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Artificial upwelling by the use of airlift pump is regarded as an effective way in utilizing deep ocean water and actualizing ocean fertilization. This paper focuses on numerical analysis of steady air–water two-phase flow in a vertical pipe of an airlift system based on one-dimensional multi-fluid model. The depth distributions of 6 physical quantities such as volumetric fractions and axial velocities of two phases, air density and pressure are calculated by solving the governing equations or by integrating the vector form of nonhomogeneous ordinary differential equation for two-phase flow interval. Upon successful verification of the present numerical model through a comparison with precedent theoretical and experimental results in case of a vertical pipe with length of 7.86 m, the model is extended to the case of artificial upwelling from water depth of 2000 m. The effects of submerged depth of air–water mixer on the pumped amount of water and the depth distributions of 6 physical quantities are considered. • This paper is concerned with numerical analysis of steady air–water two-phase flow in a vertical pipe of an airlift system to lift deep ocean water. • The depth distributions of 6 physical quantities such as volumetric fractions and axial velocities of two phases, air density and pressure are obtained from one-dimensional multi-fluid model. • The present model can be applied to predict the performance of airlift pump for lifting deep ocean water and the depth distributions of 6 physical quantities in axial direction. [ABSTRACT FROM AUTHOR]

This paper presents a new immersed boundary method for rigid particles of arbitrary shape and arbitrary density, which can be exactly zero. Especially in the latter case, the coupling of the fluid and the solid part requires special numerical techniques to obtain stability. Exploiting the direct forcing approach an algorithm with strong coupling between fluid and particles is developed, which is exempt from any global iteration between the fluid part and the solid part within a single time step. Starting point is a previously proposed method restricted to spherical particles [37]. It is proved that the coupling concept can be generalized to rigid particles with complex shapes, which is not obvious a priori . The extension requires various non-trivial methodological extensions, especially with respect to the angular motion of the particle. Using analytical techniques it is demonstrated that the implicit treatment of the coupling force in the equations of motion results in additional terms related to a surrounding numerical fluid layer. As a main improvement over other non-iterative methods the proposed scheme is unconditionally stable for the entire range of density ratios and particle shapes allowing large time steps, with Courant numbers around unity. To date, no other non-iterative coupling approach offers such a generality regarding fluid-particle interactions. In addition to the detailed description of the underlying methodology and its differences from other methods, the paper provides all modifications required to improve immersed boundary methods for particulate flows from weak to strong coupling. Furthermore, an extensive validation of the scheme for particles of different density ratios and shapes is presented. The accuracy of the method as well as the convergence behavior are assessed by systematic studies. [ABSTRACT FROM AUTHOR]

The paper deals with the construction and analysis of efficient high order finite volume shock capturing schemes for the numerical solution of hyperbolic systems with stiff relaxation. In standard high order finite volume schemes it is difficult to treat the average of the source implicitly, since the computation of such average couples neighboring cells, making implicit schemes extremely expensive. The main novelty of the paper is that the average of the source is split into the sum of the source evaluated at the cell average plus a correction term. The first term is treated implicitly, while the small correction is treated explicitly, using IMEX-Runge–Kutta methods, thus resulting in a very effective semi-implicit scheme. This approach allows the construction of effective high order schemes in space and time. An asymptotic analysis is performed for small values of the relaxation parameter, giving an indication on the structure of the IMEX schemes that have to be adopted for time discretization. Several numerical tests confirm the accuracy and efficiency of the approach. [ABSTRACT FROM AUTHOR]

This paper reports on the adaptation of a Lattice Boltzmann based free surface flow solver to the simulation of complex fluid-ship-ice interactions in marine engineering. The analysis is restricted to the interaction of already broken ice floes and the ship hull, aiming at the optimization of a ship hull’s capability to clear the ice and keep it away from the propulsion device. The ice floes and the ship hull are treated as rigid bodies. In order to model the dynamics of the colliding rigid multi-body systems, a coupling of the flow solver to the Open Dynamics Engine (ODE) is established. The basic methodology and initial validation of the fluid-structure coupling is presented. Then, basic validations of the employed collision and friction models are given, particularly focusing on interacting surface triangle meshes that later serve to describe the ice floes. Finally, a three-dimensional validation case shows that the ship-fluid-rigid-ice interaction forces agree well with available reference data. Apart from the numerical coupling, performance has to be addressed. The employed flow solver elbe uses graphics processing units (GPUs) to accelerate the numerical calculations. In order to make the GPU performance accessible to colliding multi-body systems, a careful and tailor-made implementation is presented in the paper. The resulting optimized elbe -ODE solver allows for the investigation of three-dimensional fluid-ship-ice interactions in a very competitive computational time, on off-the-shelf desktop hardware. [ABSTRACT FROM AUTHOR]

This paper examines the effect of modelling choices on the numerical simulation of premixed methane/air combustion in narrow channels. Knowledge on standard and well-accepted numerical methods in literature are collected in a cohesive document. The less well-established modelling choices have been thoroughly evaluated and discussed. A systematic method of computing the grid convergence index (GCI) has been presented for refining the computational grid. Two types of inflow boundary conditions have been tested and compared in terms of their wave-damping characteristics. The effect of different reaction schemes on simulation results have been examined and an appropriate mechanism (DRM-19) has been selected. Various types of ignition strategies to initiate the flame have been tested and compared. The transient ignition process which has not been discussed extensively in existing literature has been quantitatively described in this paper. [ABSTRACT FROM AUTHOR]

Highlights • Seventh order finite volume compact-WENO scheme is proposed for solving 1D and 2D hyperbolic conservation laws. • The parametrized maximum principle preserving and the parametrized positivity satisfying flux limiter flux limiter is coupled with the scheme. • The one dimensional HLLC flux function is used to compute the interface fluxes. • High-resolution properties with compact stencil. Abstract In this paper, we construct a new seventh-order finite volume compact weighted essentially non-oscillatory (WENO) scheme for solving one and two dimensional hyperbolic conservation laws. We extend the main idea of fifth-order finite volume compact-WENO scheme which comes from the original WENO schemes to construct the present seventh-order scheme, where fourth-order compact stencils will be combined with nonlinear weights to get seventh-order finite volume compact-WENO scheme. The parametrized maximum principle preserving flux limiter is coupled with the seventh-order compact-WENO scheme for solving scalar hyperbolic conservation laws and the parametrized positivity satisfying flux limiter is applied to the new scheme for solving compressible Euler equations to maintain positive density and pressure. The HLLC (Harten, Lax and van Leer) flux function is used to compute the interface fluxes in the finite volume formulation. A number of 1D and 2D numerical tests are performed to demonstrate the efficiency and high-resolution properties of the proposed high-order compact scheme. [ABSTRACT FROM AUTHOR]

