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Abstract The paper concerns the analysis of the effects of damping on the linear dynamics of an axially moving non-uniform structure, string with periodically varying mass and damping properties. The string, in particular models transmission chains for drive engines. An expression for the threshold velocity of the string axial motion is determined; if the string moves with a velocity higher than the threshold one, then waves travelling in it are unstable. For a uniform string, the threshold velocity equals to the transverse wave speed. It is shown that pure modulations of the string mass can increase the threshold velocity for waves with certain wavenumbers. By contrast, combined modulations of mass and damping properties lead to reduction of the threshold velocity as compared to the case of the uniform string. And the larger the amplitudes of the modulations, the more pronounced the reduction. This indicates that due to periodic spatial modulations of the string properties, the string dynamics can become unstable even if its axial velocity is considerably lower than the transverse wave speed. Thus, periodic distribution of damping and mass properties can considerably affect design of axially moving structures used in applications. Highlights • An expression for the threshold velocity of the string axial motion is determined. • If the string velocity is higher than the threshold one, its dynamics is unstable. • Periodic modulations of the string mass can increase the threshold velocity. • Combined modulations of mass and damping properties reduce the threshold velocity. • String dynamics can be unstable if its velocity is less than transverse wave speed. [ABSTRACT FROM AUTHOR]

Abstract The numerical implementation of the Taylor Meshless Method (TMM) for solving the two-dimensional Navier–Stokes equations is considered in this paper, where the TMM is a true meshless integration-free method based on Taylor series. The performance of the proposed numerical technique is evaluated by three benchmark tests. In the first case, the exact solution ia a high degree polynomial that permits to check the consistency and high accuracy of the proposed numerical method. Then the comparison with the analytical solution of the Kovasznay flow for the Reynolds number in the range [0,1000] is considered. It turns out that the TMM works well for large values of Reynolds number and it converges rapidly with the degree of Taylor series (p -convergence) and the number of sub-domains (h -convergence). Finally the square lid-driven cavity flow problems for the Reynolds number up to R e = 1000 are solved and excellent agreements with corresponding benchmark solutions are found. [ABSTRACT FROM AUTHOR]

This article elucidates viscoelastic fractional fluid flow along with homogeneous-heterogeneous reactions. Non-integer derivatives are important for the systems having hereditary behavior as they depend on the past conditions along with the local conditions. Viscoelastic fluids keep memory of old deformations and their behavior is related to these deformations. The fractional derivatives are more adequate in predicting the characteristics of viscoelastic fluids than the ordinary derivatives. In this paper we have examined characteristics of fractional homogeneous-heterogeneous reactions with variable concentrations of both the reactant species. Flow is induced by the variable moving surface. Diffusion coefficients of reactants and auto catalyst are of comparable size. For better understanding of hereditary properties, non integer Caputo time derivatives have been incorporated in mathematical formulation of the flow regime. Unsteady motion of a magnetohydrodynamic incompressible viscoelastic fluid is governed by highly nonlinear fractional partial differential equations. Flux conditions are imposed on the chemical species at the boundary. Governing flow equations with suitable initial and boundary conditions have been discretized using finite difference-finite element scheme. Proposed numerical scheme is flexible for the solution of non-linear flow problems. Skin friction coefficients are calculated for fractional viscoelastic model. Flow field is demonstrated for different values of involved parameters. The acquired results revealed that with the increase of fractional exponent α concentration of chemical specie decreases for the final time t = 2 . It is also noted that concentration gradients of chemical specie increase with the increase of α at both the boundaries of flow configuration. In literature no such result exits with non integer Caputo fractional derivatives. Various viscoelastic flows particularly in chemical, plastics and polymer industries can be modeled in a similar manner. [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]

Abstract: In this paper we analyse flow and heat transfer characteristics of nanofluids in natural convection flows in closed cavities. We consider two test cases: natural convection in a three-dimensional differentially heated cavity, and flow around a hotstrip located in two positions within a cavity. Simulations were performed for Rayleigh number values ranging from 103 to 106. Performance of three types of water based nanofluids was compared with pure water and air. Stable suspensions of Cu, Al2O3 and TiO2 solid nanoparticles in water were considered for different volume fractions ranging up to 20%. We present and compare heat flux for all cases and analyse heat transfer enhancement attributed to nanofluids in terms of their enhanced thermal properties and changed flow characteristics. Results show that, using nanofluids, the largest heat transfer enhancements can be achieved in conduction dominated flows as well as that nanofluids increase the three-dimensional character of the flow field. We additionally examine the relationship between vorticity, vorticity flux and heat transfer for flow of nanofluids. The simulations were performed using a three-dimensional boundary element method based flow solver, which has been adapted for the simulation of nanofluids. The numerical algorithm is based on the combination of single domain and subdomain boundary element method, which are used to solve the velocity–vorticity formulation of Navier–Stokes equations. In the paper we present the adaptation of the solver for simulation of nanofluids. Additionally, we developed a dynamic solver accuracy algorithm, which was used to speed up the simulations. [ABSTRACT FROM AUTHOR]

This paper presents a computational framework for model order reduction of viscoelastic fluid flows, with a particular focus on the stabilization of the reduced order model (ROM) and the efficient approximation of non-linear terms appearing in the governing equations. We compare three different stabilization approaches, two of which are based on offline stabilization only and one that uses both offline and online stabilization. Two main techniques for the treatment of non-linear terms are examined and compared: the discrete empirical interpolation method, and a reduced quadrature method based on a sparse recovery technique. Numerical experiments are conducted on two benchmark flows such as the flow past a sphere and the 4:1 contraction flow problem. We show that significant speedups can be achieved using offline streamline upwind Petrov–Galerkin stabilization together with hyper-reduction. We also discuss the potential accuracy losses of the ROM that could result from mesh-related issues of the full-order model (FOM) and propose possible remedies. • The governing equations are presented in both full order model and reduced order model. • Construction of reduced bases of the unknown field variables are discussed. • Stabilization of the governing equations are discussed in both FOM and ROM. • Hyper reduction methods are reviewed and introduced for the treatment of non-linear terms. • Computational performance is evaluated. [ABSTRACT FROM AUTHOR]

