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Existing models of two-phase fluctuating velocity correlation moments are unsatisfactory because of their inability to clearly identify the dependency of two-phase velocity covariance on fluid- and particle-phase velocity second moments. This is especially true of wall-bounded turbulent flows. In this paper, the statistical fluctuating velocity of both phases in particle-laden turbulent channel flows were obtained numerically by means of direct numerical simulation (DNS) coupled to the Lagrangian particle trajectory method. The effects of particle Stokes number on the scaling of two-phase fluctuating velocity correlation moments were analyzed considering effects of flow inhomogeneity. An improved two-phase correlation closure model of exponential decay with emphasis on the particle-phase kinetic energy was then proposed based on the results of an evaluation of five existing models. This new model was found to be better than previous models, which used local equilibrium assumption. The present investigations may facilitate understanding of two-phase flow physics and the construction of models capable of predicting the movements of particle-laden turbulent flows accurately using Reynolds-averaged Navier–Stokes (RANS) methods.

Nonparticulate continuum descriptions allow for computationally efficient modeling of suspension flows at scales that are inaccessible to more detailed particulate approaches. It is well known that the presence of particles influences the effective viscosity of a suspension and that this effect has thus to be accounted for in macroscopic continuum models. The present paper aims at developing a nonparticulate model that reproduces not only the rheology but also the cell-induced velocity fluctuations, responsible for enhanced diffusivity. The results are obtained from a coarse-grained blood model based on the lattice Boltzmann (LB) method. The benchmark system comprises a flow between two parallel plates with one of them featuring a smooth obstacle imitating a stenosis. Appropriate boundary conditions are developed for the particulate model to generate equilibrated cell configurations mimicking an infinite channel in front of the stenosis. The averaged flow field in the bulk of the channel can be described well by a nonparticulate simulation with a matched viscosity. We show that our proposed phenomenological model is capable to reproduce many features of the velocity fluctuations.

Large eddy simulation was applied to simulate the compressible flow past multiple wall-mounted rectangular cylinders in a channel flow. The dynamic sub-grid stress model was employed to approximate the sub-grid scale effects. For flow past single wall-mounted cylinder, our calculated results agree well with the results of both previous experimental and numerical results which showed the formation and diffusion of vortexes around the cylinder. Flow past two wall-mounted cylinders has also been simulated numerically and our numerical results disclosed the formation of the vortex street behind the second cylinder and the developing process of flow field, which is important for practical engineering application.

To explore the rheological property in turbulent channel flow of fiber suspensions, the equation of probability distribution function for mean fiber orientation and the Reynolds averaged Navier-Stokes equation with the term of additional stress resulted from fibers were solved with numerical methods to get the distributions of the mean velocity and turbulent kinetic energy. The simulation results show that the effect of fibers on turbulent channel flow is equivalent to an additional viscosity. The turbulent velocity profiles of fiber suspension become gradually sharper by increasing the fiber concentration and/or decreasing the Reynolds number. The turbulent kinetic energy will increase with increasing Reynolds number and fiber concentration.

The effect of spanwise alternatively distributed strips (SADS) control on turbulent flow in a plane channel has been studied by direct numerical simulations to investigate the characteristics of large-scale streamwise vortices (LSSVs) induced by small-scale active wall actuation, and their potential in suppressing flow separation. SADS control is realized by alternatively arranging out-of-phase control (OPC) and in-phase control (IPC) wall actuations on the lower channel wall surface, in the spanwise direction. It is found that the coherent structures are suppressed or enhanced alternatively by OPC or IPC, respectively, leading to the formation of a vertical shear layer, which is responsible for the LSSVs’ presence. Large-scale low-speed region can also be observed above the OPC strips, which resemble large-scale low-speed streaks. LSSVs are found to be in a statistically-converged steady state and their cores are located between two neighboring OPC and IPC strips. Their motions contribute significantly to the momentum transport in the wall-normal and spanwise directions, demonstrating their potential ability to suppress flow separation.