Highlights • A vp-MPM is proposed for weakly compressible problems. • A slope limiter is employed to suppress spurious pressure oscillations. • The vp formulation is incorporated into the ICFEMP to suppress pressure oscillation. • The vp-MPM has much less extra variables than a Hu-Washizu principle based method. Abstract The weakly compressible material point method (WCMPM) suffers from volumetric-locking and numerical oscillation in modeling fluid flow and fluid-structure interaction problems. In this paper, a v-p formulation of the material point method (vp -MPM) is proposed for weakly compressible problems based on a two-field variational principle. As only the velocity v and the pressure p are the independent variables, the v - p formulation has much less extra variables than those based on the Hu-Washizu multi-field variational principle which takes the velocity, strain and stress as independent variables. The pressure is assumed independently in the control volume of each gird node. Spurious pressure oscillation reduces but still occurs at the interface of discontinuity due to large pressure gradient difference across the interface. Therefore, a slope limiter is employed to suppress the oscillation and the general interpolation functions are used to eliminate the cell-crossing error. In order to extend the method to the fluid-structure interaction problems, the v-p formulation is incorporated into the improved coupled finite element material point method. Several numerical examples are presented to validate the vp -MPM. [ABSTRACT FROM AUTHOR]

Highlights • The discrete adjoint mixing-plane is formulated and implemented on a legacy CFD code. • Automatic differentiation is used along hand-differentiation of high-level routines. • Adjoint-based sensitivities show good agreement with finite-differences. • Coupling between rows is evidenced by the computed sensitivities. • Multi-row aero-thermal problems can be efficiently handled. Abstract The use of high-fidelity computational fluid dynamics (CFD) tools in turbomachinery design has seen a continuous increase as a result of computational power growth and numerical methods improvement. These tools are often used in optimization environments, where gradient-based optimization algorithms are the most common due to their efficiency. In cases where the optimization contains a large number of design variables, the adjoint approach for calculating the gradients is beneficial, as it provides a way of obtaining function sensitivities with a computational cost that is nearly independent of the number of design variables. The interaction between adjacent blade rows is of utmost importance for the performance of multistage turbomachines. The most commonly used method to address these effects (i.e. coupling in the simulation of multiple rows) is the mixing-plane treatment, that has become a standard industrial tool in the design environment. In this paper, the formulation and implementation of an adjoint solver for multistage turbomachinery applications are presented, namely the adjoint counterpart of the mixing-plane formulation used in the direct solver. The solver is developed using the discrete ADjoint approach, where the partial derivatives required for the assembly of the adjoint system of equations are obtained using automatic differentiation tools. The sensitivity of several performance metrics relative to neighbor blade/hub row geometry and boundary conditions are shown to highlight the physical coupling in multi-row turbomachines. The verification of the adjoint multistage solver against the finite-difference approach is performed successfully with relative differences below 1 %. [ABSTRACT FROM AUTHOR]

Highlights • For fixed Rayleigh and Bingham numbers, the unyielded region is decreased by the augmentation of the porosity. • Heat transfer augments gradually as the porosity increases. • The growth of the Bingham number expands the unyielded sections in the cavity. Abstract Following recent studies by Huilgol and Kefayati [1,2], that developed a thermal Lattice Boltzmann method for different non-Newtonian fluids, we propose, in this paper, a general lattice Boltzmann method for thermal incompressible non-Newtonian fluids through porous media. Since no restrictions are placed on the constitutive equations in this method, the theoretical development can be applied to all fluids, whether they be Newtonian, or power law fluids, or viscoelastic and Bingham fluids. To validate the accuracy of the method, natural convection in a porous cavity was studied and compared with previous studies. Next, we employ the model to simulate natural convection of power-law and Bingham fluids in a porous cavity. [ABSTRACT FROM AUTHOR]

Highlights • A new grid system is developed to detect the areas needing high-resolution mesh. • The grid system can locally refine the grid for surface water flow simulation. • The method could accelerate the model by about 3 times without accuracy loss. • The grid system is very suitable for integrating into the shallow water flow model. • The new grid system based model could be used for efficient and accurate prediction. Abstract Aiming at improving the computational efficiency without accuracy losses for surface water flow simulation, this paper presents a structured but non-uniform grid system incorporated into a Godunov-type finite volume scheme. The proposed grid system can detect the key topographic features in the computational domain where high-resolution mesh is in need for reliably solving the shallow water equations. The mesh refinement is automatically carried out in these areas while the mesh in the rest of the domain remains coarse. The criterion determining the refinement is suggested by a dimensionless number with a fixed value of 0.2 after sensitivity analysis. Three laboratory and field-scale test cases are employed to demonstrate the performance of the model for flow simulations on the new non-uniform grids. In all of the tests, the grid system is shown to successfully generate high-resolution mesh only in those areas with abruptly changing topographic features that dominate the flooding processes. To produce numerical solutions of similar accuracy, the non-uniform grid based model is able to accelerate by about two times comparing with the fine uniform grid based counterpart. [ABSTRACT FROM AUTHOR]

Highlights • A direct-forcing IB projection method is proposed for solving FSI problems. • It is a two-stage approach with a prediction-correction process. • A virtual force is introduced and distributed on the immersed solid bodies. • This method allows larger time step than traditional direct-forcing IB methods. • Accuracy of the velocity field is super-linear in space in 1, 2 and maximum norms. Abstract In this paper, we propose a simple and novel direct-forcing immersed boundary (IB) projection method in conjunction with a prediction-correction (PC) process for simulating the dynamics of fluid-solid interaction problems, in which each immersed solid object can be stationary or moving in the fluid with a prescribed velocity. The method is mainly based on the introduction of a virtual force which is distributed only on the immersed solid bodies and appended to the fluid momentum equations to accommodate the internal boundary conditions at the immersed solid boundaries. More specifically, we first predict the virtual force on the immersed solid domain by using the difference between the prescribed solid velocity and the computed velocity, which is obtained by applying the Choi–Moin projection scheme to the incompressible Navier–Stokes equations on the entire domain including the portion occupied by the solid bodies. The predicted virtual force is then added to the fluid momentum equations as an additional forcing term and we employ the same projection scheme again to correct the velocity field, pressure and virtual force. Although this method is a two-stage approach, the computational cost of the correction stage is rather cheap, since the associated discrete linear systems need to be solved in the correction stage are same with that in the prediction stage, except the right-hand side data terms. Such a PC procedure can be iterated to form a more general method, if necessary. The current two-stage direct-forcing IB projection method has the advantage over traditional one-stage direct-forcing IB projection methods, consisting of the prediction step only, by allowing much larger time step, since traditional methods generally request quite small time step for flow field relaxed and adjusted to the solid body movement even using implicit scheme. Numerical experiments of several benchmark problems are performed to illustrate the simplicity and efficient performance of the newly proposed method. Convergence tests show that the accuracy of the velocity field is super-linear in space in all the 1-norm, 2-norm, and maximum norm. We also find that our numerical results are in very good agreement with the previous works in the literature and one correction at each time step appears to be good enough for the proposed PC procedure. [ABSTRACT FROM AUTHOR]