Zapdos is an open-source finite element plasma fluid solver based on the MOOSE multiphysics framework. This paper outlines Zapdos verification, benchmarking, and validation efforts for 1D and 2D RF capacitively-coupled plasma discharge models for mid-range pressures (0.1 - 1 Torr). The verification process involved using the method of manufactured solutions to assess Zapdos spatial and temporal error convergence. L 2 errors ranged from 10 − 2 to 10 − 4 , while the convergence's slope were in agreement with the predicted slopes for the tested variable and time integration orders. The benchmarking process involved comparisons to previously results from the validated finite element code, LSODI [1–3]. These works included 1D and 2D simulations for a range of plasma parameters (densities, temperatures, voltage, etc.). For the 1D cases, Zapdos and LSODI results were in very good agreement. In the 2D cases, variable behaviors matched, with slight discrepancies in peak values. The validation process involved comparisons to experimental works including electron density measurements by microwave interferometry [4] and metastable density measurements by planar laser-induced fluorescence imaging [5]. Results shown reasonable agreement at higher pressure, with results starting to diverge at low pressures. Probable causes for this diverges are the limitation of the fluid assumption for plasmas at low pressure, or the need for more robust boundary conditions. Overall, Zapdos shown reasonable results for the verification, benchmarking, and validation efforts, and Zapdos can be downloaded at https://github.com/shannon-lab/zapdos. Program Title: Zapdos CPC Library link to program files: https://doi.org/10.17632/j76jr9m66p.1 Developer's repository link: https://github.com/shannon-lab/zapdos Licensing provisions: LGPL-2.1 Programming language: C++, Python Supplementary material: shannon-lab.github.io/zapdos Nature of problem: For the plasma computational community, multiphysics packages are needed for the highly couple physics seen in plasma problems (e.g. chemistry, fluid flow, heat transfer, electromagnetic, etc.). One limiting factor for these types of computational research is the high cost to purchase the licenses needed for established multiphysics packages, such as COMSOL. An additional problem that can arise is the limited ability to add new physics to these existing frameworks, in such a way that new physics can be easily coupled to current models. For any new software that wants to tackle these problems, the question of verification and validation for these codes needs to be addressed. Solution method: Zapdos is an open-source finite element plasma fluid solver based on the MOOSE multiphysics framework. MOOSE (Multiphysics Object Oriented Simulation Environment) solves highly nonlinear, tightly coupled sets of partial differential equations (PDEs) and houses multiple physics applications that can be easily coupled together. Zapdos, along with the MOOSE ecosystem, is all free, open-source, and completing customizable with no black box components. Zapdos has gone through verification and validation for applications common in the plasma computational community. Additional comments including restrictions and unusual features: Zapdos, along with MOOSE and other MOOSE applications, require an Unix based operating system. • Zapdos is an open-source finite element plasma fluid solver on the MOOSE framework. • Verification and Validation for RF capacitively-coupled plasma discharges. • Modular approach to Method of Manufactured Solutions and convergence studies. • 1D and 2D benchmarking comparisons and experimental validation. • Sample code and input file examples. [ABSTRACT FROM AUTHOR]

This paper is devoted to a well-posedness analysis of elliptic variational–hemivariational inequalities in Banach spaces. The differential operator associated with the variational–hemivariational inequality is assumed to be strongly monotone of a general order, in contrast to that in the majority of existing references on this subject where the differential operator is assumed to be strongly monotone of order 2. Moreover, the solution existence is proved with an approach more accessible to applied mathematicians and engineers, instead of through an abstract surjectivity result for pseudomonotone operators in existing references. Equivalent minimization principles are established for certain variational–hemivariational inequalities, which are valuable for developing efficient numerical algorithms. The theoretical results are applied to the analysis of a mixed hemivariational inequality in the study of a generalized Newtonian fluid flow problem involving a nonsmooth slip boundary condition of friction type. Existence and uniqueness of both the velocity and pressure unknowns are shown for the mixed hemivariational inequalities. • Well-posedness of VHIs with strongly monotone operators of a general order. • The solution existence is proved with a more accessible approach. • Equivalent minimization principles are established for certain VHIs. • Existence and uniqueness of both the velocity and pressure unknowns are shown. [ABSTRACT FROM AUTHOR]

A numerical model is presented in this paper to better describe the cavitated fluid flow phenomena in liquid-lubricated Asymmetrical Herringbone Grooved Journal Bearings (HGJBs). An effective "follow the groove" grid transformation method is used in the present study to capture all the groove boundaries. A singularity at the groove edges is avoided with this approach. Symmetrical groove patterns as well as asymmetrical groove patterns can be accurately computed with the proposed method. The difficult problem of abrupt changes of oil film thickness in the liquid-lubricated HGJB physical domain is modeled here through a series expansion approach. Results are comparable with available experimental and known numerical data from other investigators. Cavitation footprints, pressure distributions and their corresponding load characteristics are presented in this study. Effects of the critical transitional flow phenomena on the performance of the asymmetrical HGJBs are also determined through the present study. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to simulate the dendritic growth in Stokes flow by iteratively coupling a domain and boundary type meshless method. Design/methodology/approach: A preconditioned phase-field model for dendritic solidification of a pure supercooled melt is solved by the strong-form space-time adaptive approach based on dynamic quadtree domain decomposition. The domain-type space discretisation relies on monomial augmented polyharmonic splines interpolation. The forward Euler scheme is used for time evolution. The boundary-type meshless method solves the Stokes flow around the dendrite based on the collocation of the moving and fixed flow boundaries with the regularised Stokes flow fundamental solution. Both approaches are iteratively coupled at the moving solid–liquid interface. The solution procedure ensures computationally efficient and accurate calculations. The novel approach is numerically implemented for a 2D case. Findings: The solution procedure reflects the advantages of both meshless methods. Domain one is not sensitive to the dendrite orientation and boundary one reduces the dimensionality of the flow field solution. The procedure results agree well with the reference results obtained by the classical numerical methods. Directions for selecting the appropriate free parameters which yield the highest accuracy and computational efficiency are presented. Originality/value: A combination of boundary- and domain-type meshless methods is used to simulate dendritic solidification with the influence of fluid flow efficiently. [ABSTRACT FROM AUTHOR]

The article presents a personal narrative of his experience of developing vortex fluidic device (VFD).

