Kind Of Flow Research Articles

Choice of measure source terms in interface coupling for a model problem in gas dynamics

This paper is devoted to the mathematical and numerical analysis of a coupling procedure for one-dimensional Euler systems. The two systems have different closure laws and are coupled through a thin fixed interface. Following the work of [5], we propose to couple these systems by a bounded vector-valued Dirac measure, concentrated at the coupling interface, which in the applications may have a physical meaning. We show that the proposed framework allows to control the coupling conditions and we propose an approximate Riemann solver based on a relaxation approach preserving equilibrium solutions of the coupled problem. Numerical experiments in constrained optimization problems are then presented to assess the performances of the present method. 1. Introduction The study of large-scale and complex problems exhibiting a wide range of physical space and time scales (see for instance [62, 35, 14]), usually requires separate solvers adapted to the resolution of specific scales. This is the case of many industrial flows. Let us quote, for example, the numerical simulation of two-phase flows applied to the burning liquid oxygen-hydrogen gas in rocket engines [58]. This kind of flow contains both separated and dispersed two-phase flows, due to atomization and evaporation phenomena. This requires appropriate models and solvers for separated and dispersed phases that have to be appropriately coupled. Another example concerns turbomachine flows which can be modeled by the Euler equations of gas dynamics with different closure laws between the stages of the turbine, where the conditions of temperature and pressure are strongly heterogeneous. The coupling of these different systems is thus necessary to give a complete description of the flow inside the whole turbine. The method of interface coupling allows to represent the evolution of such flows, where different models are separated by fixed interfaces. First, coupling conditions are specified at the interface to exchange information between the systems. The definition of transmission conditions generally results from physical consideration, e.g. the conservation or the continuity of given variables. Then, the transmission conditions are represented at the discrete level. The study of interface coupling for nonlinear hyperbolic systems has received attention for several years. In [43], the authors study the scalar case from both mathematical and numerical points of view.

Numerical Study of 2D and 3D Separation Phenomena in the Dam-Break Flow Interacting with a Triangular Obstacle

Dam-break turbulent flow interacting with obstacles is simulated with the VOF method implemented in an in-house unstructured-grid finite-volume Navier-Stokes code. A special attention is paid to prediction of separation phenomena using low-Re computational grids that provide full resolution of viscous sublayers on the bottom and side confining walls, if any. Some original developments aimed at improvement of the VOF method robustness for such kind of flows are presented. The test case considered is interaction of the dam-break induced water stream with a triangular obstacle. Computations under conditions of experiments by Soares-Frazao (2007) have been carried out on the base of 2D and 3D formulations. It is shown that action of the bottom wall friction leads to formation of one or two separation “bubbles”, depending on the flow development phase, and to occurrence of associated hills at the free surface, which are observed in experimental photos as well. Taking into account presence of side walls of the experimental channel results in solutions with a considerably 3D shape of the computed free surface, and its side view much better agrees with the experimental photos than that given by 2D solutions. Moreover, local-in-time separation of the flow from the side walls is predicted with the 3D formulation.

About One Discrete Mathematical Model of Perfect Fluid

In work, it is constructed a discrete mathematical model of motion of a perfect fluid. The fluid is represented as an ensemble of identical so-called liquid particles, which are in the form of extended geometrical objects: circles and spheres for two-dimensional and three-dimensional cases, respectively. The mechanism of interaction between the liquid particles on a binary level and on the level of the n-cluster is formulated. This mechanism has previously been found by the author as part of the mathematical modeling of turbulent fluid motion. In the turbulence model was derived and investigated the potential interaction of pairs of liquid particles, which contained a singularity of the branch point. Exactly, this is possible to build in this article discrete stochastic-deterministic model of an ideal fluid. The results of computational experiment to simulate various kinds of flows in two-dimensional and three-dimensional ensembles of liquid particles are presented. Modeling was carried out in the areas of quadratic or cubic form. On boundary of a region satisfies the condition of elastic reflection liquid particles. The flows with spontaneous separation of particles in a region, various kinds of eddy streams, with the quite unexpected statistical properties of an ensemble of particles characteristic for the Fermi-Pasta-Ulam effect were found. We build and study the flow in which the velocity of the particles is calibrated. It was possible using the appropriate flows of liquid particles of the ensemble to demonstrate the possibility to reproduce any prescribed image by manipulating the parameters of the interaction. Calculations of the flows were performed with using MATLAB software package according to the algorithms presented in this article.

