90°方形弯管内部流动稳定性研究

Stability Study of Flow in a 90° Square Bend

利用能量梯度理论研究了90°方形截面弯管内部层流流动的稳定性。研究发现当雷诺数大于338时,随着流体流向弯曲段,能量梯度函数K值逐渐增大,流动发生失稳,截面上形成一对二次涡。在弯曲段出口处,总压在截面上的分布发生严重扭曲,使得此处的K值有最大值,引起流动再次失稳,导致了截面上2个二次涡向4个二次涡的转变。随后,K值保持较高水平,导致了4个二次涡到8个二次涡的转变。而在雷诺数低于338时,由于K值较小,横截面上只有1对二次涡,没有发生二次涡的分裂。

The energy gradient theory is used to analyze the stability of laminar flow in a 90degree bend with square cross-section.It is found that the value of the energy gradient function K increases with fluid entering the curved section when Reynolds number is higher than 338,causing flow instability and forming a pair of secondary vortices.At the exit of the curved section,the total pressure distribution in the cross-section presents serious distortion,generating a maximum of K.The maximum of K leads to flow instability,then the number of secondary vortex changes from two to four.With the flow going ahead,the maximum of K keeps high value,resulting in the transition of four vortices to eight vortices.When the Reynolds number is lower than 338,there is only one pair of vortices always in the bend due to the low value of K.