In this paper, the generalized finite difference method (GFDM) combined with the Newton–Raphson method is proposed to accurately and efficiently simulate the steady-state double-diffusive natural convection in parallelogrammic enclosures filled with fluid-saturated porous media. The natural convection in fluid-saturated porous media, which is interesting in regard to the heat-transferring range, involves different physical compositions to affect the fluid flow. For the mathematical formulations of the natural convention, the governing equations are a system of highly-nonlinear partial differential equations, so the approximate solutions for the natural convention mainly depend on a suitable numerical scheme. In this study, the GFDM, a newly-developed meshless method, is adopted for the spatial discretization of the non-linear governing equations, since it can avoid setting up the mesh in the computational domain and implementing the numerical quadrature. The localization of the GFDM will result in a sparse system, while the derivatives at each node can be expressed as linear combinations of nearby function values with different weighting coefficients. After a system of nonlinear algebraic equations is yielded by the spatial discretization of the GFDM, the two-steps Newton–Raphson method is adopted to efficiently solve this resultant sparse system owing to the localization of the GFDM. Three numerical examples are presented to demonstrate the applicability and stability of the proposed meshless numerical scheme. Besides, the numerical results are compared with other solutions to show the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Several dispersion relation-preserving (DRP) spatially central discretizations are considered as the base scheme in the framework of the Yee & Sjögreen low dissipative nonlinear filter approach. In addition, the nonlinear filter of Yee & Sjögreen with shock-capturing and long time integration capabilities is used to replace the standard DRP linear filter for both smooth flows and flows containing discontinuities. DRP schemes for computational aeroacoustics (CAA) focus on dispersion error consideration for long time linear wave propagation rather than the formal order of accuracy of the scheme. The resulting DRP schemes usually have wider grid stencils and increased CPU operations count compared with standard central schemes of the same formal order of accuracy. For discontinuous initial data and long time wave propagation of smooth acoustic waves, various space and time DRP linear filter are needed. For acoustic waves interacting with shocks and turbulence induced noise, DRP schemes with linear filters alone usually are not capable of simulating such flows. The investigation presented in this paper is focused on the possible gain in efficiency and accuracy by spatial DRP schemes over standard central schemes having the same grid stencil width for general direct numerical simulations (DNS) and large eddy simulations (LES) of compressible flows. Representative test cases for both smooth flows and problems containing discontinuities for 3D DNS of compressible gas dynamics are included. [ABSTRACT FROM AUTHOR]

Boundary slip phenomenon has been widely studied for microscale gas flow in recent years. However, researches on this topic for liquid flow are still rare. Boundary slip of liquid flow is caused by roughness and micro bubbles, while that of gas flow is caused by rarefied effect. Despite this difference, researchers found that some slip boundary conditions for gas flow can also be applied to liquid flow, except the different way of treating accommodation coefficients. Currently, a measurable physical parameter, slip length, is widely used for liquid flow, which can be obtained through experiential methods. If the relationship between the slip length and the accommodation coefficients can be found theoretically, these slip boundary conditions for liquid flow will be powerful tools to research slip related flow characteristics, for example, drag reduction with superhydrophobic surface. Based on the Navier slip model, this paper deducts the relationship between the accommodation coefficients and the slip length with the half-way and the modified slip boundary conditions, under the framework of the lattice Boltzmann method (LBM). The effectiveness of the proposed slip boundary conditions are verified with the Couette flow, the Poesueille flow, the water Cu nanofluid flow, and the 2-D Womersley flow. Results indicate that these boundary conditions are suitable for both linear and non-linear liquid flow. [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]

Diagenesis of Upper Carboniferous foreland shelf rocks in southeastern Kansas took place at temperatures as high as 100-150° C at a depth of less than 2 km. High temperatures are the result of the long distance (hundreds of kilometers) advection of groundwater related to collisional orogeny in the Ouachita tectonic belt to the south. Orogenic activity in the Ouachita area was broadly Late Carboniferous, equivalent to the Variscan activity of Europe. Mississippi Valley-type Pb-Zn deposits and oil and gas fields in the US midcontinent and elsewhere are commonly attributed to regional groundwater flow resulting from such collisional events. This paper describes the diagenesis and thermal effects in sandstone and limestone of Upper Carboniferous siliciclastic and limestone-shale cyclothems, the purported confining layer of a supposed regional aquifer. Diagenesis took place in early, intermediate, and late stages. Many intermediate and late stage events in the sandstones have equivalents in the limestones, suggesting that the causes were regional. The sandstone paragenesis includes siderite cement (early stage), quartz overgrowths (intermediate stage), dissolution of feldspar and carbonates, followed by minor Fe calcite, pore-filling kaolinite and sub-poikilotopic Ca ankerite (late stage). The limestone paragenesis includes calcite cement (early stage); megaquartz, chalcedony, and Fe calcite spar (intermediate stage); and dissolution, Ca-Fe dolomite and kaolinite (late stage). The R value of vitrinite shows a regional average of 0.6-0.7%; Rock-Eval T suggests a comparable degree of organic maturity. The T of aqueous fluid inclusions in late stage Ca-Fe-Mg carbonates ranges from 90 to 160° and T indicates very saline water (>200000 ppm NaCl equivalent); δO suggests that the water is of basinal origin. Local warm spots have higher R, T, and T. The results constrain numerical models of regional fluid migration, which is widely viewed as an artesian flow from recharge areas in the Ouachita belt across the foreland basin onto the foreland shelf area. Such models must account for heating effects that extend at least 500 km from the orogenic front and affect both supposed aquifer beds and the overlying supposed confining layer. Warm spots indicate either more rapid or more prolonged flow locally. T and T data show the highest temperatures coincided with high salinity fluids. [ABSTRACT FROM AUTHOR]

The IV bag wringer of claim 11, further comprising: a first side screw rotatably coupled to a first threaded opening in the first linear slide bearing; and a second side screw rotatably coupled to a second threaded opening in the second linear slide bearing, wherein rotation of the first and second side screws is configured to slidably move the first and second linear slide bearings along the first and second slider guides. The IV bag wringer of claim 1, further comprising a restraining member configured to hold the IV bag wringer in an unactuated state relative to the IV fluid bag. The IV bag wringer of claim 1, wherein at least one roller assembly is adjustably coupled to the frame, the adjustably coupled roller assembly configured to adjust a size of the gap between the opposing rollers based on an adjusted position. [Extracted from the article]

• Fluid flows must depend on the geometries of given domains or irregularities of given data. In particular, when the datum has a jump discontinuity at a point, a curve started at the point can be generated into the domain and the jump discontinuity is propagated along the curve. The curve is directed by the fluid velocity vector. So the pressure gradient given in the momentum equations is not well-defined across the curve. • Recently we have shown that, when the inflow boundary data has a jump, there is a curve contained in the domain such that the fluid flows have jump there. By constructing a lifting vector field for the pressure jump value on the curve we decompose the solution into the jump part, the contact singularity part and the smoother one. In fact the solutions of the nonlinear compressible Stokes system are (0.1) u = K + Φ + w , p = p b + k + τ + σ , where p b has a jump discontinuity on inflow boundary, the pair (K , k) denotes the jump part, (Φ , τ) the contact singularity and (w , σ) the smoother part. The contact singular part is due to the intersection of the interface curve to the boundary of the domain. It is assumed that we have two contact points, denoted by a j , j = 1 , 2. • We call the curve the interface or jump curve and denote by C. Since the curve is directed by the velocity vector it is important to have a precise structure of the velocity vector. • In this paper we design a finite element numerical scheme based on the decomposition and try to address and confirm the important roles of each component in the decomposition numerically. It has been shown in [8] that the solutions of compressible Stokes flows with inflow jump condition can be decomposed into the jump discontinuity part (due to the pressure jump) plus the contact singularity (to the boundary) plus the smoother one, which is twice differentiable. In this paper we design a numerical scheme of each part in the decomposition and numerically demonstrate its essential role for capturing the jump discontinuity behaviors of the solutions. Several numerical simulations are presented, describing the critical role of each part. It is thought that such algorithm is new in constructing the jump discontinuity solutions. [ABSTRACT FROM AUTHOR]