Highlights • Generalization of the 2014 version of the ZIBC combining RANS/LES and the IB method. • Extended presentation of the Zonal Immersed Boundary Conditions approach. • First RANS/LES and IBC application to a full space launcher at high Reynolds number. • ZDES/IBC is highly validated for both the statistical field and the spectral content. Abstract One of the next foreseen challenges in CFD consists in the capability to simulate quantitatively the spectral content of the turbulent flow around realistic geometries. In this context, the present work focuses on a new methodology named ZIBC standing for Zonal Immersed Boundary Conditions enabling to account for complex configurations at high Reynolds numbers. The numerical strategy allowing the coupling between a turbulence modeling method (e.g. RANS, URANS, ZDES, LES or DNS) and IBC (Immersed Boundary Conditions) is detailed. In this paper, the modeling method retained is the Zonal Detached Eddy Simulation (ZDES) which has reached a high level of maturity on turbulent separated flow simulations. This methodology is applied to a full space launcher configuration to assess its capability to return the interactions between the technological details, modeled with IBC, and the simplified afterbody, modeled with a body-fitted (BF) approach consisting in classical no-slip boundary conditions, in the turbulent flow field surrounding the main stage of the space launcher afterbody. The proposed method is thoroughly assessed on a realistic geometry of the European Ariane 5 launcher and the ZIBC simulation is successfully compared with the available experiments. [ABSTRACT FROM AUTHOR]

Highlights • Investigations of RANS and hybrid RANS-LES models for the Ahmed body. • Accurate prediction of the flow for the slant angle 35° by all turbulence models. • Failure of RANS models to predict the flow for the slant angle 25°. • Better prediction of the flow for the slant angle 25° with the hybrid RANS-LES models. • IDDES model: only model to predict the bubble recirculation on the slant. Abstract This paper presents an investigation of RANS and DES models for the Ahmed body with 25° and 35° slant angles. The Reynolds number, based on the height of the model and the upstream velocity, is 7.68× 105. Two RANS (Reynolds Averaged Navier–Stokes) models are used: the k − ω SST of Menter and the EARSM (Explicit Algebraic Stress Model), based on the k − ω model. Two hybrid RANS-LES (Large Eddy Simulation) models are used: a DES (Detached Eddy Simulation) and an IDDES (Improved Delay Detached Eddy Simulation). These hybrid models are also based on the k − ω model. The flow for the slant angle 35° is well predicted by all turbulence models with a slight advantage for the IDDES model. For the flow with the slant angle 25°, only the IDDES hybrid RANS-LES model predicts the recirculation bubble on the slant. It is concluded that the IDDES model is the only turbulence model that gives good agreements with the experimental data. [ABSTRACT FROM AUTHOR]

Highlights • A scale-truncation condition for large-eddy simulation is derived from first principles. • This condition is applied to an eddy-viscosity model. • The resulting eddy-viscosity model is successfully tested for turbulent channel flow. Abstract This paper is about models for large-eddy simulation of turbulent flow that truncate the small scales of motion for which numerical resolution is not available by making sure that they do not get energy from the larger, resolved, eddies. The resolved scales are defined with the help of a box filter. The eddy dissipation is determined in such a way that the production of too small, box-fitting, scales is counteracted. This dissipation-production balance is worked out with the help of Poincaré's inequality, which results in a condition that depends on the invariants of the velocity gradient. If the filter box is anisotropic the truncation condition is to be scaled in order to account for the anisotropy in the right way. The scaled truncation condition is applied to an eddy-viscosity model. This model is discretized and equipped with a Schumann filter. It is successfully tested for homogeneous turbulence as well as for turbulent channel flow. [ABSTRACT FROM AUTHOR]

Highlights • A set of practical inlet boundary conditions with available measured data is investigated. • Well-posedness for specifying the total temperature, the total pressure and the tangential velocity is proved. • An eigenmode-analysis is used to predict convergence rates to steady state. • Numerical simulations verify the theoretical predictions. Abstract To impose boundary conditions, data at the boundaries must be known, and consequently measurements of the imposed quantities must be available. In this paper, we consider the two most commonly used inflow boundary conditions with available data for internal flow calculations: the specification of the total temperature and total pressure. We use the energy method to prove that the specification of the total temperature and the total pressure together with the tangential velocity at an inflow boundary lead to well-posedness for the linearized compressible Euler equations. Next, these equations are discretized in space using high-order finite-difference operators on summation-by-parts form, and the boundary conditions are weakly imposed. The resulting numerical scheme is proven to be stable and the implementation of the corresponding nonlinear scheme is verified with the method of manufactured solutions. We also derive the spectrum for the continuous and discrete problems and show how to predict the convergence rate to steady state. Finally, nonlinear steady-state computations are performed, and they confirm the predicted convergence rates. [ABSTRACT FROM AUTHOR]

Wing flexibility affects the flight performance of flapping-wing micro air vehicles. In this paper, we present a computational approach for the aeroelastic analysis of realistic insect-like flexible flapping wings with hovering and forward-flight modes. A three-dimensional preconditioned Navier–Stokes solver is used with a deforming mesh technique for the aerodynamic analysis of a flapping wing. For the structural analysis, co-rotational (CR) finite elements and CR shell elements are used. As seen from the numerical analysis, wing flexibility leads to thrust increments with the increasing flapping frequency. The advance ratio, however, is the cause of the thrust decrease for flexible flapping wings with high flapping-frequency motions. [ABSTRACT FROM AUTHOR]

The importance of the two-phase flow model relies upon the correct simulation of specific problems in which the passive tracer model fails; however, the mathematical and numerical models need to be improved in order to reproduce fluid-solid particle interactions of greater complexity. Such is the case with regard to simulating erosion patterns suffered upon horizontal granular beds by means of a vertical water jet as shown here. Moreover, sequential platforms have proven to be insufficient in providing the required computational power needed to obtain fast and detailed simulations. In this paper, a fully parallel algorithm for a two-dimensional x / z two-phase Eulerian approach is presented and applied for the numerical solution of the erosion of sediment beds. The parallelization is designed by a row and column block domain decomposition technique using a distributed memory platform with Message Passing Interface (MPI). Arising from the numerical method, a Poisson problem for the pressure is solved at each time step. The discretization results in a non-symmetric variable-coefficient linear system which is solved using several parallel Successive Over-Relaxation (SOR) algorithms, including partitioning and coloring methods. The specification of the optimal relaxation parameter to achieve efficiency is found numerically. Results show that SOR methods achieve faster convergence rates and the simulation time achieves an order similar to that required for the typical, widely-used Bi-Conjugate Gradient Stabilized (Bi-CGSTAB) method. The performances of the algorithms are evaluated in terms of speedup and efficiency. The results indicate that the parallel code significantly improves the results of the sequential calculation in general. [ABSTRACT FROM AUTHOR]

