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• Using an equilibrium wall model for nonequilibrium flows is assessed. • Flows studied in 90° bent pipes with/without particles for the first time. • Spalding's law works acceptably with separated and particulate bent pipe flows. • Particle deposition efficiency accurately predicted at Stokes numbers more than 0.5. • Lower accuracy of WMLES at lower Stokes numbers similar to that of the standard LES. Wall-modeled large eddy simulation (WMLES) has been proven to be a cost-effective approach capable of resolving turbulence up to certain resolutions. Among the simplest wall models used are the equilibrium wall models, assuming the pressure gradient and convective terms balance out in the momentum equations. There is a lack of studies to assess the performance of these standard wall models in internal turbulent flows including separation regions with/without particles. Regarding this research gap, we have conducted WMLES of incompressible turbulent flows, to the authors' knowledge, for the first time, in 90° bent pipes with and without particles using an algebraic equilibrium wall model (Spalding's function). A pipe flow simulation was conducted to confirm the simulation setup and assess the sensitivity with respect to the modeling parameters. In each case, comparisons are made with experiment or direct numerical simulation (DNS), and depending on the case, with other existing simulation methods in the literature: WMLES, standard (wall-resolving) LES, and Reynolds stress model (RSM) for Reynolds-averaged Navier-Stokes (RANS) simulations. Despite the controversy on the performance of equilibrium wall models in nonequilibrium flows, our results show acceptable accuracy of this type of wall models. Specifically in the bent pipe flow with particles, WMLES succeeded in predicting particle deposition efficiency at Stokes numbers greater than 0.5, but obtained less accurate results for smaller Stokes numbers. The WMLES errors were, however, on par with those of the standard LES employed with a tenfold higher grid cell count. Improved results would be expected if combined with auxiliary mechanisms such as stochastic models. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive theoretical study on the dynamical behavior of natural convection flow in the confined region between horizontal half-cylinders. For this purpose, a low-order spectral model with three modes will produce for the fluid flow system using the Galerkin technique. It proved that the generated model is physically meaningful, as it conserves energy in the dissipationless limit and has bounded solutions in the phase space. Analytical procedures indicate that the system has three stationary points and the onset of instability in the flow is when the Rayleigh number reaches a critical value. With an appropriate Lyapunov function is proved that for the Rayleigh numbers below the critical value, the flow is globally stable. As the Rayleigh number gets higher and reaches a fixed value, a Hopf bifurcation occurs, and chaotic motion appears in the system. The critical and Hopf Rayleigh numbers relation are derived parametrically based on dynamical system theories. Also, numerical simulations will carry on the presented low-order model. Different dynamical behaviors of this flow and its transition from regular to chaotic motion are explained, with phase portraits and velocity-temperature diagrams obtained by numerical solutions. This parametric study can pave the way for future researchers to determine at around values of critical parameters should an experiment or direct numerical simulation be performed to have more accurate data without resorting to tests at all operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, a solitary wave propagation problem running up on a range of relatively steep slopes to gentle slopes is investigated. Boussinesq solitary wave generation method is used in five beach slopes with the still water heights of 15.0–68.6 cm and relative wave heights of 0.046–0.348. The incompressible smoothed particle hydrodynamics method is utilized as the numerical method. Simulation results are compared with analytical results and experimental data in terms of free surface displacement, maximum run up, shoreline movement and fluid particle velocity. Surface profile results agree reasonably with the analytical results at run down and horizontal particle velocities coincide with the experimental data. Furthermore, the results of maximum run up show that for moderate and large wave heights, Lagrangian numerical results pursuit the maximum run up of the experimental data with acceptable accuracy. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, attention is focused to clarify how temperature level may affect parallel mixing of two gas streams initially separated by a splitter plate. This is achieved by computing distinct cases with different inlet temperatures and comparing the corresponding results. A recently proposed kinetic model is utilized for the simulation of the flow field. The model provides a separate equation set for one component species of the system and an equation set for average quantities of the mixture. Thereby, it can automatically describe diffusion processes without the use of any coefficients for ordinary, pressure, and thermal diffusion which are generally required during Navier–Stokes computations of gas mixtures. [Copyright &y& Elsevier]

