Department of Physics of Complex Systems, Weizmann Institute of Science, 76100, Rehovot, Israel.
Institute of Science and Technology Austria, Am Campus 1, 3400, Klosterneuburg, Austria.
Nat Commun. 2019 Feb 8;10(1):652. doi: 10.1038/s41467-019-08551-0.
Speed of sound waves in gases and liquids are governed by the compressibility of the medium. There exists another type of non-dispersive wave where the wave speed depends on stress instead of elasticity of the medium. A well-known example is the Alfven wave, which propagates through plasma permeated by a magnetic field with the speed determined by magnetic tension. An elastic analogue of Alfven waves has been predicted in a flow of dilute polymer solution where the elastic stress of the stretching polymers determines the elastic wave speed. Here we present quantitative evidence of elastic Alfven waves in elastic turbulence of a viscoelastic creeping flow between two obstacles in channel flow. The key finding in the experimental proof is a nonlinear dependence of the elastic wave speed c on the Weissenberg number Wi, which deviates from predictions based on a model of linear polymer elasticity.
声波在气体和液体中的传播速度取决于介质的可压缩性。还有另一种非弥散波，其波速取决于应力而不是介质的弹性。一个著名的例子是阿尔文波，它在磁场中传播的等离子体中传播，速度由磁场张力决定。在充满磁场的聚合物稀溶液的流动中，已经预测出了阿尔文波的弹性类似物，其中拉伸聚合物的弹性应力决定了弹性波的速度。在这里，我们在通道流中两个障碍物之间的粘弹性蠕动流的弹性湍流中，给出了弹性阿尔文波的定量证据。实验证明的关键发现是弹性波速度 c 对魏森贝格数 Wi 的非线性依赖关系，这与基于线性聚合物弹性模型的预测不同。