Editors' Introduction: On the Space and Time of Urban Asia

If, as Saskia Sassen (2001; 2012) argues, the city has become ever more important in today’s globalizing world as a center mediating financial and labor flows, it is also true that these various kinds of flows have made cities increasingly complex and more difficult to define. Even as urban development projects continuously reshape the boundaries of a city, migrant cultures and populations radically change a city’s outlook and identity through their negotiations with existing infrastructure and communities. Although this is happening all over the world and is certainly not unique to Asia, we posit that it is still worth focusing on the particularities of the Asian experience of urbanization. By using the word “unique,” we do not intend to imply that cities in Asia are exceptional and thus beyond comparison with other Western or non-Western cities and urban experiences. Given Verge’s mission of emphasizing and identifying the convergences and divergences that coexist under the conceptual rubric of “Global Asias,” we contend that understanding the complexity of Asian urbanisms depends on balancing between identifying divergence via comparative frameworks and identifying convergences predicated on a methodological commitment to geographical and historical contextualization and specificity. As such, the focus of this special issue on “Asian Urbanisms and Urbanization” represents our belief that there is something both universal and specific about Asian cities. By attending to the specific histories and experiences of Asian cities, this issue encourages us simultaneously to consider “Asia” in pluralistic terms and to engage and discuss issues of global concern and impact. As the work collectively included in this issue reveals, attempts to discuss Asian experiences and processes of urbanization would do well to

Numerical simulation for flow‐induced stress in injection/compression molding

Flow‐induced stress in compression stage is complex because compression flow combines both shear flow and extensional flow characters and involves the boundary change in melt front and compressing directions. To describe this kind of flow effectively, the theoretical model was established in terms of three‐dimensional compressible and viscoelastic fluid, and the material derivative which includes mesh moving velocity was introduced to modify the convective terms in governing and constitutive equations based on Arbitrary Lagrangian Eulerian description. The corresponding variational equations were derived via Gauss formula and the finite element method was used to discretize the flow variables with mixed elements. In order to decouple the interdependence of velocity, stress, and temperature, a new approach involves twofold iterations was proposed to solve nonlinear flow problem. A new mesh updating scheme was presented to keep consistent with compressed regions. Numerical results indicate the compression can reduce the flow‐induced stress significantly compared to conventional injection molding, increase compressing velocity enlarges flow‐induced stress, and high temperature decreases flow‐induced stress. The proposed method was verified by photoelastic pictures and measured pressures and temperatures during molding. POLYM. ENG. SCI., 56:287–298, 2016. © 2015 Society of Plastics Engineers

The maximum sustainable heat flux in stably stratified channel flows

In analogy to the nocturnal atmospheric boundary layer, a flux‐driven, cooled channel flow is studied using direct numerical simulations. In agreement with earlier studies, turbulence collapses when the surface cooling exceeds a critical value. In that case, laminarization occurs. Here, the so‐called maximum sustainable heat flux (MSHF) hypothesis is tested. It explains why laminarization will occur at strong cooling rates. It states that in stratified flows the downward heat flux is limited to a maximum, which, in turn, is determined by the momentum of the flow. If the heat extraction at the surface exceeds this maximum, near‐surface stability will increase rapidly, which hampers efficient vertical heat transport further. This positive feedback eventually causes turbulence to be suppressed fully by the intensive density stratification. This framework is used to predict the collapse of turbulence and a good agreement between theory and simulations is found. Therefore, it is concluded that the maximum sustainable heat flux mechanism explains the collapse of turbulence in this kind of flow. In future work, there is the need for an extension to more realistic configurations, allowing for Coriolis effects and more realistic surface boundary conditions.

The Concept of the Regional Industrial Cluster Information Support

One of the priorities and internationally accepted approaches to the management of innovation processes in the global economy is the cluster approach, a product of the integration of economic processes, which is a powerful tool to promote regional development. It has been effectively studied in the article the regional cluster with data items to ensure the effective interaction of all participants in the process of achieving economic goals. The paper presents an algorithm of information modeling of regional industrial cluster, comprising the steps of determining the hierarchical structure of the processes, the organization of all kinds of flows, the description of the logical structure and the information needs of each process. This article is intended for economists, researchers, enterprises executives, professionals in the field of information technology, dealing with information support of manufacturing processes. DOI: 10.5901/mjss.2015.v6n2s3p29

Modeling and simulation of mixing in water-in-oil emulsion flow through a valve-like element using a population balance model

Emulsion flows are very common in natural processes as well as in several engineering areas, such as in the process of desalting crude oil that occurs in refineries. This kind of flow is described as a polydispersed multiphase flow. In this work, we evaluated the behavior of water-in-oil emulsion flowing through a duct with an element used to mimic the effect of a globe valve. An Eulerian multi-fluid approach was employed by solving the population balance equation coupled with computational fluid dynamics. Coalescence and breakage models recently developed were extended to this inhomogeneous model. A bivariate population balance problem was also solved to demonstrate the mixing caused by the valve-like element. The simulated results showed good agreement with the available experimental data for the Sauter and DeBroukere mean diameters.

