An anomalous curved jet emerging from laminar Poiseuille flow (gel-like behavior and breakdown of transparent shear-induced structures in dilute cationic surfactant solutions)

Abstract

A laminar Poiseuille flow of a dilute cationic surfactant solution produces threadlike shear-induced structures (SISs) that are dispersed densely within a near-wall layer. This near-wall SIS layer behaves like a coherent gel within the jet. When the jet impinges on the wall, it is found to anomalously curve aside from the wall rather than impinging straight. With an increase in the flow rate, this curved jet becomes a straight impinging jet, and the SIS layer is broken down by compression at the wall stagnation point. The normal stress at the stagnation point is investigated as the critical condition for SIS breakdown and is represented as a function of the wall shear stress of the channel flow. The critical normal stress increases with the wall shear stress in the channel flow and then decreases rapidly above the critical wall shear stress. In addition to the gel-like coherent characteristics of the SIS layer, the macroscopic apparent viscosity of the SIS layer is investigated and estimated to be 2.5–5 mPa s in the channel flow. The SIS layer shows a rather low macroscopic apparent viscosity despite its gel-like coherent behavior.