In this paper, based on the perturbed fluxes of all candidate fluxes used in the traditional fifth-order WENO scheme, a fifth-order accurate perturbational weighted essentially non-oscillatory (P-WENO) scheme is developed. First, a corollary about the accuracy of a kind of conservative schemes is generalized and proved. Then, based on the corollary and the idea of numerical perturbation, the perturbed fluxes, which are one order higher than the traditional candidate ones of the fifth-order WENO scheme, are obtained. Furthermore, we derive the necessary and sufficient conditions for the fifth-order convergence of the new weighted scheme constructed by using the new perturbed fluxes and find that they are one order lower than those derived by Henrick et al. for the traditional fifth-order WENO scheme. Thus, the new weighted scheme, which uses the same weights of the WENO-Z scheme and the perturbed fluxes, can meet the necessary and sufficient condition for fifth-order convergence even at critical points. The resulted P-WENO scheme actually provides a novel method to decrease the numerical dissipation of traditional WENO schemes. Numerical examples are presented to verify the accuracy, robustness and low-dissipation of the new scheme. [ABSTRACT FROM AUTHOR]

This paper reports on a numerical model expressly developed to inquire about the role of solidification in determining the properties of the emerging surface-tension-driven flow in typical models of oxide crystal growth. Following earlier efforts in the literature, we consider substances which have already enjoyed a widespread consideration for such a kind of studies, i.e. sodium nitrate (NaNO 3 , Pr = 8) and succinonitrile (SCN, Pr = 23). Specific numerical examples are expressly elaborated and presented to provide inputs for an increased understanding of the main cause-and-effect relationships driving fluid flow and determining its properties. It is shown that, by interfering with the hydrothermal mechanism, namely the preferred mode of instability of Marangoni flow over a wide range of substances and conditions, solidification contributes to the chaoticity of the system by increasing the complexity of the emerging patterns and enriching the spectral content of the flow. [ABSTRACT FROM AUTHOR]

This paper extends a recently proposed multi-region based numerical wave tank (Martínez-Ferrer et al. [1]) to solve water entry problems in naval engineering. The original static linking strategy is developed to enable the dynamic coupling of several moving regions. This permits the method to deal with large-amplitude motions for structures slamming into water waves. A background grid and one or more component meshes are firstly generated to overlay the whole computational domain and the sub-domains surrounding the structures, respectively. During computation, the background mesh is fixed while the small grids move freely or as prescribed without deformation and regeneration. This effectively circumvents the large and often excessive error-prone dynamic deformation of a single-block mesh as well as the complex and time-consuming mesh regeneration. Test cases of dam breaking with and without obstacles are first conducted to verify the developed code by comparing the numerical solution against experimental data. Then the new code is used to solve prescribed and free-fall water entry problems. The obtained results agree well with experimental measurements and other computational results reported in the literature. [ABSTRACT FROM AUTHOR]

Process design, especially in the chemical industry, often requires a detailed understanding and accurate quantification of interfacial mass transfer. Experimental investigations, however, are often infeasible as required measurement quantities and locations are inaccessible. Thus, Direct Numerical Simulations (DNS) have become a viable tool for the detailed study of mass transfer processes. This paper presents a numerical modelling framework for the simulation of dilute species transfer based on an algebraic Volume-of-Fluid method, aiming at the deduction of an improved closure model for interfacial species transfer from single rising bubbles. To this end, the Continuous Species Transfer (CST) model [18] and state-of-the-art high performance computing techniques are employed. [ABSTRACT FROM AUTHOR]

For a Lagrangian scheme solving the compressible Euler equations in cylindrical coordinates, two important issues are whether the scheme can maintain spherical symmetry (symmetry-preserving) and whether the scheme can maintain positivity of density and internal energy (positivity-preserving). While there were previous results in the literature either for symmetry-preserving in the cylindrical coordinates or for positivity-preserving in cartesian coordinates, the design of a Lagrangian scheme in cylindrical coordinates, which is high order in one-dimension and second order in two-dimensions, and can maintain both spherical symmetry-preservation and positivity-preservation simultaneously, is challenging. In this paper we design such a Lagrangian scheme and provide numerical results to demonstrate its good behavior. [ABSTRACT FROM AUTHOR]

In this paper we analyze the use of time splitting techniques for solving shallow water equations. We discuss some properties that these schemes should satisfy so that interactions between the source term and the shock waves are controlled. This work shows that these schemes must be well balanced in the meaning expressed by Greenberg and Leroux [7]. More specifically, we analyze in what cases it is enough to verify an Approximate C-property and in which cases it is required to verify an Exact C-property (see [1, 2]). We also discuss this technique in two dimensions and include some numerical tests in order to justify our argument. [ABSTRACT FROM AUTHOR]

In this paper we extend our previous two-dimensional tandem wing study to three-dimensions. In our previous study we found that vortex interactions highly depend on the phase lag angle and spacing between the forewing and hindwing. In this paper the effect of phase lag angle between the fore and hind wings on the wing–wing interactions, force production, and efficiency of the hindwing was studied for three different phase lag angles, 0°, 90° and 180°. The spacing used between the forewing and hindwing was one chord. A single frequency sinusoidal pitch–plunge motion was used at a Strouhal number of 0.3 and a Reynolds number of 200. The aspect ratio of the three dimensional wing was two. The simulations were based on the incompressible Navier–Stokes equations, discretized on overlapping grids. The wing motions were prescribed by a series of composed transformation matrices. A moving overlapping grid technique will be used to handle the moving boundary problems. It was found that the three dimensional cases exhibited a spanwise variation in the LEV structure and a weaker LEV formation at midspan compared to the two-dimensional cases with the same kinematics. The spanwise variation resulted in weaker vortex interactions between the fore and hind wing than predicted by the two dimensional study. [ABSTRACT FROM AUTHOR]

