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Safe operation of orbital platforms relies heavily on stability of fluid flows in microgravity, which are strongly affected by capillary forces. The paper considers multiphase fluid seepage through a porous medium. Questions of instability of the interface between liquids are discussed. The effect of capillary instability is shown, which was revealed during the processing of experimental data on the imbibition of a porous structure in microgravity conditions during parabolic flights. A mathematical model is proposed to describe the process of multiple imbibition of a porous medium under conditions of variable gravity. The model takes into account hysteresis, various models of capillary pressure are used during imbibition and drainage. The paper also considers a method for modeling the instability by transforming the constitutive equations. The method allows modeling additional blurring of the imbibition front. The results of modeling based on this method for capillary imbibition of a porous medium under microgravity conditions, as well as for the case when chemical interactions occur between flowing fluids, are considered. • The instability of the phase boundary during seepage is considered. • Flows are studied controlling safe operation of spacecraft fluid supply systems. • A new mathematical model for describing the multiple imbibition is proposed • The seepage with chemical interactions between the phases is considered. [ABSTRACT FROM AUTHOR]

In this paper, the flow of viscoelastic fluids is numerically studied through a planar gradual (non-abrupt) channel with the expansion ratio of 1:3. Here, the rheological model of the exponential Phan Thien–Tanner (EPTT) is used as the constitutive equation. For discretizing the governing equations, the finite volume method (FVM) employed on the collocated grid and the PISO algorithm is utilized for the velocity–pressure coupling. The main object of the current paper is to investigate the pressure drop and the energy losses of nonlinear viscoelastic flows in gradual expansions. For this purpose, the effects of expansion region and recirculation zones are examined on the pressure drop coefficient and the loss coefficient for different expansion angles and, Reynolds and Weissenberg numbers. The results show that at a constant expansion angle, the total pressure drop and total loss coefficients decrease with an increase in Reynolds or Weissenberg numbers. Moreover, the magnitude of the pressure drop and total loss coefficients increase, in an almost linear way, as the expansion angle increases between 10 ° to 70 ° . [ABSTRACT FROM AUTHOR]

This paper analyses two different configurations of horizontal axis Tidal Stream Turbines (TSTs) using a Blade Element Momentum Theory (BEMT) model. Initially, a ‘conventional’ three bladed and bare turbine is assessed, comparing against experimental measurements and existing literature. Excellent agreement is seen, increasing confidence in both the implementation of the theory and the applicability of the method. The focus of the paper lies on the analysis of a ducted and open centre turbine. An analytical adjustment to the BEMT model is applied, using empirical expressions detailed in the literature which are devised from Computational Fluid Dynamics (CFD) studies. This is modified to a symmetrical duct profile, calibrating certain geometrical parameters against blade resolved CFD studies of a bi-directional device. The results are validated with a coupled CFD blade element model (RANS BEM), where both models align very closely (within 2%) for most tip speed ratios (TSRs), including the peak power condition. Over predictions are seen at higher TSRs of up to 25% in power and 13% in thrust at TSR = 5, due to model limitations in replicating fully the complex flow interactions around the hub and the open centre. The presented approach benefits from significantly lower computational requirements, several orders of magnitude lower than reported in the RANS-BEM case, allowing practicable engineering assessments of turbine performance and reliability. [ABSTRACT FROM AUTHOR]

Analysis of transient fluid flow in porous media has several applications in geophysics/geotechnics and engineering. An in-depth evaluation of fluid flow behavior is critical in order to improve the understanding, and development of, laboratory measurement techniques in geo-mechanics, particularly permeability estimation. Given that considerable errors may be yielded in the derived permeabilities of sorptive rocks when using the conventional pressure-pulse decay method (PDM), this paper proposes a new experimental design, an optimized PDM, by creating dual pressure pulses to avoid the pressure disturbance due to compressive storage, ad-/de-sorption and thermal effect during the course of measurement. In this paper, the first of a two-part series, a mathematical model established for the conventional PDM was modified to closely represent the new experimental design, thereby extending the transient technique for permeability measurement of unconventional reservoir rocks, particularly ones with large sorption potential. Considering the complexity of analytical solutions of mathematical models, a comprehensive numerical investigation was established and a detailed comparison was carried out between the conventional and optimized PDMs. The results showed how the profiles of the decay curves change in space and time domain, and how pressure responses are influenced by various parameters in the experimental design for PDM. Combining the new design with numerical simulation results in an optimized technique for fast and accurate permeability measurement of sorptive rocks. In particular, Brace et al.’s solution, the most acknowledged and commonly-used permeability calculation method, was extended for permeability estimation of sorptive rocks. In Part 2, the experimental work under best-replicated in situ stress/strain conditions using the optimized method along with the numerical pressure response results obtained from computer simulation is presented. The results verified the practicality of the optimized PDM and the validity of Brace et al.’s solution for permeability measurement of sorptive rocks. [ABSTRACT FROM AUTHOR]

Highlights • Experimental investigation on flow through confined metal foam passage. • Investigating any possible effect of confined passage on flow characteristics. • Comparing RUC model to the experimental result. • Proposing correction in the RUC model based on experimental outcomes. Abstract This paper deals with flow behaviour through a confined passage filled with metal foams (MFs). Two sets (four samples) of aluminium foams of 20 and 40 ppi pore densities with 9–11% and 12–16% relative densities (RD) individually (as per supplier’s specification) were used for the study. Former RD belonged to uncompressed metal foams whereas the later was achieved by unidirectional compression of metal foam of 6–8% RD. Measured porosities of the uncompressed 20 and 40 ppi MF samples were equal, which was 0.88. However, measured porosities were 0.83 and 0.86 for compressed 20 and 40 ppi MF samples. Flow characteristics of both compressed and uncompressed samples were experimentally measured. Fourie-Plessis’s representative unit cell (RUC) model was used as an analytical tool for estimating pressure drop gradient through MFs because of its simplistic approach and independency from flow characteristics. Possible encasing wall effect on pressure drop was theoretically conducted. Due to a significant difference in estimated and experimentally obtained pressure drop gradient, authors have proposed a modification in the RUC model. The modified version of the RUC model was able to estimate pressure drop gradient of the uncompressed samples with a considerably higher accuracy. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for hydromechanical modelling of fractured rocks by linking a finite-discrete element solid model with a control volume-finite element fluid model based on an immersed-body approach. The adaptive meshing capability permits flow within/near fractures to be accurately captured by locally-refined mesh. The model is validated against analytical solutions for single-phase flow through a smooth/rough fracture and reported numerical solutions for multi-phase flow through intersecting fractures. Examples of modelling single- and multi-phase flows through fracture networks under in situ stresses are further presented, illustrating the important geomechanical effects on the hydrological behaviour of fractured porous media. [ABSTRACT FROM AUTHOR]