The flow field around the rectangular cylinder with aspect ratio 5:1 has been widely investigated in recent literature as a prototype of reattached flow around elongated bluff bodies like bridge decks and high rise buildings. Due to the technical importance of such flows, many research works have been proposed aiming at studying the accuracy of available simulation techniques in reproducing the flow organization. When Large Eddy Simulations (LES) are considered, to the authors’ knowledge, the proposed contributions focused on perfectly smooth inlet conditions which, indeed, represent more an exception than a rule in Computational Wind Engineering. In the present paper, LES are performed aiming at reproducing the modifications occurring in the flow when turbulent inflow conditions are adopted. In order to synthetically produce the unsteady inlet condition, a divergence-free and spatially correlated fluctuations field is generated by means of the Modified Discretizing and Synthesizing Random Flow Generator technique. The obtained synthetic fluctuations are imposed in the computational domain by modifying the velocity-pressure coupling algorithm in order to avoid nonphysical pressure fluctuations. Two configurations, corresponding to mild and strong incoming turbulence levels, are investigated highlighting the role played by the spanwise domain size. Results are compared to experimental data showing good agreement between experiments and numerical simulations. [ABSTRACT FROM AUTHOR]

The present paper addresses the issue of the strong dependency of eddy-resolving simulations for turbulent flows on the employed inflow conditions. Thus, the objective of this study is to analyze the influence of the inflow conditions on the external wall-bounded flow past the SD7003 airfoil and more precisely on the form and size of the laminar separation bubble. Motivated by the typically coarse resolution of the inlet region of the computational domain used for hybrid simulations, the synthetic turbulence is introduced within the flow field by a flexible source term treatment. The generated turbulent fluctuations are taken into account in the momentum equation by source terms and hence allow a shift from the inlet to a finer resolved region, where the damping of small structures due to the grid resolution is negligible. To provide a proper formulation of a synthetic turbulence inflow generator (STIG), the digital filter concept of Klein et al. (J. Comp. Phys. 186, 652–665, 2003) is merged with a large-eddy simulation (LES) as well as a hybrid LES-URANS method. The synthetically generated velocity fluctuations are distributed in an area of influence which is in accordance with the digital filter concept of the STIG. An automatic calculation of the dimension of the influence region is ensured by the employment of the integral scales which are used during the generation of the synthetic turbulence inflow generator inflow. The definition of the required input quantities for the STIG in case of the flow past a SD7003 airfoil at Re c = 60 , 000 and an angle of attack α = 4 ∘ are based on experimental data including a turbulence intensity of TI = 0.28%. Due to separation, transition and subsequent reattachment this is a demanding test case in which the shape and the size of the separation bubble strongly depends on the oncoming turbulence. The reference velocity profiles of the experimental measurements are compared with a wall-resolved LES and hybrid simulations performed on two grids with a coarser resolution. The evaluation of the results of the simulations applying the STIG and without turbulence intensity showed an improved level of agreement between the STIG based simulations and the experiment. Moreover, the turbulence intensity is varied to understand the behavior of the LSB in more detail. [ABSTRACT FROM AUTHOR]

Inspired by the pectoral flippers of the humpback whale, the use of spanwise waviness in the leading edge has been considered in the literature as a possible way of improving the aerodynamic performance of wings. In this paper, we present an investigation based on direct numerical simulations of the flow around infinite wavy wings with a NACA0012 profile, at a Reynolds number R e = 1000 . The simulations were carried out using the Spectral/hp Element Method, with a coordinate system transformation employed to treat the waviness of the wing. Several combinations of wavelength and amplitude were considered, showing that for this value of Re the waviness leads to a reduction in the lift-to-drag ratio ( L / D ), associated with a suppression of the fluctuating lift coefficient. These changes are associated with a regime where the flow remains attached behind the peaks of the leading edge while there are distinct regions of flow separation behind the troughs, and a physical mechanism explaining this behaviour is proposed. [ABSTRACT FROM AUTHOR]

Single-phase two-dimensional flow past a circular cylinder intersecting, or close to, a free surface at a Reynolds number of 180 is numerically investigated in this paper series using the Smoothed Particle Hydrodynamics (SPH) method. The wake behavior for Froude numbers between 0.3 and 2.0, based on the diameter, and for submergence-diameter ratios between − 0.5 and 2.5 is examined. This range significantly extends existing literature on the topic. Vorticity shed by the cylinder, vortex generation due to free-surface breaking, and mixing processes are discussed. Regarding the submergence dependence, it has been found that for small gap ratios, the classical von Kármán vortex shedding from the cylinder does not take place. In turn, vortex shedding originates from wave-breaking at the free surface, occurring simultaneously with the transport of free-surface fluid elements into the bulk of the fluid. It has been also found that for even smaller depth ratios, a vorticity layer remains spatially localized between the cylinder and the free surface, and a large stagnation recirculating area develops behind the cylinder. In some of these cases, the whole mass of fluid in that area eventually gets detached after several shedding cycles and it is advected downstream. According to the authors’ knowledge, this is a previously unreported form of wake instability. It has been also found that as the Froude number is increased, the classical von Kármán vortex street shed from the cylinder is blocked only to be recovered at very high Froude numbers, in agreement with linear stability predictions. Regarding the challenging and not previously investigated half-submerged configuration, flows in which the cylinder acts as a barrier, flows with alternation of dry and wet cylinder top surface, and flows with cavities have been described. [ABSTRACT FROM AUTHOR]

In this paper we present approaches that address two issues that can occur when the level-set method is used to simulate two-fluid flows in engineering practice. The first issue concerns regularizing the Heaviside function on arbitrary meshes. We show that the regularized Heaviside function can be non-smooth on non-uniform meshes. Alternative regularizing definitions that are indeed smooth and monotonic, are introduced. These new definitions lead to smooth Heaviside functions by taking the changing local meshsize into account. The second issue is the computational cost and fragility caused by the necessity of redistancing the level-set field. In [1, 2] it is shown that strongly coupling the level-set convection with the flow solver provides robustness and potentially efficiency and accuracy advantages. The next step would be to include redistancing within the strong coupling part of the algorithm. The computational cost of current redistancing procedure prohibit this. Four alternative approaches for circumventing the expensive redistancing step are proposed. This should facilitate a fully coupled level-set approach. Some benchmark cases demonstrate the efficacy of the proposed approaches. These includes the standard test case of the vortex in a box. Based on these results the most favourable redistancing approach is selected. [ABSTRACT FROM AUTHOR]