The paper is devoted to different approaches of a pressure–velocity coupling method to account for density variations in cavitating two-phase flow simulations. Results obtained from two strategies are investigated in detail. A simpler engineering approach associated the variations of the local density solely with the changes of the vapor-volume fraction computed by a cavitation model and assumes incompressible vapor and water phases. A more elaborate method additionally accounts for the compressibility of the two individual fluid phases. Numerical issues of significance for engineering applications are discussed in the paper, such as the occurrence of ill-conditioned matrices or cavitation-model dependencies. The single-phase verification and validation study refers to prominent aerodynamic benchmarks, i.e. a convergent-divergent nozzle flow and the flow over a bump in a channel. Cavitating flow validations are concerned with a stationary flow over a hydrofoil. An unsteady cavitating flow over a NACA0015 hydrofoil is computed to demonstrate merits of the implemented compressible fluid method to simulate sheet and vapor cavitation including the collapse of a vapor cloud followed by a shock wave formation and propagation. Results demonstrate that the predicted cavitation pattern of the two approaches are very similar and the compressible flow model is only required when attention is directed to the evolution of pressure waves of the collapsing cavities, e.g. in erosion studies. [ABSTRACT FROM AUTHOR]

This paper investigates effects of ducting on power output from vertical axis hydro-current turbines. A numerical two-dimensional method based on the potential flow theory is developed for calculation of non-dimensional power output from these turbines. In this method, the blades are represented by vortex filaments. The vortex shedding from the blades is modeled by discrete vortices. A boundary element method is used to incorporate the duct shape which is represented by a series of panels with constant distributions of sources and doublets. The aerodynamic loading on the blades are calculated using a quasi-steady modeling. A time-marching scheme is used for implementation of the numerical method. The results of this method are compared with experimental results for a turbine model. A good correlation between the numerical and experimental results is obtained for tip speed ratios equal and higher than 2.25. However due to a lack of dynamic stall modeling, the numerical method is not able to predict power output accurately at lower tip speed ratios wherein effects of dynamic stall are significant. Both numerical and experimental results also showed that the power output from a turbine can increase significantly when it is enclosed within a well-designed duct. The maximum power output of the turbine model investigated in this paper showed a 74% increase when the turbine is operating within the duct relative to the case it is in free-stream conditions. [ABSTRACT FROM AUTHOR]

In this paper, we construct a new numerical method to solve the reactive Euler equations to cure the numerical stiffness problem. The species mass equations are first decoupled from the reactive Euler equations, and then they are further fractionated into the convection step and the reaction step. In the convection step, by introducing two kinds of Lagrangian points (cell-point and particle-point), a dual information preserving (DIP) method is proposed to resolve the convection characteristics. In this new method, the information (including the transport value and the relative coordinates to the center of the current cell) of the cell-point and that of the particle-point are updated according to the velocity field. The information of the cell-point in a cell can effectively restrict the incorrect reaction activation caused by the numerical dissipation, while the information of the particle-point can help to preserve the sharp shock front once the strong shock waves are formed. Hence, by using the DIP method, the spurious numerical propagation phenomenon in stiff reacting flows is effectively eliminated. In addition, a numerical perturbation method is also developed to solve the fractional reaction step (ODE equation) to improve the stability and efficiency. A series of numerical examples are presented to validate the accuracy and robustness of the new method. [ABSTRACT FROM AUTHOR]

In this paper, we propose an accurate Riemann-solver free method for a coupled system modeling shallow water flows, sediment transport and rapid bed erosion. The hydrodynamic model solving shallow water equations (SWEs) is coupled with the sediment transport equation and the morphodynamic model. A Godunov-type central-upwind scheme is proposed to numerically solve the resulting system based on the technique that using two different pairs of local wave speeds to estimate numerical fluxes for hydrodynamic and morphodynamic models, respectively. The proposed technique leads to accurate results for the computation of the morphodynamic model. The proposed scheme is based on computationally efficient techniques and do not require analytical expressions of the eingenstructure of the system. A well-balanced discretization of the bed-slope terms is developed in framework of the coupling approach. Finally, we demonstrate the robustness and accuracy of the proposed numerical scheme for the coupled system using several numerical tests. [ABSTRACT FROM AUTHOR]

Central discontinuous Galerkin (CDG) methods are a family of high order numerical methods, which evolve two sets of numerical solutions defined on overlapping meshes and do not employ the numerical fluxes at element interfaces as in discontinuous Galerkin methods. However, evolving two sets of numerical solutions makes the CDG method relatively time-consuming. In this paper, we present a reconstructed central discontinuous Galerkin (RCDG) method for conservation laws. In this scheme, we reconstruct an approximate solution by projecting the numerical solution defined on the primal mesh into the approximate space defined on the dual mesh in the L 2 sense. As a consequence, the reconstructed approximate solution plays a role as an alternative for the numerical solution defined on the dual mesh in the CDG method. Numerical examples demonstrate that the RCDG method is not only simpler and easier to implement than the CDG method but also reduces the computational cost considerably without sacrificing the high order accuracy of the CDG method. [ABSTRACT FROM AUTHOR]

In this paper, a new interface treatment technique for multi-phase meshless methods is proposed for two-dimensional simulations. It enables the interface conditions to be applied effectively on the interface points involving interface tension and high viscosity. This technique is incorporated in the Meshless Local Petrov–Galerkin method with the Rankine source solution (MLPG_R) and the model predictions are validated through a number of standard test cases. Convergent results that agreed well with both available analytical and numerical solutions from other methods are obtained in simulations of square-droplet deformation, capillary wave, bubble rising and Rayleigh–Taylor instability. In these cases, sharp pressure discontinuity at the interface is well predicted with depressed parasitic current and the capability of the technique in dealing with high viscosity is comprehensively demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, we describe a higher-order finite volume solver for the RANS solution of turbulent compressible flows on unstructured meshes. Considering that higher-order least-squares reconstruction suffers from poor accuracy on highly anisotropic meshes with curvature, we propose a modification to this method which highly improves the accuracy of solution approximation and output quantities. In addition, robust implementation and coupling of a RANS turbulence model with a higher-order finite volume solver is described and an efficient solution strategy is adopted for the convergence to the steady-state solution. We present our results, ranging from second- to fourth-order, for the test case of turbulent flat plate, subsonic and transonic flows over two-dimensional airfoils and also turbulent flow over a multi-element configuration. These results are verified by comparison against well-established numerical and experimental values in the literature. Our results show the advantages of higher-order methods in obtaining a more accurate solution with fewer degrees of freedom and also fast and efficient convergence to the steady-state solutions. [ABSTRACT FROM AUTHOR]

In this paper we consider a multiscale phase-field model for capillarity-driven flows in porous media. The presented model constitutes a reduction of the conventional Navier–Stokes–Cahn–Hilliard phase-field model, valid in situations where interest is restricted to dynamical and equilibrium behavior in an aggregated sense, rather than a precise description of microscale flow phenomena. The model is based on averaging of the equation of motion, thereby yielding a significant reduction in the complexity of the underlying Navier–Stokes–Cahn–Hilliard equations, while retaining its macroscopic dynamical and equilibrium properties. Numerical results are presented for the representative 2-dimensional capillary-rise problem pertaining to two closely spaced vertical plates with both identical and disparate wetting properties. Comparison with analytical solutions for these test cases corroborates the accuracy of the presented multiscale model. In addition, we present results for a capillary-rise problem with a non-trivial geometry corresponding to a porous medium. [ABSTRACT FROM AUTHOR]