Abstract Most of the experience collected on wave overtopping is concentrated on emerged or zero-freeboard structures, and only few experiments are available on over-washed dikes. The experience on submerged crest conditions is principally related to rubble mound structures and limited to the wave reflection and transmission processes. The existing tools for the prediction of the average wave overtopping discharge (q) at dikes are therefore targeted to represent overtopped structures, leading to cautious estimates at over-washed dikes and unrealistic overestimations in case of catastrophic scenarios such as breached dikes. This paper proposes a new conceptual and practical method for the prediction of q that is valid for both over-washed and fully breached dikes. It consists of three physically-based formulae whose coefficients are fitted on a new numerical database of smooth structures under variable wave attack. The predictions are compared with the new numerical results and the data and the tools available from the literature, i.e. experimental data, formulae and neural network. The new method gives a more realistic representation of the overtopping and overflow processes, reducing significantly the overestimation in case of breaching and being at least as accurate as the existing tools in case of over-washing. Highlights • An innovative method is proposed for the estimation of wave overtopping and overflow discharge at dikes. • The method can be applied to over-washed and breached dikes. • The method is based on a coherent theoretical and physically-based framework. • The method consists of three equations for a practical application. [ABSTRACT FROM AUTHOR]

The accurate model of the jet-type valve, as the pilot control stage of a jet-pipe/deflector-jet servovalve, is of great significance to analyze and design a servovalve. However, the flow field in the jet-type valve is too complex to build an accurate mathematical model. In this paper, the collision between the liquid and the jet is supposed as the impact of jet on a moving piston, which makes a complex the fluid mechanical problem become simple. Based on this assumption, a model of the jet-type valve is developed in this paper. Unlike the previous models, the structural parameters, the distance between the jet-nozzle exit and receiving surface, the included angle between two receiver holes as well as the distance between two receiver holes, all can be considered in this model. To test and verify the theoretical model, the pressure and flow characteristic curves of a jet-type valve are given by the methods of flow filed numerical simulation and experiment.As shown by the verification results, the theoretical pressure characteristic curve is very approximate with the experimental data and numerical simulation, while the flow characteristic curves need to be modified and the modified model is valid. [ABSTRACT FROM AUTHOR]

We construct and analyze robust strong stability preserving IMplicit-EXplicit Runge-Kutta (IMEX RK) methods for models of flow with diffusion as they appear in astrophysics, and in many other fields where equations with similar structure arise. It turns out that besides the optimization of the region of absolute monotonicity, some other properties of the methods are crucial for the success of such simulations. In particular, the models in our focus dictate to also take into account the step size limits associated with dissipativity, positivity of the stiff parabolic terms which represent transport by diffusion, the uniform convergence with respect to different stiffness properties of those same terms, etc. Furthermore, in the literature, some other properties, like the inclusion of a part of the imaginary axis in the stability region, have been argued to be relevant. In this paper, we construct several new IMEX RK methods which differ from each other by taking various or even all of these constraints simultaneously into account. It is demonstrated for some simple examples as well as for the problem of double-diffusive convection, that the newly constructed schemes provide a significant computational advantage over other methods from the literature. Due to their accumulation of different stability properties, the optimized IMEX RK methods obtained in this paper are robust schemes that may also be useful for general models which involve the solution of advection-diffusion equations, or other transport equations with similar stability requirements. [ABSTRACT FROM AUTHOR]

Simulation and experimental verification of a fuel calibration system based on hydraulic metering cylinder has been carried out in this paper. A novel hydraulic metering cylinder is designed for more accurate flow rate measurement. The calibration workbench with this cylinder is presented and mathematically modeled. Also, the calibration system is numerically simulated in AMESim. The simulation results show that the calibration system can work smoothly. In addition, the impact of given plunger speeds and calibration strokes on the accuracy of the calibration results is experimentally verified. It can be found that stroke of approximate 600 mm and a medium given speed are the most effective ways to reduce the measuring error under the experimental condition provided in this paper. Moreover, a calibration error less than 0.5% is achieved in the fuel calibration system. [ABSTRACT FROM AUTHOR]

Despite the fact that the conventional one-dimensional model for counter-flow spray separation tower is advanced in reasonable accuracy as well as time and computational resources saving, it fails to describe the physical processes in details. In this paper, the concept of supersaturated state of the moist air was introduced, then a new sectional one-dimensional model was developed with a detailed derivation. A prototypic apparatus was set up and the reliability of the model was validated by the experimental study. When predicting the outlet solution temperature and outlet moist air wet bulb temperature, the relative errors would be more pronounced with a bigger heat and mass transfer driving potential, but they would not exceed 3.59% and 9.54% respectively under the experimental conditions. The simplifying assumptions, the ignored heat and mass transfer at cyclone region and the measuring errors are mainly blamed for the predicted errors. An in-depth heat and mass transfer investigation was conducted with the help of the validated model by studying the profiles of humidity ratio and moist air dry bulb temperature. The proposed model succeeded in capturing the state transformation of the air flow along the axis of the tower and the effects of the operating parameters on the process profiles are discussed. [ABSTRACT FROM AUTHOR]