Determination of flow pattern within a tissue is a complicated and crucial task for several purposes including drug delivery and clinical treatments. However, as the vasculature composes of a complex network of interconnected vessels with a wide range of geometrical properties; even its realistic reconstruction is still challenging. Additionally, direct CFD simulation of a network of thousands of connected tubes with various configurations is a sophisticated process. In the present study, a novel approach is proposed to reconstruct the 3D vascular system using the angiography data. The network can be extended to reach any particular sizing level from main vessels to microvessels. Moreover, to determine the flow field throughout the vasculature, the CFD tool is utilized to generate a database of pressure and velocity distribution for a wide variety of branching scenarios. The obtained database is used as the training set of data by the GMDH algorithm to determine the connection between the input and output parameters. Finally, the combination of the trained GMDH algorithm and the reconstructed vasculature is incorporated to simulate the blood flow. According to the results, the proposed algorithm has an excellent capability to create the vascular system and predict the flow field within the tissue. [ABSTRACT FROM AUTHOR]

In this study, the inhalability of microparticles through a human nasal passage under various ambient airflow conditions is calculated. As megacities are becoming polluted and being exposed to the polluted windy outdoor environments is inevitable nowadays, from the toxicological point of view, it would be wise to investigate the impact of air pollution on human health. Though, as few studies have attempted to address this concern, especially for high free-stream velocities comprehensively, the main emphasis was placed on assessing the impact of both inhalation and Total Deposition Fraction (TDF) of particles. Several free stream airflow velocities from 1 to 70 km/h are simulated to cover almost all stormy outdoor conditions that could typically happen. RANS models and stochastic models for turbulent particle dispersion were examined to simulate the particle motions properly in such turbulent conditions. The impact of high ambient airflow velocities on the aspiration efficiency and the TDF of micro-particles were assessed for a wide range of particle sizes. The results reveal that TDF of the integrated airway is mostly higher than that of the detached airway system due to the non-uniformity of both airflow field and particle distribution which happens at the nostrils, similar to the work of Naseri et al. (Anderson and Anthony, 2013) [24]. Yet, contrary to that study in which the flow field was laminar, and there were no notable differences between the TDF of these two cases at different breathing flow rates, the differences become more notable when the breathing regime becomes fully turbulent. • Aspiration efficiency of large micro-particles decreases with increase in wind velocity. • Being exposed to windy conditions affects the deposition of micro-particles within the human extrathoracic airway system. • Total deposition of particles in the case of the integrated airway is mostly higher than that of the detached airway system. • CRW model predicts well the stochastic fluctuations. [ABSTRACT FROM AUTHOR]

• Partially liquefied vitreous was modeled as a two-phase Viscoelastic-Newtonian flow. • Two-phase solver was developed for linear and non-linear viscoelastic regimes. • An excellent agreements was found between experimental data and 3-mode Giesekus model. • Exact solution was derived for concentric cases of partial vitreous liquefaction. • The eccentric configurations can generate significant stresses and deformations. In this paper a numerical solver is developed in the OpenFOAM to capture the interface effects and dynamic characteristics of two-phase viscoelastic-Newtonian fluid flow for single and multi-mode viscoelastic models in linear and non-linear regimes. The code is based on finite volume method and the PIMPLE algorithm is used to couple the velocity and pressure terms. The dynamic mesh technique is used to model the movement of the computational domain and a modified classic volume-of-fluid approach is employed to capture the interface effects. In order to enhance the stability of the numerical procedure the discrete elastic split stress method is employed and introduced into the momentum equation. The present numerical model is validated in the linear regime by comparing the results with those of the analytical solution for which excellent agreement is observed. The main objective of this study is to investigate the effects of various angular frequencies, amplitudes and volume fractions on the flow dynamics of partial vitreous liquefaction in a two-dimensional model of the vitreous chamber subjected to sinusoidal motions. Concentric and eccentric configurations of the liquefaction are considered with the initial circular shape inside a cavity. Numerical results are obtained for the velocity field, shear stress, normal stress difference and streamline pattern and it is discussed how the partial vitreous liquefaction responds to the different oscillatory movements in comparison with a normal, healthy vitreous gel. It is observed that in concentric cases, the maximum values of shear stress and tangential velocity intensify by increasing angular frequency and their locations move from the wall into the domain of the cavity. In eccentric configurations significant interface deformations are observed. Moreover, the results indicate that the shear and normal stress values in the eccentric cases are higher compared to those in the concentric configurations. [ABSTRACT FROM AUTHOR]