This paper aims at understanding the numerical dissipation mechanisms related to the Spectral Difference (SD) method in the context of three-dimensional (3D) turbulence. The numerical dissipation stemming from the discretization of the convective terms is studied by performing inviscid computations of the transitional Taylor–Green vortex and isotropic turbulence configurations. The Taylor–Green vortex computations show that the increase in the order of accuracy restricts the numerical dissipation to smaller scales which, in turn, leads to a better representation of transitional mechanisms. However, isotropic turbulence computations using a fifth-order accuracy or above show obvious manifestations of under-resolution (such as the onset of oscillations and numerical noise), which suggests that the high-order numerical dissipation alone is unable to mimic the dissipation originating from sub-grid scales in the case freely decaying turbulence. Computations of the channel flow configuration at R e τ = 1000 at typical large-eddy simulation resolutions show that under-resolved SD discretizations using a high order of accuracy (fifth and sixth) lead to an excellent prediction of the wall-friction, the velocity profiles, the turbulent structures near the wall and the energy spectra, while lower order discretizations lead to an underestimation of the wall-friction and globally a poor representation of wall-bounded turbulence. The present study emphasizes the benefit of using high-order SD discretizations for an accurate representation of turbulent phenomena (namely, transitional and wall-bounded turbulence) but also the necessity of combining this approach with dynamic large-eddy simulation models or appropriate regularization techniques which would activate only where needed to recover physically consistent results, e.g. , in regions where fully developed turbulence is present. [ABSTRACT FROM AUTHOR]

The Ripa model is a non-homogeneous hyperbolic system with a non-zero source term, which is deduced from the shallow water equations by incorporating the horizontal temperature gradients. The Ripa model can maintain steady state solutions in which the flux gradients are non-zero but exactly balanced by the source term. It is a challenging task to design genuinely high order accurate numerical schemes which preserve exactly these steady state solutions. In this paper we design high order well-balanced finite difference weighted essentially non-oscillatory (WENO) schemes to this model. Rigorous theoretical analysis as well as extensive 1D and 2D numerical results all demonstrates that the present schemes share high order accuracy, maintain the well-balanced property, and keep good resolution for both smooth and discontinuous solutions. [ABSTRACT FROM AUTHOR]

Abstract: Despite the widespread use of fully three-dimensional Computational Fluid Dynamics (CFD) techniques, axisymmetric flow models still represent a key tool in turbomachinery design. In this paper, a novel method for the numerical solution of axisymmetric flow models for turbomachinery is presented and demonstrated for two cases, both relevant for the industrial perspective. The key feature of the proposed method is that the flow tangency condition to the blade mean line is enforced with a penalty term, which can also be interpreted as an immersed boundary technique. Differently from the techniques commonly applied for the solution of this kind of flows, the proposed method does not require additional constraint equations to be solved in bladed regions and is therefore very simple to be implemented into existing axisymmetric CFD codes. The techniques employed to deal with flows of high incidence angle (misalignments between the actual flow and the direction imposed by the blade) and to account for the aerodynamic losses and the blade blockage are also thoroughly discussed. The method has been implemented as an extension of the zFlow code for the numerical solution of the Euler equations in cylindrical coordinates, which is based on an hybrid finite element/finite volume space approximation, an implicit time integration scheme, and can deal with fluids of arbitrarily complex equations of state. The details of the numerical method are fully described in the paper. The performance of the developed code is demonstrated by the results obtained in the simulation of a single-stage axial fan, compared against a fully three-dimensional CFD simulation. The potentialities for more complex transonic flow conditions are finally demonstrated by the calculation of a double-stage low pressure steam turbine. [Copyright &y& Elsevier]

Abstract: During floods, the density of river water usually increases due to the increase in the concentration of the suspended sediment that the river carries, causing the river to plunge underneath the free surface of a receiving water basin and form a turbidity current that continues to flow along the bottom. The study and understanding of such complex and rare phenomena is of great importance, as they constitute one of the major mechanisms for suspended sediment transport from rivers into the ocean, lakes or reservoirs. In the present paper a previously tested and verified numerical model is applied in laboratory scale numerical experiments of continuous, high density turbidity currents. The turbidity currents are produced by the steady discharge of fresh water – suspended sediment mixtures, into an inclined channel which is connected at its downstream end to a wide horizontal tank. Both, channel and tank are initially filled with fresh water. This configuration serves as a simplified experimental analog of natural, hyperpycnal turbidity currents that are formed at river outflows in the sea, lakes or reservoirs and usually travel within subaqueous canyon-fan complexes. The main aim is to investigate the exact qualitative and quantitative effect of fundamental, flow controlling parameters in the hydrodynamic and depositional characteristics of continuous, high density turbidity currents. According to the authors’ best knowledge, the present paper constitutes the first attempt in the literature, where the isolated effects of each individual controlling parameter as well as their relative importance on the hydrodynamic characteristics of continuous, high-density turbidity currents are quantitatively evaluated in detail. The numerical model used, is based on a multiphase modification of the Reynolds Averaged Navier–Stokes equations (RANS). For turbulence closure the Renormalization-group (RNG) k–ε model is applied, which is an enhanced version of the widely used standard k–ε model. [Copyright &y& Elsevier]

Abstract: A boundary condition-enforced immersed boundary method is presented in this paper for simulation of free and forced convection problems with Dirichlet-type boundary condition. The heat source/sink is introduced into the energy equation to model the effect of immersed boundary. Different from previous works, in this paper, the heat source/sink is not pre-calculated, but determined implicitly in such a way that temperature at the immersed boundary interpolated from the corrected temperature field accurately satisfies the thermal condition. The main advantage of the proposed method lies in its simple concept, easy implementation and robustness in stability. Another important contribution of the paper is that it presents two efficient ways to calculate the average Nusselt number. They are based on temperature correction at Eulerian points and heat flux at Lagrangian points, in which no approximation for temperature gradients is needed. Numerical experiments for both forced convection and natural convection problems have been conducted to validate the capability and efficiency of the present method and proposed two ways to calculate the average Nusselt number. Good agreements with available data in the literature have been achieved. [Copyright &y& Elsevier]