Finite sized particles exhibit complex dynamics that differ from that of the underlying fluid flow. These dynamics such as chaotic motion, size dependent clustering and separation can have important consequences in many natural and engineered settings. Though fluid streamlines are global attractors for the inertial particles, regions of local instability can exist where the inertial particle can move away from the fluid streamlines. Identifying and manipulating the location of the so called stable and unstable regions in the fluid flow can find important applications in microfluidics. Research in the last two decades has identified analytical criteria that can partition the fluid domain into locally stable and unstable regions. In this paper, we identify two new mechanisms by which neutrally buoyant inertial particles could exhibit globally stable dynamics in the regions of the fluid flow that are thought to be locally unstable and demonstrate this with examples. The examples we use are restricted to the simpler case of time independent fluid flows. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this article is to numerically investigate the effect of casting speed on the fluid flow, solidification and inclusion motion under the influence of electromagnetic stirring (EMS) in the bloom caster mold with bifurcated submerged entry nozzle (SEN). Design/methodology/approach: The electromagnetic field obtained by solving Maxwell's equation is coupled with the fluid flow, solidification and discrete phase model using the in-house user-defined functions. An enthalpy porosity approach and Lagrangian approach are applied for the solidification analysis and non-metallic inclusions motion tracking, respectively. Findings: Investigation shows that the casting speed and EMS significantly affect the steel flow, solidification and inclusion behavior inside the mold. Investigations are being conducted into the complex interplay between the induced flow and the SEN's inertial impinging jet. In low and medium casting speeds, the application of EMS significantly increases the inclusion removal rate. Inclusion removal is studied for its different size and density and further effect of EMS is also reported on cluster formation and distribution of inclusion in the domain. Practical implications: The model may be used to optimize the process parameter (casting speed and EMS) to improve the casting quality of steel by removing the impurities. Originality/value: The effect of casting speed on the solidification and inclusion behavior under the influence of time-varying EMS in bloom caster mold with bifurcated nozzle has not been investigated yet. The findings may assist the steelmakers in improving the casting quality. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to obtain both the numerical and asymptotic solutions of the unsteady mixed convection flow and heat transfer over an expanding or contracting cylinder which is placed vertically. Design/methodology/approach: Solutions of the governing ordinary (similarity) differential equations for the fluid flow and temperature field are obtained using the function bvp4c from MATLAB. The problem involves the Prandtl number σ, the mixed convection parameter λ and unsteadiness parameter S that characterize an expanding or contracting cylinder. This solution approach is capable of producing multiple solutions once the necessary assumptions are provided. Findings: It is found that solutions exist for all negative values of S, expanding cylinder, and only for small positive values of S, contracting cylinder. Further, more than one solution is observed; numerical computation shows that the critical point of S becomes singular as λ approaching zero. For the case of expanding cylinder, the mixed convection parameter has a significant effect on both the flow and heat transfer characteristics. Asymptotic analysis also shows that when σ is large, dual solutions exist for some values of S and λ. Originality/value: The present results are new and original for the study of the unsteady mixed convection flow and heat transfer over an expanding/contracting cylinder where numerical solutions are obtained for representative values of the involved parameters. Asymptotic solutions for large λ and large σ are derived. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann flux solver (LBFS), first introduced by Shu et al. (2014) on structured meshes, allows fluid flow problems to be solved on unstructured meshes discretised by the finite volume method. The solver calculates the macroscopic fluxes at the cell interfaces from a local reconstruction of the lattice Boltzmann solution. In this paper the LBFS is extended to three-dimensional unstructured hexahedral meshes and a preconditioned lattice Boltzmann flux solver (PLBFS) is presented. The PLBFS involves applying the preconditioning technique proposed by Guo (2004) to the LBFS and is achieved by modifying the equilibrium distribution function used to calculate the macroscopic fluxes at the cell interface. When the PLBFS is applied to steady flow problems, it is shown that convergence is significantly accelerated and the accuracy of predictions with unstructured grids is greatly improved when compared to the LBFS. This paper also introduces a strategy for choosing the optimal value of preconditioning factor with unstructured hexahedral meshes. [ABSTRACT FROM AUTHOR]

ENATE (E nhanced N umerical A pproximation of a T ransport E quation) is a high-order exponential scheme for convection–diffusion problems, such as those that govern the transport of fluid properties in a flow field. The scheme was intended to be employed in fluid-related transport equations, although it can be used for any inhomogeneous second-order ordinary differential equation. The value of a variable ϕ at a generic point is related to those of adjacent nodes via an algebraic equation. Thus, a three-point stencil is associated to each node. The coefficients of this equation contain integrals of some fluid and flow parameters. One important property is that the scheme allows to obtain a machine-accurate solution of an inhomogeneous transport equation if these integrals can be obtained analytically. As the scheme is essentially one-dimensional, getting the machine-accurate solution of multidimensional problems is not guaranteed even in cases where ENATE integrals are analytic along each coordinate. In this regard the paper presents a simple way of getting solutions in multidimensional problems while still using the one-dimensional formulation. Moreover, if the problem is such that the solution is machine-accurate in the one-dimensional problem along coordinate lines, it will also be for the multidimensional domain. Two different methods of evaluating those terms that come out of the discretization will be explained and compared in various cases. • Development of ENATE for computing steady-state 2D problems and unsteady 1D problems. • Two splitting approaches are considered for the extension: FaP and REMEDIES. • Accuracy and CPU time are compared in FaP and REMEDIES for wide Péclet numbers. • REMEDIES is a viable alternative to FaP, reducing CPU time and increasing accuracy. [ABSTRACT FROM AUTHOR]

