定优胶溶液狭缝喷射减阻实验研究

EXPERIMENTAL STUDY ON DRAG REDUCTION CHARACTERISTICS OF DIUTAN GUM SOLUTION BY SLIT INJECTION

定优胶具有比柔性聚合物更优越的抗剪切效果,是一种新型高分子聚合物减阻添加剂,目前对其研究仍相对缺乏.这里通过开展定优胶流变和管内狭缝喷射减阻实验,分析了流变特性与减阻行为之间的联系,并从其喷射扩散角度解释了其减阻规律变化的原因.实验结果表明,定优胶溶液为剪切变稀流体,会发生黏性到弹性转变,且转变点与温度无关,仅随浓度增加而前移;定优胶减阻率随水流速度(雷诺数)呈先增后降趋势,但随喷射速率单调递增;相较于喷射纯水,定优胶溶液在流场中扩散缓慢,且喷射速率越高,壁面附近集聚越明显.同时,定优胶溶液喷射减阻的变化与其扩散规律相吻合:当流速较小时,定优胶溶液扩散不充分,呈非均匀聚集态,未能充分发挥其湍流抑制效果,减阻较弱;随流速增加,水流的剪切拖拽作用增强了定优胶的扩散均匀程度,进而提升湍流抑制效果,减阻率上升;但当流速过大时,定优胶的快速扩散造成其浓度被大幅稀释,且近壁区过大剪切率可能已造成部分长链分子断裂,致使减阻效果下降.

Diutan gum(DG)is a new type of polymer additive that can greatly reduce turbulence resistance.Compared with PEO,PAM and other flexible polymers,DG has significant shear resistance.However,there are relatively few studies on its drag reduction performance at present.In this paper,the relationship between the rheological characteristics of DG and its drag reduction behavior is analyzed by testing the rheological characteristics of DG,the law of drag reduction by in-tube injection and the process of spray diffusion,and the reasons for the change of its drag reduction law are explained from the perspective of spray diffusion.The results show that DG solution is a shear thinning fluid.The viscosity-elastic transition occurs and the transition point is independent of temperature,only moves forward with the increase of concentration.The drag reduction effect of DG increases firstly and then decreases with The Reynolds number,and increases monotonically with the injection rate.Compared with pure water injection,DG solution diffuses slowly in the flow field,and the higher the injection rate,the more obvious the agglomeration near the wall surface.Combined with the observation of jet diffusion of DG solution,it can be seen that when the flow rate is small,DG solution is not fully diffused,but in an uneven aggregation state,which does not give full play to its turbulence inhibition effect and has weak drag reduction.With the increase of flow velocity,the flow shear rate increases,the diffusion of DG is gradually uniform,the turbulence inhibition effect is enhanced,and the drag reduction rate increases.However,when the flow rate is too high,the concentration of DG is seriously diluted,and the shear rate in the near wall area is too high,which may cause the fracture of long chain molecules,resulting in the decrease of drag reduction effect.