Nanofluids and hybrid nanofluids enhance the transfer of heat with low nanoparticle concentration. Tri-hybrid nanofluids combine different nanoparticles (NPs) to further increase the performance of base fluids. Tri-hybrid nanofluids have significant uses in several industries, including electronic cooling, heat transport, biomedical engineering as well as energy storage systems. This study investigates the thermal performance of tri-hybrid nanofluid in the existence of a magnetic field and porous saturated space along with copper (Cu), aluminium oxide (Al₂O₃), and titanium dioxide (TiO₂) NPs dispersed in base fluid, i.e. water (H₂O) flowing through a vertical channel by convection. The resultant partial differential equations based on Atangana–Baleanu time-fractional derivative (having non-singular and non-local kernel) are solved using the Laplace transform along with the appropriate physical conditions. The Stehfest as well as Tzou’s numerical approaches are then utilized to compute the Laplace inverse, to check the validity of obtained solutions and to get the graphical representations of, concentration, energy, and velocity fields. The results show that tri-hybrid nanofluids have advanced thermal as well as momentum characteristics compared to nanofluids and hybrid nanofluids.

This is an attempt to investigate swallowing of a food bolus through oesophagus by modelling it as an unsteady peristaltic transport of Maxwell and magnetohydrodynamic (MHD) fluids in channels of finite length. The walls of the channels are subjected to progressive transverse contraction waves so that the natural oesophageal wall contractions are matched. The analysis is carried out in non-dimensional form by using long wavelength approximations. The expressions for axial and transverse velocities are derived and pressure across a wavelength is estimated. The reflux limit is determined for both the fluids. Mechanical efficiency for MHD fluids is also obtained. Physical interpretations reveal the behaviour of the flows of masticated viscoelastic food materials such as bread, white eggs etc. and saline water that is represented by MHD model in the oesophagus. It is found that fluids represented by Maxwell fluid are more swallow-friendly than Newtonian fluids while normal water is easier to swallow than saline water which is an MHD fluid. It is also revealed that relaxation time, a parameter of Maxwell model, has no effects on local wall shear stress and reflux limit whereas magneto-hydrodynamic parameters make the fluid more prone to flow reversal. It is found that if the transverse magnetic field and the electric conductivity increase, the pumping machinery requires more pressure for pushing the fluid forward. In other words, pumping has to work more efficiently. Finally, it is revealed that the peaks of pressure are identical, in case, an integral number of waves propagate along the channel while the peaks are of unequal size in the non-integral case.

We consider equations describing a barotropic inviscid flow in a channel with topography effects and beta-plane approximation of Coriolis force, in which a large-scale mean flow interacts with smaller scales. Gibbsian measures associated to the first integrals energy and enstrophy are Gaussian measures supported by distributional spaces. We define a suitable weak formulation for barotropic equations, and prove existence of a solution preserving Gibbsian measures, thus providing a rigorous infinite-dimensional framework for the equilibrium statistical mechanics of the model.

Lattice Boltzmann Method (LBM) simulations for turbulent flows over fractal and non-fractal obstacles are presented. The wake hydrodynamics are compared and discussed in terms of flow relaxation, Strouhal numbers and wake length for different Reynolds numbers. Three obstacle topologies are studied, Solid (SS), Porous Regular (PR) and Porous Fractal (FR). In particular, we observe that the oscillation present in the case of the solid square can be annihilated or only pushed downstream depending on the topology of the porous obstacle. The LBM is implemented over a range of four Reynolds numbers from 12,352 to 49,410. The suitability of LBM for these high Reynolds number cases is studied. Its results are compared to available experimental data and published literature. Compelling agreements between all three tested obstacles show a significant validation of LBM as a tool to investigate high Reynolds number flows in complex geometries. This is particularly important as the LBM method is much less time consuming than a classical Navier–Stokes equation-based computing method and high Reynolds numbers need to be achieved with enough details (i.e., resolution) to predict for example canopy flows.

In a stably stratified turbulent flow, computation based on Boussinesq assumption (uniform fluid properties) for strongly temperature dependent fluid properties like viscosity and thermal conductivity results in an inaccurate estimation of momentum and heat transfer coefficients. Role of thermo-fluid properties adversely affect the turbulent structures and shows evidence of relaminarization at the hot wall of the channel. In this article the role of internal gravity wave, its behavior in Bousinesq and non-Boussinesq situation is elaborated via turbulent structure and energy spectra for turbulent channel flow of air with varying viscosity and thermal conductivity. Due to temperature dependent properties internal gravity wave shifted towards hot wall from the core of the channel.