Lamination and mixing in three fundamental flow sequences driven by electromagnetic body forces

Abstract

This article pursues the idea that the degree of striations, called lamination, could be engineered to complement stretching and to design new sequential mixers. It explores lamination and mixing in three new mixing sequences experimentally driven by electromagnetic body forces. To generate these three mixing sequences, Lorentz body forces are dynamically controlled to vary the flow geometry produced by a pair of local jets. The first two sequences are inspired from the "tendril and whorl" and "blinking vortex" flows. The third novel sequence is called the "cat's eyes flip." These three mixing sequences exponentially stretch and laminate material lines representing the interface between two domains to be mixed. Moreover, the mixing coefficient (defined as 1-σ(2)/σ(0)(2) where σ(2)/σ(0)(2) is the rescaled variance) and its rate grow exponentially before saturation. This saturation of the mixing process is related to the departure of the mixing rate from an exponential growth when the striations' thicknesses reach the diffusive length scale of the measurements or species and dyes. Incidentally, in our experiments, for the same energy or forcing input, the cat's eyes flip sequence has higher lamination, stretching, and mixing rates than the tendril and whorl and the blinking vortex sequences. These features show that bakerlike in situ mixers can be conceived by dynamically controlling a pair of local jets and by integrating lamination during stirring stages with persistent geometries. Combined with novel insights provided by the quantification of the lamination, this paper should offer perspectives for the development of new sequential mixers, possibly on all scales.

Quantifying spatial structure in experimental observations and agent-based simulations using pair-correlation functions

“…1(e) and 1(f). The evolution of such physical systems can be simulated using a range of frameworks including discrete random-walk-based methods [4][5][6][7][8][9][10] and other techniques [2,[11][12][13][14][15][16][17]. Quantifying the spatial structure predicted by such modeling frameworks is essential when we consider comparing the model prediction with an experimental image.…”

Effects of electromagnetic forcing on self-sustained jet oscillations

“…The use of this principle was reported in several publications, for instance to delay flow separations, 16,17 to increase heat transfer, 18,19 and to increase laminar a) Electronic mail: r.kalter@tudelft.nl mixing. [20][21][22] Electromagnetic actuators are used for the control of turbulent channel flow, 23,24 for the suppression of vortex shedding behind a cylinder, 25,26 and to prevent flow separation past an airfoil. [27][28][29] The effect of electromagnetic forcing on self-sustained oscillations of a confined jet issuing into a thin cavity is investigated experimentally using particle image velocimetry (PIV).…”

Viscous pumping inspired by flexible propulsion

“…However, a more in depth study is needed to assess the mixing capacity of the flow produced by the flexible flapper. In particular, some of the ideas discussed in the mixing literature by laminar jets (see for instance [36]) could be used to evaluate the mixing potential of the current setup. We hope that the proof-of-principle study carried out in this paper will encourage further work in this direction.…”