The present paper aims to establish the MHD module of Anupravaha-1, a general purpose solver for fluid-flow, developed by our research group as a versatile computational tool for simulating MHD flows through complex geometric configurations. The code is capable of handling non-orthogonal, multi-block, structured grids and treats a coupled fluid–wall (conjugate) modeling to include thermal and electro-magnetic effects in the presence of duct walls and electro-thermally coupled manifolds. The solver module is thoroughly validated using various benchmark numerical and analytical results, which include, but not limited to the following variety of problems: (a) 2-D analytical and numerical reference cases of pressure driven flows in straight and curved channels, and natural convection in a rectangular enclosure, for Hartmann numbers Ha  ≤ 300. (b) Fully-developed flow through a rectangular duct for Hartmann numbers up to Ha  = 15,000, considering the duct walls to be all insulating (the Shercliff's case) and also with only the Hartmann walls partially conducting (Hunt's case II). (c) For the 3-D solver validation, comparative results for (1) the flow through a straight duct in the presence of a non-uniform magnetic field, (2) free convection in a cubical enclosure under a uniform magnetic field, and (3) an electro-magnetically driven flow in a toroidal duct for low Hartmann numbers ( Ha  ≤ 100), are obtained and discussed. (d) In addition, the implementation of a simple wall treatment method for computing high Hartmann number flows, as typically encountered in liquid metal cooled fusion-blanket applications, is tested using the case of flow through a rectangular duct in the presence of a homogeneous magnetic field for Ha  = 10,000–30,000. The performance of the code in the cases considered ranged from good to excellent. Lastly, comparison with the ALEX (Argonne Liquid metal EXperiment), for the case of flow through a rectangular duct in a fringing magnetic field is presented, that revealed the sensitivity of the results to the precise description of the magnetic field. [ABSTRACT FROM AUTHOR]

HyperVapotrons are highly robust and efficient heat exchangers able to transfer high heat fluxes of the order of 10–20 MW/m 2 . They employ the Vapotron effect, a complex two phase heat transfer mechanism, which is strongly linked to the hydrodynamic structures present in the coolant flow inside the devices. HyperVapotrons are currently tested in the Joined European Torus (JET) and the Mega Amp Spherical Tokamak (MAST) fusion experiments and are considered a strong candidate for the International Thermonuclear Experimental Reactor (ITER). The efficiency of heat transfer and the reliability of the components of a fusion power plant are important factors to ensure its longevity and economical sustainability. Optimisation of the heat transfer performance of these devices by the use of nanofluids is investigated in this paper. Nanofluids are advanced two phase coolants that exhibit heat transfer augmentation phenomena. A cold isothermal nanofluid flow is established inside two HyperVapotron models representing the geometries used at JET and MAST. A hybrid particle image velocimetry (PIV) method is employed to measure the flow and create a dense velocity vector map of a region of interest. The vector spatial resolution is 30 μm. The instantaneous and mean flow structures of a nanofluid are compared to those present during the use of a traditional coolant (water) in order to detect any departure from the hydrodynamic design operational regime of the device. It was discovered that the flow field of the JET model is considerably affected when using nanofluids, while the flow in the MAST geometry does not change significantly by the introduction of nanofluids. Evidence of a shear thinning mechanism is found inside the momentum boundary layer of the nanofluid flows and it might be important to calculating the pumping power losses of a functional nuclear fusion power plant cooling system ran with nanofluids instead of water. [ABSTRACT FROM AUTHOR]

A semi-implicit (non-)hydrostatic free-surface numerical model for two layer flows is derived from the Navier–Stokes equations by applying kinematic boundary conditions at moving interfaces and by decomposing the pressure into the hydrostatic and the hydrodynamic part. When the latter is ignored, the algorithm conveniently transforms into a solver for a hydrostatic flow. In addition, when the vertical grid spacing is larger than the layer depths, the algorithm naturally degenerates into a solver for the shallow water equations. In this paper, the presented numerical model is developed for the horizontal centrifugal casting, a metallurgical process, in which a liquid metal is poured into a horizontally rotating cylindrical mold. The centrifugal force pushes the liquid metal toward the mold wall resulting in a formation of a sleeve with a uniform thickness. The mold gradually extracts the sensible and the latent heat from the sleeve, which eventually becomes solid. Often a second layer of another material is introduced during the solidification of the first layer. The proposed free-surface model is therefore coupled with the heat advection-diffusion equation with a stiff latent heat source term representing the solidification. The numerical results show a good agreement with measurements of temperatures performed in the plant. A validation of the proposed model is also provided with the help of using other numerical techniques such as the approximate Riemann solver for the two layer shallow water equations and the volume of fluid method. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method (LBM) has been used in various fluid flow analyses as an alternative to the traditional method of computational fluid dynamics. In the study reported here, the LBM was used to simulate a simple Hele–Shaw melt flow of polymers considering their actual physical properties, whereas the Carreau fluid model was used to evaluate the polymer melt viscosity. Since the Reynolds number of a polymer melt flow is typically quite low due to its high viscosity, which in turn lowers its convergence rate in the LBM, introducing a new density offset method improved that rate. In this paper, cases of simulations with pressure or velocity inlet boundary conditions are discussed in which the density offset method is applied. [ABSTRACT FROM AUTHOR]

Flow resistance and enhanced heat transfer characteristics of TiO 2 -water nanofluids in a stainless-steel corrugated tube and a circular tube are investigated by experimental and numerical methods respectively. The flow and heat transfer characteristics of TiO 2 -water nanofluids and deionized water in test tubes are compared in this paper. In addition, effects of Reynolds number ( Re ) and nanoparticle mass fraction ( ω ) on flow and heat transfer performances are discussed respectively, and Nusselt number ( Nu ) and resistance coefficient ( f ) are studied respectively. Finally, comprehensive performance of flow resistance and heat transfer enhancement is evaluated. It can be obtained that adding nanoparticle into deionized water doesn’t cause a large additional resistance loss in some degree, while the combination of corrugated tube and TiO 2 -water nanofluids shows an excellent heat transfer enhancement, which can enhance the heat transfer by 53.95% at maximum extent. In addition, the corrugated tube has a strong sustainability in enhancing heat transfer. The enhanced heat transfer rising part (6000 ≤ Re ≤ 10,000) has a large rising slope (about 7.90E−5), and the descending slope (about 7.16E−6) of enhanced heat transfer part (10,000 ≤ Re ≤ 12,000) is small. [ABSTRACT FROM AUTHOR]