Abstract: This paper illustrates the mechanism of the U-shaped vortex formation, which has been found by both experiments and DNS in boundary-layer transition. The main goal of this paper is to find how the U-shaped vortex is formed and further developed. According to the results obtained by our direct numerical simulation (DNS) with high order accuracy, the U-shaped vortex is part of the large coherent vortex structure. This new finding is quite different from existing theories which describe that the U-shaped vortex is a secondary vortex induced by second sweeps, and it is newly formed as the head of young turbulence spot and finally breaks down to small pieces. However, it is found that the U-shaped vortex is neither generated by the second sweeps nor the consequent positive spikes. Actually, the U-shaped vortex is induced by the secondary vortices and the solid wall. The new finding also shows the U-shaped vortex is a vortex tube but not the heading wave. In addition, it is found that the U-shaped vortex has the same vorticity sign as the original Λ-shaped vortex legs, which means the U-shaped vortex is not secondary but tertiary. It serves as an additional channel to provide vorticity to support the multiple ring-like vortices when the original vortex tube is stretched and multiple rings are generated. [Copyright &y& Elsevier]

Abstract: Computational Fluid Dynamics (CFD) analysis has become a useful research and design instrument albeit with errors and uncertainties. Appropriate standards and protocols for increasing confidence and reliability need to be identified and applied. These requirements become more relevant as improvements in hardware, software and user competence increase. Advances in these sectors have led to the increased use of CFD codes in the applied research industry. In the discussion on the opportunities of applying Quality Assurance to Research and Development (R&D) activities, and on investigating methodologies (numerical or experimental), CFD results need to be qualified; rules, and procedures should be instated and followed. This paper proposes a methodological approach to qualify CFD, named Q3 approach. The approach is based on three interdependent, but related, dimensions: software reliability, user knowledge and process control. Applying the quality of CFD analysis to industrial problems, while following the principles of Quality Assurance, is of particular concerned. The paper aims to focus on the dimensions of user knowledge and process control, which are often overlooked and are of great importance when determining the quality of CFD. The approach discussed here refers to a typical R&D department in a Small or Medium Enterprise (SME) where a CFD code is used as a support tool for process or product development, optimisation and/or innovation. Within the three dimensions, software reliability immediately refers to Verification and Validation (V&V) procedures, a well known issue for those who are involved in code and model development. User knowledge and process control play a vital role in achieving accurate results and cannot be neglected, as per the principles of Quality Assurance. Therefore it is vital to provide continuous CFD analyst training to industrial professionals. Applying a CFD cycled process, which refers to the cyclic logic proposed in Quality Assurance, may face some constrains in specific industrial scenarios. A protocol will serve as an instrument of process control. Within the protocol, the phases of Calculation, Verification and Validation as well as User Defined Model Verification represent critical elements, and are specifically detailed and structured in accordance with the RADAR logic (Results, Approach, Deploy, Assess, Refine) used for Quality Assurance Management. In the case a specific study does not rely on experimental data, an alternative is proposed. The protocol is designed as a single tool that responds to both the need for qualified CFD and the requirement of internal or external audit of Quality Assurance (as far as calculations are concerned), thus increasing cost and personnel efficiency. [Copyright &y& Elsevier]

Abstract: This paper applies a transient multiscale approach to model ventilation flows and fires in a tunnel domain. The multiscale model couples dynamically a Computational Fluid Dynamics (CFD) solver with a simple 1D network model, allowing for a more rational use of the computational resources without loss of accuracy. The 1D network models tunnel regions where the flow is fully developed (far field), while detailed CFD models regions where flow conditions require 3D resolution (near field). The paper describes both numerical models and gives emphasis to the discussion of the coupling algorithm and the control of the numerical error. Compared to full CFD, the multiscale model provides a reduction of the required computing time by 40 times without significant loss of accuracy. The methodology has been applied to study the transient flow interaction between a growing fire and a ramping-up ventilation system in a modern tunnel of 7m diameter section and 1.2km in length. Different ventilation scenarios are investigated to provide the timing to reach the critical velocity at the seat of the fire, and to remove the upstream back layering. The results allow for simultaneous optimization of the ventilation and detection systems. The multiscale methodology represents the most feasible tool to conduct accurate simulations in long tunnel domains, when the limitation of the computational cost becomes too restrictive. [Copyright &y& Elsevier]

Abstract: In this paper, we introduce a general principle for constructing robust and accurate viscous discretization, which is applicable to various discretization methods, including finite-volume, residual-distribution, discontinuous-Galerkin, and spectral-volume methods. The principle is based on a hyperbolic model for the viscous term. It is to discretize the hyperbolic system by an advection scheme, and then derive a viscous discretization from the result. A distinguished feature of the proposed principle is that it automatically introduces a damping term into the resulting viscous scheme, which is essential for effective high-frequency error damping and, in some cases, for consistency also. In this paper, we demonstrate the general principle for the diffusion equation on uniform grids in one dimension and unstructured grids in two dimensions, for node/cell-centered finite-volume, residual-distribution, discontinuous-Galerkin, and spectral-volume methods. Numerical results are presented to verify the accuracy of the derived diffusion schemes and to illustrate the importance of the damping term for highly-skewed typical viscous grids. [Copyright &y& Elsevier]

Abstract: A number of Game Strategies (GS) have been developed in past decades. They have been used in the fields of economics, engineering, computer science and biology due to their efficiency in solving design optimization problems. In addition, research in multi-objective (MO) and multidisciplinary design optimization (MDO) has focused on developing robust and efficient optimization methods to produce a set of high quality solutions with low computational cost. In this paper, two optimization techniques are considered; the first optimization method uses multi-fidelity hierarchical Pareto optimality. The second optimization method uses the combination of two Game Strategies; Nash-equilibrium and Pareto optimality. The paper shows how Game Strategies can be hybridised and coupled to Multi-Objective Evolutionary Algorithms (MOEA) to accelerate convergence speed and to produce a set of high quality solutions. Numerical results obtained from both optimization methods are compared in terms of computational expense and model quality. The benefits of using Hybrid-Game Strategies are clearly demonstrated. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to present different fractional step schemes in the algebraic context to solve the incompressible Navier–Stokes equations, test them and pick the best one in terms of efficiency and robustness. The equivalence between fractional step schemes and iterative methods for the pressure Schur complement system has been well established in the literature. For example, the classical incremental projection scheme can be associated with a Richardson iteration for the pressure Schur complement plus a correction to enforce the mass conservation. We introduce in this paper an Orthomin(1) iteration which minimizes the Schur complement residual at each solver iteration by using, in the updating step, a factor dynamically computed. Two versions are considered, namely the momentum preserving and continuity preserving versions. The method is compared to the classical Richardson method, including the continuity and momentum preserving versions. In addition, two Schur complement preconditioners are considered and compared, based on the approximation of the weak Uzawa operator. From the implementation point of view, the benefit of the method is two fold. On the one hand, it can be easily implemented starting from the global matrix of the monolithic scheme, without changing the assembly. On the other hand, it enables the use of simple algebraic solvers without the need for complex preconditioners; this is a requirement for massively parallel computers. The four methods are finally tested and compared through the solution of numerical examples. The main conclusion is that with very few additional computation, the Orthomin(1) iteration largely improves the global convergence properties of the fractional schemes here presented. [Copyright &y& Elsevier]

