Upstream wall vortices in viscoelastic flow past a cylinder
Upstream wall vortices in viscoelastic flow past a cylinder
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DOI：
10.1039/d2sm00418f
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发表时间：
2022-06-13
期刊：
影响因子：
3.4
通讯作者：
Shen, Amy Q.
中科院分区：
文献类型：
--
作者：
Hopkins, Cameron C.;Haward, Simon J.;Shen, Amy Q.
We report a novel inertia-less, elastic flow instability for a viscoelastic, shear-thinning wormlike micellar solution flowing past a microcylinder in a channel with blockage ratio B-R = 2R/W = 0.5 and aspect ratio alpha = H/W approximate to 5, where R approximate to 100 mu m is the cylinder radius, W is the channel width, and H is the channel height. The instability manifests upstream of the cylinder and changes form with increasing Weissenberg number over the range 0.5 less than or similar to Wi = U lambda/R less than or similar to 900, where U is the average flow velocity and lambda is the terminal relaxation time of the fluid. Beyond a first critical Wi, the instability begins as a bending of the streamlines near the upstream pole of the cylinder that breaks the symmetry of the flow. Beyond a second critical Wi, small, time-steady, and approximately symmetric wall-attached vortices form upstream of the cylinder. Beyond a third critical Wi, the flow becomes time dependent and pulses with a characteristic frequency commensurate with the breakage timescale of the wormlike micelles. This is accompanied by a breaking of the symmetry of the wall-attached vortices, where one vortex becomes considerably larger than the other. Finally, beyond a fourth critical Wi, a vortex forms attached to the upstream pole of the cylinder whose length fluctuates in time. The flow is highly time dependent, and the cylinder-attached vortex and wall-attached vortices compete dynamically for space and time in the channel. Our results add to the rapidly growing understanding of viscoelastic flow instabilities in microfluidic geometries.