This paper aims to establish a novel and efficient topology optimization method for the thermal-fluid. To adaptively design the fluid–solid coupling structure and make the objective energy to dissipate, the proposed method considers several constraints, such as the volume conservation, inlet and outlet flow velocity field and fluid–solid boundary constraints. The governing system includes the phase-field model, the steady state Darcy equation and the heat transfer equation. Under the constraints of multiple physical fields, we prove the existence of minimal solutions to the optimization problem. We use a Crank–Nicolson (CN) type scheme to discretize the governing system. The multigrid method is used to solve the resulting system of discrete equations. We prove the boundedness and unconditional stability of the original energy, which implies that a large time step can be used. The proposed discrete system is both spatially and temporally second-order accurate. Various computational tests have been performed to demonstrate that the numerical approach is efficient in designing the complicated structures of thermal fluid flows. • An unconditionally energy stable topology optimization method has been established for thermal-fluid. • The minimal solution of the optimization problem has been proved to exist. • The proposed scheme has second-order temporal and spatial accuracy. • Various tests were implemented to show the robustness and efficiency of our method. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate partial magnetic source (MS) effect on natural convection (NC) flow of a ferrofluid flow in a cavity with sinusoidally heated vertical walls. The combination of ferrohydrodynamics and magnetohydrodynamics due to the variable magnetic field (MF) and magnetite nanoparticles in one part of the cavity, and the classical NC in the other part of the cavity are concerned. Design/methodology/approach: The dimensionless equations in stream function-vorticity form are numerically solved by radial basis functions (RBF) based collocation method. Findings: A remarkable change in fluid flow and heat transfer is noted if the MS location is close to the left sinusoidally heated wall. In particular, the average Nusselt number is the smallest for the middle centered partial MF through the left wall at a large Hartmann number. Research limitations/implications: RBF collocation approach is limited to small geometries due to the obtained solution globally in the entire domain of the problem. Practical implications: If the partial restriction of the effect of MF is done in real life, it would be a control parameter at some required/requested areas of the concerned problem. Social implications: This is a physical problem. Originality/value: If the proposed idea of partial variable MF is able to be applied to a system in real life, it would be a good controller on fluid flow and heat transfer. RBF-based methods are also alternative numerical procedures to solve heat transfer and fluid flow problems. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the two-dimensional unsteady inclined stagnation point flow and thermal transmission of Maxwell fluid on oscillating stretched/contracted plates. First, based on the momentum equation at infinity, pressure field is modified by solving first-order differential equation. Meanwhile, thermal relaxation characteristic of fluid is described by Cattaneo–Christov thermal diffusion model. Design/methodology/approach: Highly coupled model equations are transformed into simpler partial differential equations (PDE) via appropriate dimensionless variables. The approximate analytical solutions of unsteady inclined stagnation point flow on oscillating stretched and contracted plates are acquired by homotopy analysis method for the first time, to the best of the authors' knowledge. Findings: Results indicate that because of tensile state of plate, streamline near stagnation point disperses to both sides with stagnation point as center, while in the case of shrinking plate, streamline near stagnation point is concentrated near stagnation point. The enhancement of velocity ratio parameter leads to increasing of pressure variation rate, which promotes flow of fluid. In tensile state, surface friction coefficient on both sides of stagnation point has opposite symbols; when the plate is in shrinkage state, there is reflux near the right side of the stagnation point. In addition, although the addition of unsteady parameters and thermal relaxation parameters reduce heat transfer efficiency of fluid, heat transfer of fluid near the plate can also be enhanced by considering thermal relaxation effect when plate shrinks. Originality/value: First, approximate analytical solutions of unsteady inclined stagnation point flow on oscillating stretched and contracted plates are researched, respectively. Second, pressure field is further modified. Finally, based on this, thermal relaxation characteristic of fluid is described by Cattaneo–Christov thermal diffusion model. [ABSTRACT FROM AUTHOR]

The two-dimensional flow generated by a local density perturbation (fully mixed region) in stratified fluid is considered. In order to describe accurately the sharp discontinuity in density at the edge of the mixed region, monotone schemes of high order of approximation are required. Although a great variety of methods have been developed during the last decades, there remains the question of which method is the best. This present paper deals with the numerical treatment of the advective terms in the Navier–Stokes equations in the Oberbeck–Boussinesq approximation. Comparisons are made between the upwind scheme, flux-limiter schemes, namely Minmod, Superbee, van Leer and monotonized centred (MC), monotone adaptive stencil schemes, namely ENO3 and SMIF, and the weighted stencil scheme WENO5. We used the laboratory experimental data of Wu as a benchmark test to compare the performance of the various numerical approaches. We found that the flux limiter schemes have the smallest numerical diffusion. On the other hand, the WENO5 scheme describes the variation of the width of the collapsing region over time most accurately. All considered schemes give realistic patterns of internal gravity waves generated by the collapsing region. [ABSTRACT FROM AUTHOR]

This paper presents a modified incompressible smoothed particle hydrodynamics (MISPH) method for fluid-porous media interaction problems. Navier–Stokes and Brinkman Equations are considered for modeling the fluid flow outside and inside porous media. The MISPH method utilizes a truly incompressible divergence free velocity formulation. The equations are solved by using a robust two-step semi-implicit exact projection method. Turbulence stresses are evaluated by using an semi-analytical Smagorinsky model. The representative volume of the particles changes with the porosity. Interface conditions are imposed implicitly by using Darcy velocity and modified Pressure Poisson Equation (PPE) with porosity in the source/sink term. Impermeable boundary conditions are simulated with fixed ghost particles. The model is validated by using existing experimental results of dambreak flow through a homogeneous porous block in a wet bed. Simulation results show good agreement with experimental data. An application to heterogeneous porous media demonstrates the applicability and adaptability of the proposed framework. The numerical model is capable of efficiently capturing the interaction of fluid in porous and nonporous media. [ABSTRACT FROM AUTHOR]

The plastic response of metals is determined by the collective, coarse-grained dynamics of dislocations, rather than by the dynamics of individual dislocations. The evolution equations at both levels are quite different, for example considering their dependence on the applied mechanical load. On the one hand, the relation between the configurational force and dislocation velocity for individual dislocations is linear. On the other hand, in phenomenological crystal plasticity models, the relation between load and plastic slip is highly non-linear and often taken of power-law form. In this work, it is shown that this difference is justified and a consequence of emergent effects. Previously, an expression for the macroscopic dislocation flux was derived by systematic coarse graining ( Kooiman et al., 2015 ). This expression has been evaluated numerically in this paper. The resulting relation between dislocation flux and applied mechanical load is found to be of power-law form with an exponent 3.7, while the underlying Discrete Dislocation Dynamics has a linear flux–load relation. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration of a three-dimensional flexible tube is one of the key problems to be considered in many engineering situations. This paper aims to investigate the nonlinear dynamic behaviors and response characteristics of a three-dimensional tube under turbulent flow. The three-dimensional unsteady, viscous, incompressible Navier–Stokes equation and LES turbulence model are solved with the finite volume approach, and the dynamic equilibrium equations are discretized by the finite element theory. A three-dimensional fully coupled numerical model for vortex-induced vibration of flexible tube is proposed. The model realized the fluid–structure interaction with solving the fluid flow and the structure vibration simultaneously. Based on this model, Response regimes, trajectory, phase difference, fluid force coefficient and vortex shedding frequency are obtained. The nonlinear phenomena of lock-in, phase-switch are captured successfully. Meanwhile, the limit cycle, bifurcation of lift coefficient and displacement are analyzed using phase portrait and Poincare section. The results reveal that, a quasi-upper branch occurs in the present fluid-flexible tube coupling system with high mass-damping and low mass ratio. There is no bifurcation of lift coefficient and lateral displacement occurred in the three-dimensional flexible tube submitted to uniform turbulent flow. [ABSTRACT FROM AUTHOR]

