粘弹性流体旋转流实验研究

Experimental study on free-surface swirling flow of viscoelastic fluid

利用粒子图像测速仪(PIV)对圆筒形容器内有自由表面变形的粘弹性流体旋转流动进行了实验研究.旋转流动由等速旋转的容器底面来驱动.实验工质为CTAC(十六烷基三甲基氯化铵界面活性剂)水溶液.测量了水、40×10-6、60×10-6和200×10-6CTAC水溶液在弗鲁德数为2.59至16.3范围内的旋转流动.PIV用来测量子午面内的二次流场,并从PIV图像中抽取自由面高度.结果表明在相似的弗鲁德数下,相比于水流CTAC水溶液旋转流动自由表面中心处的凹陷深度降低,随着溶液浓度或粘弹性升高,子午面内右上角的惯性涡被压缩且强度变得越来越弱.通过与水流动比较并做力平衡分析,定量估算了CTAC水溶液的第一正应力差或弱粘弹性.

By using a particle image velocimetry （PIV）, an experimental study was performed on the swirling flow of viscoelastic fluid with deformed free surface in a cylindrical container. The swirling flow was driven by the rotating bottom wall with constant rotation speed. The tested fluid was an aqueous solution of CTAC （ cetyltrimethyl ammonium chloride）. Water as well as CTAC solution flows of 40 ×10^-6, 60×10^-6 and 200×10^-6 were tested at Froude numbers ranging from 2.59 to 16. 3. PIV was used to measure the secondary velocity field in the meridional plane and the deformed free-surface level was extracted from the PIV images. Results show that at a similar Froude number, the depth of the dip formed at the center of the free surface is decreased for CTAC solution flow compared with water flow. The inertia-driven vortex at the up-right comer in the meridional plane becomes weaker and weaker with the increase of solution concentration or viscoelasticity. Through analyzing the overall force balance compared with water flow, the first normal stress difference or the weak viscoelasticity was estimated quantitatively for the dilute CTAC solution flows.