The optimal transient growth process of perturbations driven by the pressure gradient is studied in a turbulent pipe flow. A new computational method is proposed, based on the projection operators which project the go...The optimal transient growth process of perturbations driven by the pressure gradient is studied in a turbulent pipe flow. A new computational method is proposed, based on the projection operators which project the governing equations onto the sub- space spanned by the radial vorticity and radial velocity. The method is validated by comparing with the previous studies. Two peaks of the maximum transient growth am- plification curve are found at different Reynolds numbers ranging from 20 000 to 250 000. The optimal flow structures are obtained and compared with the experiments and DNS results. The location of the outer peak is at the azimuthal wave number n = 1, while the location of the inner peak is varying with the Reynolds number. It is observed that the velocity streaks in the buffer layer with a spacing of 100δv are the most amplified flow structures. Finally, we consider the optimal transient growth time and its dependence on the azimuthal wave length. It shows a self-similar behavior for perturbations of different scales in the optimal transient growth process.展开更多
为探究弹性管道与黏弹性管道串联混合连接的管道系统瞬变流压力波动的影响规律,设计并搭建了弹性/黏弹性串联混合管道系统瞬变流实验台,分别是镀锌钢管、镀锌钢管与聚丙烯(polypropylene,PPR)管混合管和镀锌钢管与高密度聚乙烯(high den...为探究弹性管道与黏弹性管道串联混合连接的管道系统瞬变流压力波动的影响规律,设计并搭建了弹性/黏弹性串联混合管道系统瞬变流实验台,分别是镀锌钢管、镀锌钢管与聚丙烯(polypropylene,PPR)管混合管和镀锌钢管与高密度聚乙烯(high density polyethylene,HDPE)管混合管。在不同初始流量情况下,分别对3种管道系统进行了瞬变流实验,基于实验数据,对黏弹性管道瞬变流模型结合一维拟稳态摩阻模型的参数进行校核,并提出了混合管道瞬变流参数校核方法。结果表明:使用黏弹性管道替换部分弹性管道会使得瞬变流压力波峰值衰减幅度下降,钢管/PPR混合管道相比钢管/HDPE混合管道具有更大的下降幅度。此外,应用一维拟稳态摩阻模型可以较准确地模拟混合管道瞬变流的压力波动过程,本文所提出的混合管道瞬变流参数校核方法可简便且准确地校核混合管道瞬变流参数,为工程中混合管道瞬变流的数值计算提供参考依据。展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.11322221,11132005,and 11490551)
文摘The optimal transient growth process of perturbations driven by the pressure gradient is studied in a turbulent pipe flow. A new computational method is proposed, based on the projection operators which project the governing equations onto the sub- space spanned by the radial vorticity and radial velocity. The method is validated by comparing with the previous studies. Two peaks of the maximum transient growth am- plification curve are found at different Reynolds numbers ranging from 20 000 to 250 000. The optimal flow structures are obtained and compared with the experiments and DNS results. The location of the outer peak is at the azimuthal wave number n = 1, while the location of the inner peak is varying with the Reynolds number. It is observed that the velocity streaks in the buffer layer with a spacing of 100δv are the most amplified flow structures. Finally, we consider the optimal transient growth time and its dependence on the azimuthal wave length. It shows a self-similar behavior for perturbations of different scales in the optimal transient growth process.
文摘为探究弹性管道与黏弹性管道串联混合连接的管道系统瞬变流压力波动的影响规律,设计并搭建了弹性/黏弹性串联混合管道系统瞬变流实验台,分别是镀锌钢管、镀锌钢管与聚丙烯(polypropylene,PPR)管混合管和镀锌钢管与高密度聚乙烯(high density polyethylene,HDPE)管混合管。在不同初始流量情况下,分别对3种管道系统进行了瞬变流实验,基于实验数据,对黏弹性管道瞬变流模型结合一维拟稳态摩阻模型的参数进行校核,并提出了混合管道瞬变流参数校核方法。结果表明:使用黏弹性管道替换部分弹性管道会使得瞬变流压力波峰值衰减幅度下降,钢管/PPR混合管道相比钢管/HDPE混合管道具有更大的下降幅度。此外,应用一维拟稳态摩阻模型可以较准确地模拟混合管道瞬变流的压力波动过程,本文所提出的混合管道瞬变流参数校核方法可简便且准确地校核混合管道瞬变流参数,为工程中混合管道瞬变流的数值计算提供参考依据。