The applicability of immersed boundary method (IBM) in solving flow over complex and moving geometries is often restricted due to the computational overheads associated with the dynamic identification of immersed nodes and the high ratio of solid to fluid nodes. Furthermore, improper mass conservation and the unphysical pressure fluctuations result in large errors in IBM based flow predictions. Earlier attempts to overcome these issues were usually mathematically involved and computationally expensive. In the present paper, a simple and robust IBM implementation has been demonstrated which addresses these issues. The present method preserves the simplicity of sharp interface immersed boundary method and hence avoids complex coding logistics. This method uses a dynamic search algorithm for tagging of the immersed nodes and reduces the computational overheads. Mass conservation is ensured in the intercepted cells through a hybrid SOLA–MAC algorithm. The proposed algorithm iteratively satisfies the mass conservation equation in the intercepted cell and also eliminates spurious fluctuations in the temporal behavior of pressure. An overall second order accuracy is maintained in the discretization and interpolation schemes. The effectiveness and accuracy of the present scheme in handling the mass loss and spurious pressure fluctuation are demonstrated through a number of test cases. Comparisons are made with available experimental and numerical data for different external and internal flow problems. [ABSTRACT FROM AUTHOR]

Purpose – The knowledge about the heat transfer and flow field in the ribbed internal passage is particularly important in industrial and engineering applications. The purpose of this paper is to identify and analyze the performance of the constrained large-eddy simulation (CLES) method in predicting the fully developed turbulent flow and heat transfer in a stationary periodic square duct with two-side ribbed walls. Design/methodology/approach – The rib height-to-duct hydraulic diameter ratio is 0.1 and the rib pitch-to-height ratio is 9. The bulk Reynolds number is set to 30,000, and the bulk Mach number of the flow is chosen as 0.1 in order to keep the flow almost incompressible. The CLES calculated results are thoroughly assessed in comparison with the detached-eddy simulation (DES) and traditional large-eddy simulation (LES) methods in the light of the experimentally measured data. Findings – It is manifested that the CLES approach can predict both aerodynamic and thermodynamic quantities more accurately than the DES and traditional LES methods. Originality/value – This is the first time for the CLES method to be applied to simulation of heat and fluid flow in this widely used geometry. [ABSTRACT FROM AUTHOR]

The recently proposed discrete unified gas kinetic scheme (DUGKS) is a finite volume method for multiscale flow computations with asymptotic preserving property. The solution of the Boltzmann model equation is directly used for the construction of numerical flux and makes the scheme applicable in all flow regimes. In previous applications of the DUGKS, structured meshes have been mostly employed, which may have difficulties for problems with complex geometries. In this paper we will extend the DUGKS to unstructured meshes, with the implementation of computational fluid dynamics techniques to the DUGKS. Several test cases, i.e., the cavity flow ranging from continuum to free molecular regimes, a multiscale flow problem between two connected cavities with large pressure and density variations, high speed flows past multiple cylinders in slip and transitional regimes, and an impulsive start problem are performed. The results are compared with the well-defined Direct Simulation Monte Carlo (DSMC) or Navier–Stokes (NS) solutions in their applicable regimes. The numerical results demonstrate the effectiveness of the proposed DUGKS for the study of multiscale flow problems. [ABSTRACT FROM AUTHOR]

The paper presents a solution algorithm for variable density non-isothermal flows based on a high-order compact difference approximation combined with the projection method formulated on half-staggered meshes. In contrast to full-staggered grid arrangement, with the pressure and all scalar variables located in the cell centers, we shift only the pressure nodes while we keep the scalars and velocity components in the same nodes. This greatly simplifies the solution procedure as the interpolation between the nodes takes place only within the projection method. Derivative approximations and interpolation formulas are discretized using the high-order compact difference schemes up to 10th order in the central nodes and third/fourth order schemes near domain boundaries. The proposed algorithm is first verified in natural convection problems in square and rectangular wall bounded cavities for Rayleigh numbers Ra = 3.4 × 10 5 and Ra = 1.0 × 10 6 with maximal density ratio equals nine. The results are compared with published data for both steady and unsteady flow regimes. The performed simulations reveal that achievement of accurate results is conditioned by a mesh resolution in thermal boundary layers near the walls, and a way in which the governing equations are formulated, i.e., the conservative or non-conservative form. This turns out more important than a formal order of discretization method. Robustness of the proposed algorithm for the computations of turbulent flow is demonstrated based on the flow in a periodic channel at Reynolds number Re τ = 200 with density ratio equal to two. In this case the profiles of mean velocity, temperature and their fluctuations are analyzed and they agree quite well with literature data. In all presented test cases the obtained pressure fields are smooth and without any oscillations observed when the collocated meshes are employed. [ABSTRACT FROM AUTHOR]

The local radial basis function (RBF) scheme is developed to simulate 2D and 3D heat transfer and flow dynamics of generalized Newtonian fluids (GNF). The local RBF scheme is a meshless numerical method based on radial basis functions with localized technique. The procedure of localization reduces the computational cost more efficiently than the traditional global RBF method. This meshless method does not require mesh generation, numerical integration and only needs point collocation. Besides, it is very easy to interpolate physical values and its derivatives everywhere in the domain. We consider one isothermal and three non-isothermal multidimensional transient GNF fluid and heat problems in this paper. The dynamic viscosity of the GNF is specified as two different models: the power law model (temperature independent) or Cross model (temperature dependent). The viscous heating is also considered in this work. Numerical results show that the local RBF scheme is stable and accurate as far as the four tested cases are concerned. [ABSTRACT FROM AUTHOR]

A study conducted by researchers from the University of Sao Paulo in Brazil explored the use of vibroacoustography as a nondestructive and noncontact technique to estimate the porosity of rock samples. The study found a relationship between the amplitude of vibroacoustic signals and the porosity of the rocks. The researchers believe that these findings could be valuable in exploring and characterizing oil reservoir rocks. The research has been peer-reviewed and published in the Journal of the Brazilian Society of Mechanical Sciences and Engineering. [Extracted from the article]

Researchers at the City University of Hong Kong have developed a new method for simulating blood flow in elastic vessels using a physics-informed neural network. Traditional methods for simulating blood flow have limitations when it comes to real-life scenarios, but this new approach offers flexibility and efficiency in handling complex geometries. The researchers conducted experiments on regular cylinder vessels and vessels with plaque on their walls, comparing their results to a solution calculated by finite element methods. The study concluded that their method had advantages in terms of relative error and time consumption. [Extracted from the article]

Researchers from the Hebrew University of Jerusalem have developed a new method for fabricating fluidic circuits using laser printing technology. The method allows for rapid prototyping of macrofluidic devices with control over fluid manipulation and environmental conditions. The researchers tested the laser-printed macrofluidics in various settings and found that they performed well in controlling fluid flow and maintaining environmental conditions. This approach has the potential to advance research and innovation in fluidics, biomedical research, synthetic biology, tissue engineering, and STEM education. [Extracted from the article]