Numerical simulation for two-phase flow in a porous medium

In this paper, we introduce a numerical study of the hydrocarbon system used for petroleum reservoir simulations. This system is a simplified model which describes a two-phase flow (oil and gas) with mass transfer in a porous medium, which leads to fluid compressibility. This kind of flow is modeled by a system of parabolic degenerated non-linear convection-diffusion equations. Under certain hypotheses, such as the validity of Darcy’s law, incompressibility of the porous medium, compressibility of the fluids, mass transfer between the oil and the gas, and negligible gravity, the global pressure formulation of Chavent (Mathematical Models and Finite Elements for Reservoir Simulation: Single Phase, Multiphase and Multicomponent Flows Through Porous Media, 1986) is formulated. This formulation allows the establishment of theoretical results on the existence and uniqueness of the solution (Gasmi and Nouri in Appl. Math. Sci. 7(42):2055-2064, 2013). Furthermore, different numerical schemes have been considered by many authors, among others we can refer the reader to (Chen in Finite element methods for the black oil model in petroleum reservoirs, 1994; Chen in Reservoir Simulation: Mathematical Techniques in Oil Recovery, 2007) and (Gagneux et al. in Rev. Mat. Univ. Complut. Madr. 2(1):119-148, 1989). Here we make use of a scheme based on the finite volume method and present numerical results for this simplified system.

Constructal vascularized structures

AbstractSmart features such as self-healing and selfcooling require bathing the entire volume with a coolant or/and healing agent. Bathing the entire volume is an example of point to area (or volume) flows. Point to area flows cover all the distributing and collecting kinds of flows, i.e. inhaling and exhaling, mining, river deltas, energy distribution, distribution of products on the landscape and so on. The flow resistances of a point to area flow can be decreased by changing the design with the guidance of the constructal law, which is the law of the design evolution in time. In this paper, how the flow resistances (heat, fluid and stress) can be decreased by using the constructal law is shown with examples. First, the validity of two assumptions is surveyed: using temperature independent Hess-Murray rule and using constant diameter ducts where the duct discharges fluid along its edge. Then, point to area types of flows are explained by illustrating the results of two examples: fluid networks and heating an area. Last, how the structures should be vascularized for cooling and mechanical strength is documented. This paper shows that flow resistances can be decreased by morphing the shape freely without any restrictions or generic algorithms.

S0510303 Couette流れと干渉する衝突噴流の熱伝達に関する研究

Impinging jet is widely used in industrial fields, such as thermal management of electronic devices or jet washing. In addition, we can see many both of numerical and experimental studies on interfering flows between mainstream or Hagen-Poiseuille and impinging jet. These kinds of flows are well appearing at T-shape merging pipe flows or film cooling on turbine blades. However, there are few studies on heat transfer field interfering Couette flow and impinging jet, in spite of typical flow such as cooling rotary inner-cylinder of bearing, cooling rolled steel in its production process and carrier gas flow of Additive Manufacturing (A.M.). Especially for industrial using of A.M., it becomes a huge obstacle due to its much complicated multi-physical mechanism between the moving grinding table and the jet including carrier gas and additive particle. Therefore, we have studied numerically on the heat transfer of impinging jet interfering with Couette flow, and compared with several different jet inlet angles. In this study, we used DNS which employing secondary conservative second order central difference scheme for convective terms of Navier-Stokes equations and heat transport equation to obtain unsteady flow and temperature scalar fields. Then, we confirmed this DNS results agree qualitatively with those of Quasi-DNS which had been done in our former studies.

From dys/function to flow: Inception, perception and dancing beyond life's constraints.

When the existential state of flow is experienced, the flesh of oneself perceptually intertwines with the Merleau-Pontian flesh of the world. Perceived constraints and worries disappear and, according to Csikszentmihalyi (1996, 2000, 2008), longtime researcher of flow, all that exists is the merging of bodily action and awareness within the timeless nature of the present moment. Such a state is highly desirable and for those who experience flow often; the path toward its onset might become automatic, even predictable. But what might it be like to experience a dys/function, such as an injury that veers one from this automatic-pilot course? Could such a circumstance, if mindfully embraced with a Heideggerian sway, cultivate a different kind of flow? Influenced by Daniel Stern's (2010) concept of vitality forms, an affective attunement towards movement that attends to the nuances of force, spatiality, and intentionality/directionality within motility, this inquiry delves into the motile experience of finding...

Does Foreign Capital Enhance Economic Growth In Emerging Countries: Flow Decomposition Approach?

