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An experimental study on immiscible viscous fingering (VF) with chemical reaction is described, whereby a surfactant produced in a radial Hele-Shaw cell results in a decrease in interfacial tension. The surfactant is formed at the interface between alkaline solution (sodium hydroxide) and a long-chain fatty acid (linoleic acid). This topic is closely related to alkaline flooding, which is an enhanced oil recovery method. The reaction was found to have two opposing effects on VF depending on the flow rate, namely, narrowing and widening of the fingers. Moreover, the influences of the reaction on VF evolution can be categorized into five different types based on the effects appearing in VF evolution and the fingering width and area at the maximum observation region. Possible mechanisms for each type are proposed, and an argument based on scaling of the VF properties using dimensionless numbers gives support to the proposed mechanisms. This dual role of the reaction in immiscible VF evolution may contribute to establishing optimal conditions for alkaline flooding. Moreover, the finding that one chemical reaction has two opposing effects on flow is of value from the standpoint of fundamental studies of reacting flow dynamics.

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Direct numerical simulation of hydrogen-air turbulent premixed flames propagating in homogeneous isotropic turbulence is conducted to clarify turbulence-flame interaction in turbulent premixed flames. A detailed kinetic mechanism which includes 12 species and 27 elementary reactions is used to represent the H2-O2-N2 reaction in turbulence. Figure 1 shows tube-like coherent fine scale eddies and heat release rate. It is shown that the fine scale structure of turbulent premixed flames is significantly affected by the coherent fine scale eddies in turbulence. Figure 2 shows distributions of heat release rate, O atom and OH radical on a typical cross section with the coherent fine scale eddies. The relatively strong coherent fine scale eddies can survive behind the flame front and they are perpendicular to the flame front where heat release rate increases. Most of the coherent fine scale eddies near the flame front tends to be parallel to the flame front and enhance the chemical reaction. Figure 2 Modification of local flame structure due to coherent fine scale eddies in turbulence. (a) Heat release rate (b) O atom (c) OH radical Figure 1 Coherent fine scale eddies in unburnt turbulence (green) and high heat release rate region (yellow) in a hydrogen-air turbulent premixed flame.

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