边界层变化对聚合物湍流减阻流动特性的影响

Influence of boundary layer variation on turbulent drag reduction flow characteristics of polymer

在流体中添加高分子聚合物不仅会产生减阻效应,还会降低传热性能。若将聚合物减阻应用于供冷、供热系统,可降低传输过程中的流动阻力和热量损失,从而实现能耗的节约。文章以壁湍流理论为依据,用模拟的方法研究了在圆管中设置不同高度的V形肋条对高聚物减阻效果的影响。结果表明:在管道内设置肋条会改变原有的边界层结构,肋高的增加会加大对边界层的破坏;不同肋高及减阻参数对湍动能和雷诺应力的影响趋势一致;当肋条高度增加到大于黏性底层厚度时,聚合物的减阻率降低,减阻效果减弱,且肋条高度越大,减阻效果所受影响越大;线性底层内的边界层变化对聚合物湍流减阻无影响,当缓冲层没有受到扰动和破坏时,聚合物减阻作用不受影响,而当缓冲层受到影响时,聚合物减弱了减阻作用。

Adding polymer in the fluid will not only reduce the resistance,but also reduce the heat transfer performance.If polymer drag reduction is applied to the cooling and heating system,the flow resistance and heat loss in the transmission process can be greatly reduced,thus saving energy consumption.Based on the theory of wall turbulence,the effect of V-shaped riblets with different heights in the pipeline on the drag reduction effect of polymer is simulated.The simulation results show that setting riblets in the original pipeline will change the original boundary layer structure.The increase of riblet height will increase the damage to the boundary layer.The effects of different riblet heights and drag reduction parameters on turbulent kinetic energy and Reynolds stress are consistent.When the riblet height is greater than the thickness of the viscous bottom layer,the turbulence kinetic energy and Reynolds stress near the wall are more intense,while the drag reduction rate of polymer decreases and the drag reduction effect is weakened.The higher the riblet height,the greater the influence on drag reduction effect.The variation of the boundary layer in the linear bottom layer has no effect on the polymer turbulent drag reduction.When buffer layer is not disturbed and destroyed,polymer drag reduction is not affected.When the buffer layer is affected,the polymer drag reduction will be weakened.