This paper reports the effect of changing the aspect ratio on the heat transfer and flow quantities over in-line tube banks. Two types of in-line arrangements were employed; square and non-square configurations. The models that were examined are a standard k-ε model, SST k-ω model, v2-f model, EB k-ε model and EB-RSM model. The closer results to the experimental data and LES were obtained by the EB k-ε and v2-f models. For the square pitch ratios, the solution has faced a gradual change from a strong asymmetric to asymmetric and then to a perfect symmetry. The strong asymmetric solution was found by the very narrow aspect ratio of 1.2. However, the behaviour of cases of 1.5 and 1.6 became less strong than that predicted in the case of 1.2. In the larger aspect ratio of 1.75, the flow behaviour is seen to be absolutely symmetric for all variables under consideration except Nusselt number. For the very large pitch ratio of 5, the flow has recorded maximum distributions for all parameters on the windward side of the central tube with a perfect symmetric solution around the angle of 180° while the vortex shedding frequency has recorded minimum value and the Strouhal number; therefore, has given the smallest value. However, for the non-square pitch ratio of constant transverse distance, the solution is still asymmetric for all parameters with merely one stagnation at the angle of 52° at the case of the 1.5 × 1.75 while by increasing the longitudinal distance to 2 and 5, the solution provided a comprehensive symmetry for all variables with two vortices are fully developed mirrored in shape on the leeward side of the central tube. On the contrary, for the non-square pitch ratio of constant longitudinal distance, the flow of the case of 1.75 × 1.5 provided two stagnation locations at around 52° and 308° with a very similar solution to the case square ratio of 1.75 for all variables whereas by increasing the transverse distance to 2 and 5, the solution recorded was not perfectly symmetric resulting in two different vortices and one stagnation position located at the leading edge of the cylinder provided by the case of 5 × 1.5. In terms of vortex shedding effect, the reduction in the Strouhal number at a constant transverse pitch is less steep than those at a constant longitudinal pitch. [ABSTRACT FROM AUTHOR]

This paper assesses the value of multi-scale near-surface (0∼5 cm) soil moisture observations to improve state-only or state-parameter estimation based on the ensemble Kalman filter (EnKF). To the best of our knowledge, studies on assimilating multi-scale soil moisture data into a distributed hydrological model with a series of detailed vertical soil moisture profiles are rare. Our analysis factors include spatial measurement scales, soil spatial heterogeneity, multi-scale data with contrasting information and systematic measurement errors. Results show that coarse-scale soil moisture data are also very useful for identifying finer-scale parameters and states given biased initial parameter fields, but it becomes increasingly difficult to recover the finer-scale spatial heterogeneity of soil property as the observation grids become coarser. In state-only estimation, near-surface soil moisture data result in improvement for shallow soil moisture profiles and degradation for deeper soil moisture profiles, with stronger influences from finer-scale data. With the decrease of background spatial heterogeneity of soil property, the value of coarse-scale data increases notably. Soil moisture data at two scales with contrasting information are found to be both useful. By updating spatially correlated soil hydraulic parameters, deviated observations still contain considerably useful information for finer-scale state-parameter estimation. Eventually, by presenting a difference information assimilation method based on EnKF we successfully extract useful information from soil moisture data containing systematic measurement errors. The current study can be extended to consider more complex atmosphere input and topography, etc. [ABSTRACT FROM AUTHOR]

The paper deals with the development of convective flows in a complex system of thin liquid layers occurring under the effect of thermal load. To study this process a mathematical model which is based on the decomposition of complex problem into unitary elements (modules) with some set of rules allowing their linkage with each other was constructed. Each module represents a monotypic local model. The fluid flow and heat transfer in each of these modules are described by the Navier-Stokes and thermal conductivity equations. The boundary conditions required to solve these systems of equations are represented explicitly and written in the form of conservation laws. The numerical analysis of effect of thermal load on the characteristics of the liquid layers movement depending on the Marangoni number is carried out. It is shown that physical and thermophysical properties of liquid layers play the decisive role. It is exactly they control the convective flows in layers and determine the position and shape of interfaces. The results of model problem solutions are presented. [ABSTRACT FROM AUTHOR]

The present paper presents fluid flow and mixed convective heat transfer characteristics past a semi-circular cylinder at incidence with a tandem square cylinder in cross flow. Using air ( Pr = 0.71 ) as an operating medium, numerical simulations are performed for the range of Reynolds numbers, 10 ≤ Re ≤ 45 and incidence angles, 0 0 ≤ α ≤ 180 0 . The effect of thermal buoyancy is brought about by varying the Richardson number in the range 0 ≤ R i ≤ 2 . The mathematical model is firstly validated with the experimental and numerical results from the literature and found to be in good agreement. The steady separated flow is observed to become unsteady periodic under the superimposed thermal buoyancy. Furthermore, apart from thermal buoyancy effect, angle of incidence is found to play a pivotal role in bringing hydrodynamic instabilities and thereby vortex shedding for such steady mixed convective flows. Functional dependence of drag ( C D ) , lift ( C L ) , and moment ( C M ) coefficients on the combined influence of α and R i , is explored and analysed in detail. Additionally, other global quantities, such as local and average Nusselt number distribution, Strouhal number ( S t ) are determined with respect to the various ranges of parameters considered in the present investigation. [ABSTRACT FROM AUTHOR]

An enhanced coupling strategy for the resolution of 6–degrees–of–freedom rigid body motion and unsteady incompressible fluid flow in Finite Volume collocated arrangement using PIMPLE algorithm and rigid mesh motion is presented in this paper. The improved coupling is achieved by calculating the 6–degrees–of–freedom motion equations after each pressure correction step in the pressure–velocity PISO (Pressure Implicit With Splitting of Operators) algorithm. Solving the 6–degrees–of–freedom equations after each solution of the pressure equation of the PISO loop accelerates the convergence, leading to smaller number of nonlinear pressure–velocity iterations needed per time–step. The novel approach is verified and validated on a heaving decay case, while the achieved acceleration in terms of the number of PISO loops is demonstrated on seakeeping simulations of a container ship. [ABSTRACT FROM AUTHOR]

Power law metachronal wave motion, responsible for the cilia transport is investigated in this paper using numerical tools. The dynamical analysis is made in channel and in tube to demonstrate the quantitative effect of the geometry. Similarity transformations are employed to convert the governing partial differential equations into a set of coupled ordinary differential equations. A swift and accurate collocation algorithm is applied to the boundary value problem (BVP) of coupled ordinary differential equations. A nondimensional graphical analysis of the waving amplitude is reported by varying the flow consistency and flow behavior indices. [ABSTRACT FROM AUTHOR]