Abstract Analyzing the airflow generated by a moving train in tunnels ventilated by jet fans is of significant importance because of the piston effects and the alternating pressure and velocity fields inside the tunnel. Moreover, high blockage ratio and train velocity in these tunnels have caused serious concerns about the impact of train-induced airflow on the performance of jet fans. This study aims at simulating the train movement in such tunnels and investigating the above-mentioned effects. To this purpose, a finite-volume numerical approach with dynamic mesh technique is used to perform several simulations of a large tunnel with eight rows of jet fans and different train velocities. The results demonstrate that for the case in which the train moves in the opposite direction of the jet fans' flow, their volume flow rates increase and decrease sharply, as the train head and tail reach the jet fans, respectively. However, the trend is opposite when the train travels along the direction of jet fans flow. From an electric perspective, it is shown that the generated flow field does not increase the motor torque and the current of the jet fans to a degree that causes the motors to shut down. Highlights • Maximum train velocity of 120 km/h and the tunnel blockage ratio of 0.16 were studied. • Jet fan flow rate changes sharply as the train head and tail reach that. • When the train moves in the opposite direction of the jet fan, flow rate increases first. • When the train travels along the direction of jet fans the trend is opposite. • The motor torque and the current of the jet fan is in the safe. [ABSTRACT FROM AUTHOR]

In the present study, six solitary wave generations by different mathematical approximations are investigated using a piston type wave maker at dimensionless amplitudes ranging from 0.1 to 0.6 and two water depths. Incompressible smoothed particle hydrodynamics is used to simulate solitary wave propagation along the fixed depth channel. The present numerical results are compared with analytical results and experimental data in terms of free surface displacements, fluid particle velocity, phase speed, paddle motion, etc. The present mesh-free numerical results of wave profile variations over time proved that “Rayleigh” has the lowest relative wave height variation. However, its solitary wave has notable phase lead, while “Third order” and “Ninth order” have the least wave lags. Furthermore, the record of present numerical free surface elevation at different distances and the loss of amplitude of the main pulse showed that regarding both of them, “Ninth order” has supremacy over five others. Considering the numerical velocity components of generated solitary wave, “Third order” and “Ninth order” trace analytical results more accurately than other four ones, whereas “Rayleigh” is the most accurate one in predicting the maximum runup. Finally, the paddle motion, its velocity, and displacement, as well as phase speed and outskirts decay coefficient are also compared and discussed intensely. [ABSTRACT FROM AUTHOR]

Abstract: Recently, several kinetic descriptions have been utilized for the simulation of gas mixture flows in microgeometries. Although such developments are important, Navier–Stokes computation can find extended use in engineering applications. In the present contribution, a rarefied flow of a gas mixture in the vicinity of a wall is concerned and new velocity-slip and temperature-jump boundary conditions are derived for the whole mixture. Appealing to these new boundary conditions, Navier–Stokes computation of microscale gas mixture flows becomes feasible. Consequently, the proposed conditions in conjunction with the Navier–Stokes equations and an equation for the conservation of species are solved for a He–Ne flow in a microchannel and suitability of the derived boundary conditions is demonstrated in the slip flow regime. [Copyright &y& Elsevier]

In this paper a new procedure for detection and quantification of the main features of ship models bubbly wake is presented. The method is based on light scattering characteristics of laser beams passing through the wake of ship models. An optical light scattering model is developed and validated in a series of steady bubbly flow tests in a water tank, with time-invariant mean multiphase flow properties. Then a series of unsteady tests are conducted in a towing tank so as to study bubbly wake properties of a transom stern model. Temporal wake strength and its final detection time and length are measured using light scattering measurements. Light scattering analysis provides longitudinal, lateral, and vertical distributions of the wake without any flow intrusion. Also by combining the experimental and analytical results, a complementary assay for determination of average bubble size and bubble number density distribution is presented. Effects of model velocity on the bubbly wake features of the transom stern are also investigated using the suggested procedures. Results indicate that increasing the model velocity increases the total bubbly wake length and lifetime. Details of the wake lateral distribution reveal the prominent contribution of transom stern diverging waves on the bubbly wake air entrainment. [ABSTRACT FROM AUTHOR]