The motion of the small vortices in the dissipation region (large wave number) is not fully understood due to the influence of the kinematic viscosity and energy dissipation rate. Studying the motion law of small vortices is of great significance to understand the physical mechanism of turbulence. It is well known that the motion of small vortices is statistically isotropic in the dissipation region. Liutex is a new physical quantity recently found to define the rigid rotation of fluids in turbulent flow. In this study, the turbulent flow of boundary layer on a flat plate at freestream Mach number of 0.5 was studied based on a high-order direct numerical simulation (DNS). Using our DNS of flat plate and one DNS of plane turbulent channels of Fluid Dynamics Group UPM, the spectrum of Liutex is analyzed, and the similarity law of Liutex in the dissipation region is obtained. The study results show that the wavenumber spectrum of Liutex exactly follows the -5/3 law, i.e. E L (κ) ∼ C κ − 5 / 3 , where κ = 1 / l is the wavenumber and E L is the amplitude of the Liutex spectrum. The scaling of Liutex with the frequency shows a same law of -5/3, since turbulent vortices propagate downstream with almost equal speeds. This paper reports the Liutex similarity for the dissipation subrange of different areas in fully developed turbulent boundary layers at low Reynolds number. Meanwhile, the vorticity and Q-criteria are found having no such similarity in boundary layers due to the shear contamination. [ABSTRACT FROM AUTHOR]

Two different families of planar exact solutions for second grade fluid flows are derived in this paper. Exact solutions for Newtonian fluid flows are derived as particular case when normal stress moduli vanish. The novelty of the solutions is that they are obtained by assuming the stream functions as a finite sum of functions with different arguments. An important property of the derived solutions is that solutions in a given family are all superposable flows. The first family of solutions can be considered as a generalization of rectangular array of Taylor vortices as these classical solutions are special cases of the derived exact solutions. A subfamily of spatially periodic exact solutions for both Newtonian and non-Newtonian fluid flows are also derived. The complex structures of the two dimensional vortices are illustrated in several cases. • Two new families of exact solutions for second grade fluid flows are derived. • These solutions are classified as generalized Taylor vortices. • The solutions in a given family are superposable flows. • Subfamily of spatially periodic solutions are constructed. • Exact solutions for Newtonian flows are also derived. [ABSTRACT FROM AUTHOR]

• A formulation of normalized SPH method for modeling inviscid fluid flows is derived. • Rigorous methods are proposed for imposing dynamic boundary condition at free surface. • An efficient method based on kernel estimation is proposed for calculation of boundary summation. • The normalized SPH method is successfully applied to modeling large deformation of free surface. • The normalized SPH method can produce higher accuracy than the conventional SPH method. A new normalized smoothed particle hydrodynamics (SPH) method has been presented recently and applied to transient solid mechanics problems of small deformation. The method can overcome boundary deficiency of the conventional SPH method without troublesome inversion of corrective matrix and provide convenience for treating boundary conditions. In this paper, a formulation of the normalized SPH method is derived for modeling inviscid fluid flows with large deformation of free surface. The treatment of dynamic free surface boundary conditions in the present method is addressed and theoretically compared with that in the conventional SPH method. A method based on kernel estimation is proposed for calculation of boundary summation and compared with the method based on α -shape. The normalized SPH method is applied to modeling inviscid free surface flows. Numerical results demonstrate that the present method is capable of modeling large deformation of free surface and can produce higher accuracy than the conventional SPH method, especially at boundary regions. The newly developed kernel estimation method for the calculation of boundary summation is more efficient than the α -shape-based method, and makes the computational efficiency of the normalized SPH method close to the conventional SPH method. To simulate violent free surface flows, a particle shifting technique is introduced in the present method. With this technique, the method is applied to simulating extremely large deformation, fragmentation and reconnection of free surface. [ABSTRACT FROM AUTHOR]

In this paper, an HLLC-type contact preserving Riemann solver for incompressible two-phase flows using the artificial compressibility formulation is presented. This formulation is an improvement over the previous HLLC-VOF formulation (Bhat and Mandal, 2019). In this work, unlike the previous formulation, the variation of the volume fraction is taken into account when calculating the eigenvalues and eigenvectors. Hence, the equations for the intermediate states and the intermediate wave speed are closely-coupled with density variation during pseudo-time evolution of the solution. Additionally, an interface compression algorithm is used in tandem to ensure sharp interfaces. This modified Riemann solver (called HLLC-VOF-M) is found to be more robust and accurate compared to the older HLLC-VOF solver and the non-contact preserving HLL solver. Several test problems in two- and three-dimensions are solved to demonstrate and evaluate the efficacy of the solver on structured and unstructured meshes. • Contact wave preserving Riemann solver for three-dimensional, incompressible two-phase fluid flows. • Artificial compressibility formulation closely-coupled with the volume of fluid method. • Sharp fluid interfaces are maintained using interface compression coupled with Riemann solver. • Viscous flux is computed using least-squares and surface tension is incorporated using the CSS model. • Robust formulation which is less sensitive to artificial compressibility parameter, based on several 2D and 3D test problems. [ABSTRACT FROM AUTHOR]

Purpose: The material point method (MPM)is a particle-based numerical method suitable for solid–liquid simulation and large deformation problems. However, MPM is generally used in solid deformation at present, to develop a multi-physics coupling MPM; the purpose of this study is to extend the MPM to simulate the heat and fluid flow and address the thermal-hydrological (TH) coupling problems. Design/methodology/approach: The porous medium was discretized into two sets of Lagrangian points, and the motion of fluid points follows the Darcy's law. Two sets of heat transport equations were established for the heat conduction and heat exchange in the pore fluid and solid skeleton. Fractures were considered by adding the porosity gradient term in the governing equations; also a transition function was introduced to smoothen the fracture boundary. Findings: Four cases of heat and fluid flow in porous medium and fractures were presented to verify the feasibility of the proposed method. And the effects of fractures on heat and fluid flow were investigated. Additionally, a case of geothermal extraction was solved and the importance of the interstitial convective heat transfer coefficient was analyzed. Originality/value: The proposed method extends the conventional MPM, using two sets of material points and two sets of heat transport equations to simulate the heat and fluid flow and address the TH coupling problems, which can be applied in both porous medium and fractures. [ABSTRACT FROM AUTHOR]

The paper reports a study about the prediction of flows around simplified vehicles using Partially-Averaged Navier–Stokes (PANS). Numerical simulations are performed for two simplified vehicles: a slanted-back Ahmed body at Re = 30,000 and a squared-back Ahmed body at Re = 300,000. A comparison of the resolved and modeled physical flow scales is made with corresponding LES and experimental data for a better understanding of the performance of the PANS model. The PANS model is compared for coarse and fine grid resolutions and it is indicated that even a coarse-grid PANS simulation is able to produce fairly close flow predictions to those from a well-resolved LES simulation. The results indicate the possibility of improvement of the predictions by employing a finer grid resolution. [ABSTRACT FROM AUTHOR]