In this paper, the problem of a steady laminar three-dimensional stagnation point boundary layer flow (Homann stagnation flow) on a permeable moving surface with anisotropic slip in a viscous fluid is investigated. A similarity transformation reduces the governing system of nonlinear partial differential equations into the ordinary (similarity) differential equations. The resulting equations are then solved numerically by using the bvp4c function in Matlab. The effects of surface mass transfer parameter, slip parameter and moving parameter on the fluid flow characteristics are presented in the forms of tables and figures and are discussed in detail. Finally, it is concluded from the stability analysis that the first (upper branch) solution is stable and physically realizable, while the second (lower branch) solution is not stable. [ABSTRACT FROM AUTHOR]

Floods resulting from extreme events like tsunamis may inundate widespread inland areas, but vegetation can act as a natural buffer zone to reduce the inundation area and dissipate the energy of flowing water. This paper summarizes a series of laboratory experiments in which the energy loss through emergent vegetation in a steady subcritical flow was investigated. The energy loss was determined against vegetation of variable thickness ( dn , where d = diameter of cylinder, n = number of cylinders in a stream-wise direction per unit of cross-stream width), density ( G/d , where G = spacing of each cylinder in cross-stream direction, d = diameter of cylinder), and initial Froude number. On the upstream side of vegetation, the backwater rise increased by increasing both vegetation thickness and density. Contrarily, on the downstream side a breaking undular jump with a lateral shock wave was observed for a dense vegetation arrangement ( G/d = 0.25), whereas a non-breaking undular jump with and without air bubbles was identified for intermediate ( G/d = 1.09) and sparse ( G/d = 2.13) vegetation conditions, respectively. Under these conditions, the maximum energy reduction due to a jump reached 6.4% for dense vegetation, and was reduced to 1.7% and 1.4% for intermediate and sparse vegetations, respectively. Hence, denser vegetation offers larger resistance, thus causes significant energy loss. [ABSTRACT FROM AUTHOR]

A study is reported that examines computations of turbulent particle agglomeration with one-way and two-way phase coupling for cases with small overall particle concentration. The fluid flow was computed using a direct numerical computation using the point-force approximation for particle-induced body force, and a soft-sphere, adhesive discrete-element method was used to simulate the particulate transport and agglomerate formation. Computations were performed with different values of the Stokes number and the adhesion parameter. A variety of measures were used to examine both the effect of particle agglomeration on the fluid turbulence and the structure and flow field within the particle agglomerates. It was found that agglomeration has little influence on the attenuation of turbulence by the particles, at least in the range of Stokes numbers examined in the paper. Computations with two-way coupling generated agglomerates that were larger and contained more particles than those for one-way coupling. The agglomerate structure for both one-way and two-way coupling cases had a fractal structure with a similar value of the fractal dimension. As the agglomerate size increased, the fluid motion inside the agglomerates was found to become increasingly correlated to the agglomerate velocity, acting to decrease the relative velocity and shear stress of the inner particles within the agglomerate. [ABSTRACT FROM AUTHOR]

The present work aims to conduct CFD simulations of different types of fluidized beds with the same simulation setup. For this, a suitable validation experiment from literature must be identified that mimics the different states of fluidization that are of interest. The paper discusses which requirements need to be fulfilled by such a validation experiment. Different dimensionless groups need to be matched between the actual system under investigation (lab-scale gasifier) and the validation experiment from literature. This is shown using a flow regime map. The experiment is intended to provide several hydrodynamic measurements such as pressure drop, pressure drop fluctuation, voidage and velocity profiles. After a suitable reference experiment is identified from a literature review, Euler-Euler simulations are conducted to reproduce the experimental series. The applied set of models and parameters are based on the kinetic theory of granular flow. The required grid resolution and physical simulation time for averaging are carefully discussed. The numerical simulations show good agreement with the experimental results found in literature. A critical discussion about the potential limitations of the experimental setup in terms of proper gas distribution is conducted together with a discussion of the limits of the selected modeling approach. Finally, the validated simulation setup is applied to a multi-zone lab-scale gasifier. The simulation results show very good agreement with the proposed hydrodynamics in the different zones of the gasifier. [ABSTRACT FROM AUTHOR]

This paper deals with the numerical investigation of heat transfer by mixed convection inside ventilated cavities with supply and exhaust slots, and filled with air under a steady and turbulent flow regime. Four configurations, rated A, B, C and D are considered here, according to the position of the inlet and outlet air ports: A, the inlet is on the top of the left vertical wall, while the outlet is on the bottom of the right vertical wall; B, the inlet is on the bottom of the left vertical wall and the outlet at the top of the opposite wall; C, the two slots are on the same side, i.e. the inlet is at the bottom and the outlet at the top of the left vertical wall, and D, the inlet is at the top and the outlet at the bottom of the left vertical wall. The bottom of the cavity is kept at a temperature T H and other walls are fixed at a temperature T C , with T H > T C . The cavity is provided with two slots: an inlet slot for introducing fresh air, and an outlet slot to extract hot air. The main aim sought here is to analyze the ventilation efficiency for temperature distribution, and fix the best configuration providing the thermal comfort targeted. We also address the influence of heating on the behavior of flow and thermal comfort, while considering different Rayleigh numbers ranging from 6.4 × 10 8 to 3.2 × 10 9 . Numerical studies have been yet devoted to these configurations, using RANS simulations. The RNG k-ε turbulence model has been adopted for the turbulence closure, and the set of governing equations was then numerically solved via the finite volume method. The SIMPLEC algorithm was associated to ensure the pressure-velocity coupling. In terms of results achieved, the configuration D provides a better ventilation effectiveness for temperature distribution ε T and ensures an even temperature in the occupied zone. As for configurations A and C, they maintain an acceptable level of heat and can be used in winter period to ensure good indoor air quality, while configuration B provides an efficiency close to unity and can be used to insure indoor air quality in temperate climate zones. [ABSTRACT FROM AUTHOR]

This paper deals with the flow of solid/liquid mixtures through long-distance pipelines. Such flows can be destabilized by the formation of local plugs which may impede or even block the flow. Plugs may develop at the interface between regions of different mean concentration. The driving force for the development of such plugs is the existence of local gradients of the axial flux of solids. A mathematical model is developed which describes this mode of plug formation in slurry pipelines. Several assumptions and approximations enable us to reduce the 3D continuity equation of the solid particles to an effective 1D-equation that contains a concentration-dependent flux function. The latter equation is solved numerically. Illustrative calculations lead to the conclusion that the accumulation of material in a plug does not continue without limit but instead levels off at values that are pumpable under most practical conditions, provided that a certain margin of overdesign is in place. [ABSTRACT FROM AUTHOR]

