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Understanding and modeling flows over porous layers are of great industrial significance. To accurately solve the turbulent multi-scale flows on complex configurations, a rescaling algorithm designed for turbulent flows with the Chapman-Enskog analysis is proposed. The mesh layout and the detailed rescaling procedure are also introduced. Direct numerical simulations (DNSs) for a turbulent channel flow and a porous walled turbulent channel flow are performed with the three-dimensional nineteen-velocity (D3Q19) multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) to validate the accuracy, adaptability, and computational performance of the present rescaling algorithm. The results, which are consistent with the previous DNS studies based on the finite difference method and the LBM, demonstrate that the present method can maintain the continuity of the macro values across the grid interface and is able to adapt to complex geometries. The reasonable time consumption of the rescaling procedure shows that the present method can accurately calculate various turbulent flows with multi-scale and complex configurations while maintaining high computational efficiency. [ABSTRACT FROM AUTHOR]

The distribution and concentration of dissolved oxygen (DO) play important roles in aerobic heterotroph activities and some slow chemical reactions, and can affect the water quality, biological communities, and ecosystem functions of rivers and lakes. In this work, the transport of high Schmidt number DO at the sediment-water interface of spanwise oscillating flow is investigated. The volume-averaged Navier-Stokes (VANS) equations and Monod equation are used to describe the flow in the sediment layer and the sediment oxygen demand of microorganisms. The phase-averaged velocities and concentrations of different amplitudes and periods are studied. The dependence of DO transfer on the amplitude and period is analyzed by means of phase-average statistical quantities. It is shown that the concentration in the sediment layer is positively correlated with the turbulence intensity, and the DO concentration and penetration depth in the sediment layer increases when the period and amplitude of the oscillating flow increase. Moreover, in the presence of oscillating flow, a specific scaling relationship exists between the Sherwood number/oxygen consumption of aerobic heterotrophs and the Reynolds number. [ABSTRACT FROM AUTHOR]

The direct numerical simulation (DNS) is carried out for the incompressible viscous turbulent flows over an anisotropic porous wall. Effects of the anisotropic porous wall on turbulence modifications as well as on the turbulent drag reduction are investigated. The simulation is carried out at a friction Reynolds number of 180, which is based on the averaged friction velocity at the interface between the porous medium and the clear fluid domain. The depth of the porous layer ranges from 0.9 to 54 viscous units. The permeability in the spanwise direction is set to be lower than the other directions in the present simulation. The maximum drag reduction obtained is about 15.3% which occurs for a depth of 9 viscous units. The increasing of drag is addressed when the depth of the porous layer is more than 25 wall units. The thinner porous layer restricts the spanwise extension of the streamwise vortices which suppresses the bursting events near the wall. However, for the thicker porous layer, the wall-normal fluctuations are enhanced due to the weakening of the wall-blocking effect which can trigger strong turbulent structures near the wall. [ABSTRACT FROM AUTHOR]

Interaction between turbulence and particles is investigated in a channel flow. The fluid motion is calculated using direct numerical simulation (DNS) with a lattice Boltzmann (LB) method, and particles are tracked in a Lagrangian framework through the action of force imposed by the fluid. The particle diameter is smaller than the Kolmogorov length scale, and the point force is used to represent the feedback force of particles on the turbulence. The effects of particles on the turbulence and skin friction coefficient are examined with different particle inertias and mass loadings. Inertial particles suppress intensities of the spanwise and wall-normal components of velocity, and the Reynolds shear stress. It is also found that, relative to the reference particle-free flow, the overall mean skin-friction coefficient is reduced by particles. Changes of near wall turbulent structures such as longer and more regular streamwise low-speed streaks and less ejections and sweeps are the manifestation of drag reduction. [ABSTRACT FROM AUTHOR]

The effect of inertial particles with different specific heat on heat transfer in particle-laden turbulent channel flows is studied using the direct numerical simulation (DNS) and the Lagrangian particle tracking method. The simulation uses a two-way coupling model to consider the momentum and thermal interactions between the particles and turbulence. The study shows that the temperature fields display differences between the particle-laden flow with different specific heat particles and the particle-free flow, indicating that the particle specific heat is an important factor that affects the heat transfer process in a particle-laden flow. It is found that the heat transfer capacity of the particle-laden flow gradually increases with the increase of the particle specific heat. This is due to the positive contribution of the particle increase to the heat transfer. In addition, the Nusselt number of a particle-laden flow is compared with that of a particle-free flow. It is found that particles with a large specific heat strengthen heat transfer of turbulent flow, while those with small specific heat weaken heat transfer of turbulent flow. [ABSTRACT FROM AUTHOR]

The hydrate formation or dissociation in deep subsea flow lines is a challenging problem in oil and gas transport systems. The study of multiphase flows is complex while necessary due to the phase changes (i.e., liquid, solid, and gas) that occur with increasing the temperature and decreasing the pressure. A one-dimensional multiphase flow model coupled with a transient hydrate kinetic model is developed to study the characteristics of the multiphase flows for the hydrates formed by the phase changes in the pipes. The multiphase flow model is derived from a multi-fluid model, while has been widely used in modelling multiphase flows. The heat convection between the fluid and the ambient through the pipe wall is considered in the energy balance equation. The developed multiphase flow model is used to simulate the procedure of the hydrate transport. The results show that the formation of the hydrates can cause hold-up oscillations of water and gas. [ABSTRACT FROM AUTHOR]

The direct numerical simulation (DNS) of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed. The focus of this paper is on the modulation of the particles on turbulent thermal statistics in the particle-laden flow with three Prandtl numbers ( Pr = 0.71, 1.5, and 3.0) and a shear Reynolds number ( Re = 180). Some typical thermal statistics, including normalized mean temperature and their fluctuations, turbulent heat fluxes, Nusselt number and so on, are analyzed. The results show that the particles have less effects on turbulent thermal fields with the increase of Prandtl number. Two reasons can explain this. First, the correlation between fluid thermal field and velocity field decreases as the Prandtl number increases, and the modulation of turbulent velocity field induced by the particles has less influence on the turbulent thermal field. Second, the heat exchange between turbulence and particles decreases for the particle-laden flow with the larger Prandtl number, and the thermal feedback of the particles to turbulence becomes weak. [ABSTRACT FROM AUTHOR]