Elastic 'Ribbing' Instabilities in Fluid-Fluid Displacement Flows

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AbstractCTS-0089502B. Khomami, Washington UniversityThis is one of two identical proposals submitted by Washington University and Stanford University. A combined experimental and numerical study is proposed to examine the effect of elasticity on the stability of fluid-fluid displacement interfaces-sometimes known as the "ribbing" instability. Such instabilities limit either the speed or the quality of production of adhesive coatings in industrial processes. This is a collaborative effort between Bamin Khomami of Washington University and Eric Shaqfeh of Stanford University with the numerical part being carried out mainly in the former institution while the experimental part mainly at the latter institution. Preliminary experiments performed by the PI's showed the dramatic onset of such instabilities. It is hypothesized that the instability is caused by the unstable stress gradient created by the extensional finger flow near the displacing front. The research plan is to obtain quantitative experimental data of such instability flows using modern instrumentation, to carry out linear and nonlinear stability analysis of the flows, and full three-dimensional simulations of the unstable elastic fluid interfaces to test the hypothesis. In addition, the possibility of enhancing the stability of the system by introducing time-periodic parametric forcing will be examined by simulations.