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A biconcave particle suspended in a Poiseuille flow is investigated by the multiple-relaxation-time lattice Boltzmann method with the Galilean-invariant momentum exchange method. The lateral migration and equilibrium of the particle are similar to the Segre-Silberberg effect in our numerical simulations. Surprisingly, two lateral equilibrium positions are observed corresponding to the releasing positions of the biconcave particle. The upper equilibrium positions significantly decrease with the increasing Reynolds number, whereas the lower ones are almost insensitive to the Reynolds number. Interestingly, the regular wave accompanied by nonuniform rotation is exhibited in the lateral movement of the biconcave particle. It can be attributed to the fact that the biconcave shape in various postures interacts with the parabolic velocity distribution of the Poiseuille flow. A set of contours illustrate the dynamic flow field when the biconcave particle has successive postures in a rotating period.

A compact hydrophobic nanoparticle (HNP) adsorption layer, which has miro- and nano-dual structural properties like lotus leaf, can be built by adsorbing HNP on core surfaces. A slip velocity on the surface can be produced with the purpose of reducing the water resistance and increasing water injection rate. The results are of significance for the study of HNP drag reduction technology. In this paper we give a briefing of the super hydrophobic properties of the lotus leaf, mosquito legs, and striders leg. The strong hydrophobic surface preparation method with HNP adsorption layer is presented, and physical mechanism of strong hydrophobic surfaces with regular arrangement of HNPs is given. According to the real HNP adsorption core samples, the contact angle range is given, the calculation results accord well with experimental data. Core displacement experimental results show that the average drag reduction rate can be up to 94%.

Dual drag reduction mechanisms of water-based dispersion with nanoparticle is proposed. A contrastive study is take to verify the mechanism, in which the changes of surface microstructure and wettabilities of the core slices take place before and after treating by dispersion with hydrophobic nanoparticles and scouring by water. The results show that the surface of core slice which is treated by water-based dispersion with hydrophobic nanoparticles has strong hydrophilic property, and a compact nanoparticle adsorption layer forms on it. The nanoparticle adsorption layer still exists after scouring, but the core slice surface is changed into strong/super hydrophobic, reflecting that the surfactants which are adsorbed on the nanoparticles adsorption layer surface are gradually cleaned. The water-based dispersion with hydrophobic nanoparticles are mainly manifested as the chemical surfactant drag reduction effect during initial injection. With the injection continued, the mechanical drag reduction induced by the slip effect of super hydrophobic surface is reflected mainly. Core displacement results show that the water-phase effective permeability could increase about 84.3% on average. The results strongly confirm the dual drag reduction mechanism of the water-based dispersion with hydrophobic nanoparticles.