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Atmospheric boundary layer (ABL) flow over multiple-hill terrain is studied numerically. The spectral vanishing viscosity (SVV) method is employed for implicit large eddy simulation (ILES). ABL flow over one hill, double hills, and three hills are presented in detail. The instantaneous three-dimensional vortex structures, mean velocity, and turbulence intensity in mainstream and vertical directions around the hills are investigated to reveal the main properties of this turbulent flow. During the flow evolution downstream, the Kelvin-Helmholtz vortex, braid vortex, and hairpin vortex are observed sequentially. The turbulence intensity is enhanced around crests and reduced in the recirculation zones. The present results are helpful for understanding the impact of topography on the turbulent flow. The findings can be useful in various fields, such as wind energy, air pollution, and weather forecasting. [ABSTRACT FROM AUTHOR]

The effect of Stokes number on the kinetic energy (KE) budget in particle-laden turbulent channel flows is examined by conducting two-way coupled direct numerical simulations using the Eulerian-Lagrangian approach. The friction Reynolds number of the single phase channel flow is Reτ = 180, the particle mass loading and volume fraction are φm = 0.2, φv ≈ 10−4, and the Stokes numbers range from St+ = 14–92. The statistics show that due to the presence of solid particles, the mean velocity is reduced in the vicinity of the wall but enhanced in the outer region, and the off-streamwise intensity of fluctuated velocity and the Reynolds stress are reduced in the whole channel. The analysis on the budgets of turbulent kinetic energy (TKE) finds that the presence of particles induces a significant reduction on both the production and dissipation rates. With increasing Stokes number St+, both the production and dissipation rates exhibit non-monotonical trends, i.e., both initially decrease for St+ < 40 and then transit to growth after St+ > 40. This suggests that the particle-induced suppression on TKE production and dissipation is the strongest nearly at St+ = 40. It is also found that particles act as an additional sink/source term in the budgets of both mean-flow kinetic energy (MKE) and TKE. In addition, we investigate the influence of St+ on the "zero point" which indicates the balance of exchanging energy between the particle and fluid phases. It is shown that with increasing St+, the "zero point" moves toward the wall, suggesting that the position of perfect following between particle and fluid is closer to the wall with larger St+. The present results reveal the Stokes number effects on the spatial transport mechanisms of MKE, TKE in turbulent channel flows laden with inertial particles. [ABSTRACT FROM AUTHOR]

The tuning of turbulent Rayleigh-Bénard (RB) convection in a box is realized numerically by designed rough element arrangement. Considering the nonlinear dynamics of the thermal turbulence system, five models with rough elements of different widths and the same height are proposed to tune the fluid flow heat-transport capacity. Numerical simulations are performed using spectral element method for Rayleigh number in the range 106 ≤ Ra ≤ 109 and a fixed Prandtl number Pr = 0.7. It is found that heat transport is enhanced for large roughness widths as the interaction between the large-scale circulation and secondary flows inside the cavity regions between the rough elements promotes the eruptions of thermal plumes, but is suppressed for small ones as more heat are trapped inside the cavities. In all the rough models studied, different scaling exponents for the heat transport are identified and the influences of roughness arrangement on flow structure are studied. [ABSTRACT FROM AUTHOR]

The energy transfer and dissipation as well as the turbulent structures in a lid-driven cavity flow with porous walls are investigated via the lattice Boltzmann method, with direct numerical simulation (DNS) for an isothermal incompressible flow for which the Reynolds number (Re) is 50 000. A generalized Navier-Stokes equation with the Brinkman-Forchheimer-extended Darcy model is implemented, in which the presence of permeable walls is taken into account. This study focuses on the modulations of the flow field due to porous walls, by comparing with the results from the cavity flow bounded with smooth walls. Firstly, we derived the exact expression of the kinetic energy dissipation rate in a cavity to study the budget balance of the induced and dissipated kinetic energy. By decomposing the total kinetic energy dissipation into the componential contributions of the viscous and porous medium layer, we found that the kinetic energy dissipated in the thin porous layer occupies 37% of the total driven lid-induced kinetic energy in the present parameters. Then we found that the time-averaged kinetic energy, turbulent kinetic energy (TKE), as well as the strength of the large-scale energy-containing eddy, and secondary eddies are significantly attenuated. Furthermore, it is found that the momentum and kinetic energy transfer near the corners are vastly decreased. Finally, the space-time velocity correlation functions are also provided to examine the decorrelation property of small eddies by means of convection and distortion motions in the cavity turbulent field. [ABSTRACT FROM AUTHOR]

In this paper, an explicit low-storage simplified M — stage Runge-Kutta (SRK) scheme for high Reynolds-number incompressible flows is presented. In the SRK scheme, the Poisson equation is solved only once in the final substage of each time step. By taking advantage of the SRK scheme and the advanced hybrid MPI+MPI model, we have developed an efficient parallel solver for buoyancy-driven turbulent flow. The spatial and temporal accuracies of the solver are validated with Taylor-Green vortex flow. Both the RK and SRK schemes are implemented for the simulation of turbulent Rayleigh-Bénard convection as well as Rayleigh-Taylor flow. The results show that the SRK scheme can save approximately 20% of the computation time. [ABSTRACT FROM AUTHOR]