There are many core flooding studies showing that the liquid-measured permeability is lower than the Klinkenberg-corrected gas permeability. The flow velocity in a low pressure gradient regime is lower than what is estimated from Darcy’s law. This phenomenon is considered as low-velocity non-Darcy flow in the literature. Besides, many researchers believe that there is a threshold pressure gradient (TPG) that needs to be overcome before the fluid flow can occur. The related results in the literature are critically reviewed in this paper. By analyzing the flow mechanism, considering boundary effect, and presenting counter examples, we conclude that the low-velocity non-Darcy flow regime consists of a nonlinear flow part and a linear flow part. The nonlinear flow part starts from the zero pressure gradient instead of TPG. Based on this observation, a non-Darcy model is introduced and the corresponding correlation parameters are derived by fitting the available experimental data. This model is used to estimate the well performance of a vertical well and a multi-fractured horizontal well. For a vertical well, the production rate of non-Darcy flow is much smaller than that of Darcy flow, and the ultimate oil recovery of non-Darcy flow is approximately 48% of the Darcy flow. The production rate of a multi-fractured horizontal well if non-Darcy flow is considered is smaller in the beginning but greater than the corresponding Darcy flow rate after about some time (in our example model, 2700 days). The ultimate recovery factor of non-Darcy flow is 80% of Darcy flow, which indicates that multi-fractured wells are less affected by the low-velocity non-Darcy phenomenon compared with the vertical wells. Multi-fractured horizontal wells exhibit a significant advantage in developing shale and tight reservoirs, and low velocity non-Darcy flow plays a significant impact on the well production performance in tight and shale reservoirs. [ABSTRACT FROM AUTHOR]

Scaling-up of filtration systems in the pharmaceutical industry to provide the correct filtration capacity is a complex process. When several filters are used in parallel, the pressure and flow distribution within the system can be modeled using well-established constitutive laws to a high degree of accuracy, as shown in this paper. By combining the model with experimental fouling data, it is also possible to accurately predict the flow and pressure distribution during an entire filtration run. A process is discussed that uses this model to determine how the capacity of a filtration system can be accurately predicted using a minimal set of measurements. [ABSTRACT FROM AUTHOR]

In this paper, we present an efficient adaptive mesh method for solving phase-field model of a mixture of two-phase incompressible fluid flows. The adaptive mesh is generated by a coordinate transformation that is determined as the solution of the classical problem of the optimal mass transportation, also known as Monge–Kantorovich problem (MKP). The numerical solution of the MKP is computed by taking the gradient of the steady state solution of a parabolic Monge–Ampère equation (PMAE). Several numerical experiments are conducted to demonstrate the performance of the PMAE method for solving phase-field models. The numerical results illustrate that the adaptive mesh computed with PMAE method captures well the moving interface of the phase-field function. [ABSTRACT FROM AUTHOR]

This paper presents a new step-wise sequential solution strategy for the synthesis of heat integrated water networks (HIWNs) comprising of two mathematical models. The first model minimizes water and energy costs. The optimal freshwater and water flow rates within the HIWN are determined from this model. Using these optimal flow rates, different configurations of HIWN are evaluated for the purpose of heat integration. The second model is the stage-wise heat exchanger network (Yee and Grossmann, 1990), which is solved for each of the evaluated network configuration in a sequential manner. Using this proposed strategy, a set of locally optimal HIWNs are produced and the best one is chosen based on the minimum total annual cost (TAC). The proposed sequential strategy is applied to small and medium sized examples in the literature. The results show that the proposed new sequential solution strategy can be successfully applied to small and medium sized HIWN problems. [ABSTRACT FROM AUTHOR]

This paper suggests hyperbolic relaxation system as a new efficient way in finding various types of numerical solutions of forced Korteweg–de Vries (fKdV) equations. When non-periodic numerical solutions such as hydraulic falls of fKdV equations with bumps are considered, the application of the spectral method or the finite difference methods may not work properly. As an alternative, the relaxation method has been applied to obtain the hyperbolic system for fKdV equations. The computational results show that the derived relaxation systems capture both hydraulic falls and solitary-type solutions accurately without numerical oscillations and require much less computational costs than other methods. [ABSTRACT FROM AUTHOR]

The micropiled raft (MPR) offers an efficient foundation system that combines the advantages of micropiles and piled rafts that can be used as primary foundation system or to enhance an existing raft foundation. In this paper, a calibrated and verified finite element model (FEM) with centrifuge tests was used to carry out a numerical investigation on the performance of MPR in sand. A total of 78 different cases were analyzed in this study to assess the behavior of MPR in sand taking into account a number of factors that may influence its behavior such as: the number of micropiles (MPs), the spacing to micropile diameter ( S / D mp ), the raft thickness, type of loading and soil density. The outcomes of this investigation should help in understanding the effect of these factors on the MPR axial stiffness, including; differential settlement; load sharing between the MPs and the raft; and the raft bending moment. Moreover, the ability of the PDR method to evaluate the axial stiffness of a MPR for the preliminary design stage is examined. It was found that the MPR system has the ability to increase the tolerable bearing pressure by 190% compared to an isolated raft system. In addition, an adjustment factor ( ω PR ) for PDR method was introduced to account for the raft flexibility. [ABSTRACT FROM AUTHOR]

In the last decades numerous coal mines have been closed. One way to overtake the costs associated to the mine closure is the geothermal use of the water stored in the closed and flooded mine workings. The temperature of the water flooding from the mine voids, in some cases reaching depths of several hundreds of meters, is suitable for space heating and cooling by means of the use of ground source (geothermal) heat pumps (low-enthalpy geothermal systems). Flooded mine voids constitute new-created pseudokarstic aquifers or reservoirs, which can store significant volumes of groundwater. However, the recharge and the heat capacity of these systems are finite, and this is the main concern when using mine water as a heat source or sink. These reservoirs can be regulated by means of flow extraction and injection depending on the use demands; notwithstanding, these flows have to be limited to a sustainable value, in order to avoid the exhaustion of the capacity of the aquifer to provide or store heat. Several numerical and analytical models have been created with this aim, with the shortage of hydrogeological and thermal data as main drawback. A literature review of the existent flow and heat transfer models applied to geothermal use of mine water has been undertaken, both analytical and numerical models are considered. The main parameters that have influence in the flow and heat exchange processes, have been analysed. The present paper can be used as basic guidelines to aid when selecting a modelling method for a specific scenario. [ABSTRACT FROM AUTHOR]