Abstract: For aeroacoustics problems, the nonlinear Euler equations are often written in primitive variables in which the pressure is treated as a solution variable. In this paper, absorbing boundary conditions based on the Perfectly Matched Layer (PML) technique are presented for nonlinear Euler equations in primitive variables. A pseudo mean flow is introduced in the derivation of the PML equations for increased efficiency. Absorbing equations are presented in unsplit physical primitive variables in both the Cartesian and cylindrical coordinates. Numerical examples show the effectiveness of the proposed equations although they are not theoretically perfectly matched to the nonlinear Euler equations. The derived equations are tested in numerical examples and compared with the PML absorbing boundary condition in conservation form that was formulated in an earlier work. The performance of the PML in primitive variables is found to be close to that of the conservation formulation. A comparison with the linear PML in nonlinear problems is also considered. It is found that using nonlinear absorbing equations presented in this paper significantly improves the performance of the absorbing boundary condition for strong nonlinear cases. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we attack the problem of devising a finite volume method for computational fluid dynamics and related phenomena which can deal with complex geometries while attaining high-orders of accuracy and spectral convergence at a reasonable computational cost. As a first step towards this end, we propose a control volume finite element method for the solution of the advection–diffusion equation. The numerical method and its implementation are carefully tested in the paper where h- and p-convergence are checked by comparing numerical results against analytical solutions in several relevant test-cases. The numerical efficiency of a selected set of operations implemented is estimated by operation counts, ill-conditioning of coefficient matrices is avoided by using an appropriate distribution of interpolation points and control-volume edges. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present an efficient numerical method for two-phase immiscible flow in porous media with different capillarity pressures. In highly heterogeneous permeable media, the saturation is discontinuous due to different capillary pressure functions. One popular scheme is to split the system into a pressure and a saturation equation, and to apply IMplicit Pressure Explicit Saturation (IMPES) approach for time stepping. One disadvantage of IMPES is instability resulting from the explicit treatment for capillary pressure. To improve stability, the capillary pressure is usually incorporated in the saturation equation which gradients of saturation appear. This approach, however, does not apply to the case of different capillary pressure functions for multiple rock-types, because of the discontinuity of saturation across rock interfaces. In this paper, we present a new treatment of capillary pressure, which appears implicitly in the pressure equation. Using an approximation of capillary function, we substitute the implicit saturation equation into the pressure equation. The coupled pressure equation will be solved implicitly and followed by the explicit saturation equation. Five numerical examples are provided to demonstrate the advantages of our approach. Comparison shows that our proposed method is more efficient and stable than the classical IMPES approach. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new system of compact discrete filters based on a seven-point stencil and pentadiagonal matrix formulation which can be readjusted with ease for many different high-order finite difference schemes. The filter coefficients are determined by imposing a required cut-off wavenumber which is a free parameter for the system. The filters incorporate a high-order boundary treatment which enables the closure of the pentadiagonal matrix system and ensures its stable implementation. The overall accuracy of the proposed filter system is proved to be sixth order following grid convergence tests. It is found that a locally non-uniform allocation of cut-off wavenumbers at the boundary nodes (boundary weighting) can enhance the numerical stability of nonlinear solutions especially where a complex geometry is concerned. An optimal value of the boundary weighting factor can be obtained through eigenvalue analysis. The eigenvalue analysis procedure shown in this paper will set an exemplar for the others to customise and optimise the filters for their own use. The new filters are presented in a differential form which has computational benefits in implementation. The accuracy and performance of the proposed filters are demonstrated through a variety of benchmark test cases. [Copyright &y& Elsevier]

Abstract: This paper describes recent studies devoted to the problem of modeling the solid–fluid interaction in partially filled liquid containers. This problem is of much importance for numerous applications, including those in the airspace industry (rockets, satellites), road and naval transportation, and has become in recent years an object of keen interest from researchers. The paper focuses in particular on the sloshing phenomenon and on the numerical approaches used to predict the sloshing wave amplitude, frequency, pressure exerted on the walls and the effect of sloshing on the stability in the container environment. Recent publications devoted to sloshing and fluid–structure interaction are reviewed and the numerical methods used in then are exposed and classified according to the problem formulations employed. They concern primarily finite-elements and finite-differences methods applied to Euler or Lagrangian fluid and solid domains, as well as the smoothed particle method. Issues related to modeling the free-surface of the fluid, fluid–solid interface and to numerical coupling are exposed. Results obtained by various numerical methods are discussed in comparison with experimental results, where possible. Applications of sloshing models in naval, aerospace and other industries are described and discussed. [Copyright &y& Elsevier]

Abstract: This paper provides an efficient numerical method for solving reacting flows of industrial interest in the presence of significant real-gas effects. The method combines a state-of-the-art solver of the Reynolds-averaged Navier–Stokes equations – equipped with the low-Reynolds number turbulence closure – with a combustion flamelet–progress-variable approach. A real-gas model as well as a detailed kinetic scheme are used to generate the flamelet library. The method is tested versus several applications chosen to demonstrate the importance of the real-gas effects and of the kinetic scheme for computing high-pressure combustion. The major contribution of the paper is to provide a single-phase approach which solves turbulent reacting real-gas flows at a computational cost comparable with that of the simulation of a non-reacting flow thanks to the use of the flamelet library. [Copyright &y& Elsevier]

Abstract: In this paper, a novel approach is presented to mechanistically model the dispersion of solid particles due to shear-induced diffusion effect. The model is based on the interfacial force concept, so that it is compatible with the ensemble averaged multifield model of multicomponent flows. Although the new model has been developed with membrane filtration processes in mind, the proposed shear-induced diffusion force formulation can be utilized to model a variety of industrial processes where particulates are present. The model has been verified against the other phenomenological models currently in use. The first part of this paper is concerned with theoretical aspects of model derivation. Then, a numerical analysis is presented to illustrate the application of the new model to dilute liquid/particle two-phase flows in tube membrane systems similar to those that are used for micro- and nano-filtration processes. The numerical simulations have been performed using a state of the art multiphase/multicomponent CFD code, NPHASE [Antal SP, Ettorre SM, Kunz RF, Podowski MZ. Development of a next generation computer code for the prediction of multicomponent multiphase flows. In: International meeting on trends in numerical and physical modeling for industrial multiphase flow, Cargese, France; 2000; Kunz RF, Yu WS, Antal SP, Ettorre SM. An unstructured two-fluid method based on the coupled phasic exchange algorithm. AIAA Paper 2001; 2001:2672]. The numerical consistency of the results of computer calculations have been verified against simplified semi-analytical approximations. [Copyright &y& Elsevier]