flow velocities on the frozen soil slopes were 23%,54%,67%,and 84%higher than those on non-frozen soil slopes.The flow velocities on frozen soil slopes increased with flow rate at all four slopes,but they increased from 5 to 15°before getting stabilized.Therefore,rill flow velocity can be effectively measured with leading edge method by multiplying the leading edge velocity with a correction coefficient of 0.80.This study provides a strategy to measure rill flow velocity for studies on soil erosion mechanisms.
文摘在高速低密度风洞喷管流动中,振动温度出现冻结,与平动温度和转动温度产生了严重的非平衡现象。相关数值模拟结果中,振动温度完全冻结,而试验结果明显低于计算结果。为合理解释此现象,对数值模拟方法在低温条件下的应用进行分析,基于直接模拟蒙特卡罗(direct simulation Monte Carlo,DSMC)方法中热力学非平衡模拟技术,对振动松弛碰撞数进行修正,给出了修正系数1×10^(-7),建立了低温振动非平衡流动数值模拟方法。利用该方法对低密度风洞M16喷管流场和10 N姿控发动机羽流流场开展数值模拟,得到了与试验结果相符合的振动温度。研究表明:在低温条件下,由于振动松弛碰撞数很大,气体分子很难发生振动松弛碰撞,振动能不能向平动能转化,振动温度完全冻结;通过修正,降低振动松弛碰撞数,增加振动松弛碰撞的概率,可以降低振动冻结温度,使得数值模拟结果与试验结果吻合。