The present paper deals with a turbulent dual jet consisting of a wall jet and an offset jet. The flow field has been numerically simulated using two-dimensional unsteady RANS equations. The Reynolds number based on the separation distance between the two jets ( s ) is R e = 10 , 000 . The width of the offset jet nozzle equals the separation distance between the two jets. To examine the influence of the bottom wall, the width of the wall jet nozzle ( h ) has been varied in a range 0.2 ≤ h / s ≤ 2 . According to the computational results, for h / s = 0.2 , the flow field remains to be always steady with two counter-rotating stable vortices in between the two jets. On the contrary, within the range of 0.3 ≤ h / s ≤ 1 , the near flow field demonstrates a periodic vortex shedding phenomenon similar to what would be observed in the near wake region for flow over a two-dimensional bluff body. Within this flow regime, the Strouhal number based on the vortex shedding frequency gradually decreases with the progressive increase in h / s . However, for h / s > 1 , although the periodic vortex shedding phenomenon is still evident in the flow field, the Strouhal number becomes insensitive to the bottom wall similar to the flow behaviour for a flow over an unconfined cylinder. [ABSTRACT FROM AUTHOR]

Numerical simulation of separated flows in rocket nozzles is challenging because existing turbulence models are unable to predict it correctly. This paper addresses this issue with the Spalart–Allmaras and Shear Stress Transport (SST) eddy-viscosity models, which predict flow separation with moderate success. Their performances have been compared against experimental data for a conical and two contoured subscale nozzles. It is found that they fail to predict the separation location correctly, exhibiting sensitivity to the nozzle pressure ratio (NPR) and nozzle type. A careful assessment indicated how the model had to be tuned for better, consistent prediction. It is learnt that SST model's failure is caused by limiting of the shear stress inside boundary layer according to Bradshaw's assumption, and by over-prediction of jet spreading rate. Accordingly, SST's coefficients were empirically modified to match the experimental wall pressure data. Results confirm that accurate RANS prediction of separation depends on the correct capture of the jet spreading rate, and that it is feasible over a wide range of NPRs by modified values of the diffusion coefficients in the turbulence model. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model and corresponding numerical results for a power-law fluid flowing in a channel partially filled with a homogeneous and isotropic porous medium. At the interface between the clear fluid and the porous material, a model for the stress jump condition takes into consideration the behavior of a power-law fluid. This study shows that the use of a modified permeability, K * , satisfactorily describes the friction factor of the flow for Re η ∗ ≤ 1 (Darcy regime). The mathematical modeling presented, supported by comparisons with analytical and numerical results, also shows that the form drag must be taken into account in the momentum equation, even for a power-law fluid. The mathematical modeling presented has been used to simulate Newtonian as well as power-law fluids flowing in both porous and unobstructed media. For a channel partially filled with porous material and under a fixed mass flow rate, results indicated that the pressure drop is a function of porosity, Darcy number, shear jump coefficient, β , and flow behavior index, n . [ABSTRACT FROM AUTHOR]

In this paper, we define a certain proportional volume property for a unit vector field on a spherical domain in S 3 . We prove that the volume of these vector fields has an absolute minimum, and that this value is equal to the volume of the Hopf vector field. Some examples of such vector fields are given. We also study the minimum energy of solenoidal vector fields which coincides with a Hopf flow along the boundary of a spherical domain of S 2 k + 1 . [ABSTRACT FROM AUTHOR]

Since the Vreman subgrid-scale model was proposed, different types of flow fields have been used to research the applicability of this model. However, the applicability of the model to a flashover heat flow field simulation and the optimal model coefficient for room fires have not been reported. In this paper, the flashover room fire experiments of different opening sizes (ventilation factor) are conducted in an experimental room of size similar to ISO9705, and the room temperature at typical locations is measured. On the same numerical simulation platform, the room temperature field is simulated numerically using the large eddy simulation based on the Vreman and Smagorinsky subgrid-scale models. When the ventilation factors are 1.932 and 2.178, a Vreman subgrid coefficient of 0.02–0.04 is more applicable to the simulation of the temperature field. Overall, the simulation results of the maximum temperature based on the Vreman subgrid-scale model are slightly better than that of Smagorinsky subgrid-scale model. Moreover, the simulation result of the temperature change according to the time from the Vreman subgrid-scale model is similar to the experimental result. However, near the corner of the door in the room, the numerical simulation results underestimate the maximum flow field temperature in the room’s upper part. When the Vreman subgrid-scale model simulates the temperature field in the room with a subgrid coefficient of 0.04 and a ventilation factor of 2.263, the simulation results are better than the results from the Smagorinsky subgrid-scale model with a subgrid coefficient of 0.2. However, when the ventilation factor is 1.397 and the opening is relatively small, the large eddy simulation result based on the Vreman subgrid-scale model with a subgrid coefficient of 0.04 is worse than the results based on the Smagorinsky subgrid-scale model with a subgrid coefficient of 0.2. [ABSTRACT FROM AUTHOR]

The paper is focuses on the numerical simulation and analysis of coupled heat and mass transfer under ice formation conditions in the cross-flow plate heat exchanger. The simulation is performed using the original mathematical model. The presented model was validated against experimental data. The obtained results showed satisfactory agreement with the data obtained from the experimental measurements. Numerical simulation reveals many unique features of considered heat exchanger connected with the heat and mass transfer occurring in the return air channel under ice formation conditions. The results of computer simulation showed that the efficiency gains are sensitive to various inlet conditions, and allow for estimation of the safe operating conditions for different inlet return airflow parameters, based not only on the exhaust air temperature but also on its relative humidity and different thermal efficiency of the exchanger. Several goals were achieved, including: establishing the most unfavorable operating conditions (from the standpoint of ice formation on the plate surface of the return air channels) for cross-flow plate heat exchanger, which correspond to the inlet value of the return airflow dew point temperature equaled to 0 °C, impact of the ice formation on temperature effectiveness, impact of inlet relative humidity on temperature effectiveness and safe operating conditions and safe operating conditions for variety of inlet exhaust air parameters. [ABSTRACT FROM AUTHOR]

This paper presents an advanced mathematical model of a thermoelectric generator that includes the effect of the temperature gradient in the flow direction. The parameters of the exhaust gas from an engine may fluctuate during engine operation; thus, the influence of this fluctuation in the exhaust gas parameters on the optimal thermoelectric performance was considered with the objective of maximizing the total power output through the aid of Fortran. The optimum module areas corresponding to the maximum power output were found to be greatly affected by the flow rate of the exhaust gas but not by the gas temperature. The effect of the fluctuation in exhaust gas parameters on the performance of the corresponding thermoelectric generator at the maximum power output was also studied. A power deviation analysis method was introduced in order to design the optimal TEG module area for a high power output. Based on the results, the optimal design areas were 0.22 m 2 for the co-flow and 0.3 m 2 for the counterflow. The counterflow arrangement is recommended because it maintains a smaller deviation from the peak power output than a co-flow arrangement at their respective optimal design areas if there is sufficient system space. [ABSTRACT FROM AUTHOR]

This paper presents in-depth analyses of four stress integration algorithms for finite deformation elastic–plastic constitutive relations. In particular, the four integration schemes were developed for both non-Associated Flow Rule (non-AFR) and Associated Flow Rule (AFR) in the continuum level of plasticity theory. The four integration schemes are (1) fully implicit backward Euler, (2) semi explicit convex cutting plane, (3) fully explicit classical forward Euler and (4) fully explicit forward Euler named Next Increment Corrects Error (NICE-1), which were implemented into the user material subroutines of finite element software ABAQUS. Analysis on numerical accuracy was carried out by using uniaxial tensile simulations at various orientations and time increments. The same analysis was also conducted for uniaxial tension/compression tests to investigate the effect of time increment on the calculated hardening curve. Finally, cylindrical cup deep drawing (manufacturing process which stamps a cylindrical cup) simulations were performed to compare computation time and accuracy for both AFR and non-AFR schemes for the evaluation of more realistic forming application. From the systematic comparative analyses, the following conclusions are made; (1) Caution should be exercised when finding an optimum time increment for explicit integration schemes. (2) The computation time and accuracy for both AFR and non-AFR are not much different when identical integration scheme is used. (3) For the simulation of large scale sheet metal forming applications, the explicit type stress integration algorithm can be a more practical choice considering that it does not deteriorate the computational accuracy and efficiency compared to the fully implicit algorithm. [ABSTRACT FROM AUTHOR]

Internal bone remodeling subjected to coupled axial force and radial loading is studied in this paper. A theoretical model is developed based on a novel stimulus function expressed in terms of a relation between radial strain applied to the pericellular matrix and the interstitial fluid velocity in the lacunar-canalicular system. An assumption of homogeneity is made in order to obtain a continuum representation. Theoretical results are presented to verify the proposed remodeling theory. [ABSTRACT FROM AUTHOR]

This paper concerns heat exchange devices with a zigzag configuration containing multi-phase change materials (m-PCMs). A two dimensional mathematical model was established to model the charging behaviour. An experimental system was built to validate the model. The modelling results agree reasonably well with the experimental data for a single PCM, establishing confidence in the model. Extensive modelling was then carried out under different conditions. The results show that the use of m-PCMs intensifies the charging process in comparison with the use of a single PCM. Given other conditions, a larger phase change temperature difference between the m-PCMs gives a more remarkable enhancement of the charging process, and the use of m-PCMs with an unequal mass ratio gives further intensification. The modelling results also show that, for a given input power, an optimal fluid velocity exists for obtaining a high rate of the melting process. [ABSTRACT FROM AUTHOR]

It is important to study the falling-film pattern of a horizontal tube bundle in order to set up a heat and mass transfer model accurately. The falling-film pattern of a horizontal tube bundle is simulated in this paper. The technique is based on computational flow dynamics (CFD) for the two-phase flow of gas and water. The experimental results were used to validate the mathematical model. It indicates that the simulation results accord with experimental data well. The simulated results show that the flow pattern varies with different flow rates. Under the different flow rates, it observes the droplet, droplet-columnar, columnar, columnar-sheet and sheet flow patterns. The critical value is 0.0125 kg/s between droplet and columnar, and the critical value is 0.02 kg/s between columnar and sheet. [ABSTRACT FROM AUTHOR]

Abstract: An application of group analysis provides a regular procedure for mathematical modeling by classifying differential equations with respect to arbitrary elements. This paper presents the group classification of one-dimensional equations of fluids where the internal energy is a function of the density, the gradient of the density and the entropy. The group classification separates all models into 83 different classes according to the admitted Lie group. Some invariant solutions are studied. [Copyright &y& Elsevier]

Abstract: This paper presents a stabilized finite element formulation of the hydrodynamic Boltzmann transport equation (HBTE) to predict nearly incompressible fluid flow. The HBTE is discretized with Hermite polynomials in the velocity variable, and a streamline upwind Petrov–Galerkin formulation is used to discretize the spatial variable. A nonlinear stabilization scheme is presented, from which a simple linear stabilization scheme is constructed. In contrast to the Navier–Stokes (NS) equations, the HBTE is a first order equation and allows for conveniently enforcing Dirichlet conditions along immersed boundaries. A simple and efficient formulation for enforcing Dirichlet boundary conditions is presented and its accuracy is studied for immersed boundaries captured by the extended finite element method (XFEM). Numerical experiments indicate that both the linear and non-linear stabilization methods are sufficiently accurate and stable, but the linear formulation reduces the computational cost significantly. The accuracy of enforcing boundary conditions is satisfactory and shows second order convergence as the mesh is refined. Augmenting the boundary condition formulation with a penalty term increases the accuracy of enforcing the boundary condition constraints, but may degrade the accuracy of the global solution. Comparisons with results of a single relaxation time lattice Boltzmann method show that the proposed finite element method features greater robustness and lesser dependence of the computational costs on the level of mesh refinement. [Copyright &y& Elsevier]