Unlike trade liberalization, the impact of financial openness on growth is still mitigated. In fact, empirical studies focusing on effects of capital account liberalization are inconclusive, which could be due to the sample chosen, to the liberalization index or to the fact that studies take account of capital inflows as a whole which can mask substantial differences between different flow effects.Our purpose in this paper is on one hand to re-examine the impact of capital inflows on growth by dividing these inflows into portfolio equity flows, foreign direct investment flows and debt flows and on the other hand to study if the composition of capital inflows has an importance. This work will be done by estimating a standard growth model using dynamic panel data approach.Our main findings are first, that total capital inflows improve economic growth and so does every kind of flow taken apart; which supports the neoclassical wisdom and second, that capital inflows composition isn't important; which indicates that all inflows are substitutes in the short term.

Boundary elements method for microfluidic two-phase flows in shallow channels

In the following work we apply the boundary element method to two-phase flows in shallow microchannels, where one phase is dispersed and does not wet the channel walls. These kinds of flows are often encountered in microfluidic Lab-On-A-Chip devices and characterized by low Reynolds and low capillary numbers.Assuming that these channels are homogeneous in height and have a large aspect ratio, we use depth-averaged equations to describe these two-phase flows using the Brinkman equation, which constitutes a refinement of Darcy’s law. These partial differential equations are discretized and solved numerically using the boundary element method, where a stabilization scheme is applied to the surface tension terms, allowing for a less restrictive time step at low capillary numbers. The convergence of the numerical algorithm is checked against a static analytical solution and on a dynamic test case. Finally the algorithm is applied to the non-linear development of the Saffman–Taylor instability and compared to experimental studies of droplet deformation in expanding flows.

Transition to ballistic regime for heat transport in helium II

The size-dependent and flux-dependent effective thermal conductivity of narrow capillaries filled with superfluid helium is analyzed from a thermodynamic continuum perspective. The classical Landau evaluation of the effective thermal conductivity of quiescent superfluid, or the Gorter-Mellinck regime of turbulent superfluids, are extended to describe the transition to ballistic regime in narrow channels wherein the radius $R$ is comparable to (or smaller than) the phonon mean-free path $\ell$ in superfluid helium. To do so we start from an extended equation for the heat flux incorporating non-local terms, and take into consideration a heat slip flow along the walls of the tube. This leads from an effective thermal conductivity proportional to $R^2$ (Landau regime) to another one proportional to $R\ell$ (ballistic regime). We consider two kinds of flows: along cylindrical pipes and along two infinite parallel plates.

Investigation of DC flow effects on a 4K two-stage pulse tube cryocooler

Sumitomo Heavy Industries, Ltd. (SHI) has been continuously developing 4K GM-type pulse tube cryocoolers for cooling superconducting magnets and pre-cooling ultra-low temperature refrigerators, such as dilution refrigerators, etc. In a double-inlet or a 4-valve GM-type pulse tube cryocooler, there is a gas circulation, called DC flow, generated by the pulse tube, the regenerator and the orifice. The performance of a pulse tube cryocooler is strongly dependent on the rate of such kind of flow. It is possible to improve the performance by optimizing the rate. In order to optimize the rate, a bypass line with a small valve is installed between the warm end of the pulse tube and the low pressure side of the compressor. The second stage cooling capacity at 4.2 K was improved by about 0.25 W after optimization of the rate by adjusting the opening of the valve. The details of the experiment results will be reported in this paper.

Simulation of two-phase fluid mixture flow in rectangular two-inlet cavity using lattice Boltzmann method

In this paper, two-phase fluid mixture flow in rectangular two-inlet cavity is studied using lattice Boltzmann method (LBM). To simulate two-phase fluids with large viscosity difference, the pseudo-potential model is improved. The improved model is verified for surface tension through Laplace's law and shown much better performance in simulating fluids with large viscosity difference than pseudo-potential model. The multiple-relaxation-time (MRT) scheme is used to enhance numerical stability. Then the two-phase fluid mixture flow with same and different viscosity in two-inlet cavity is simulated by present lattice Boltzmann (LB) model, pseudo-potential LB model and volume-of-fluid (VOF) method, respectively. The comparison of these numerical results shows that LB model is more suitable for such kind of flow than VOF method, since it can reflect repulsive forces and transitional region of two-phase fluids in dynamic process. Moreover, it also shows that present LB model has better dynamic stability than pseudo-potential model. Furthermore, simulations of the two-phase fluid mixture flow with different fluid viscosities, inlet velocities, inlet heights and outlet positions using present LB model are presented, exhibiting their effect to contact area of fluids.

Simultaneous measurement of temperature and velocity fields in convective air flows

Thermal convective air flows are of great relevance in fundamental studies and technical applications such as heat exchangers or indoor ventilation. Since these kinds of flow are driven by temperature gradients, simultaneous measurements of instantaneous velocity and temperature fields are highly desirable. A possible solution is the combination of particle image velocimetry (PIV) and particle image thermography (PIT) using thermochromic liquid crystals (TLCs) as tracer particles. While combined PIV and PIT is already state of the art for measurements in liquids, this is not yet the case for gas flows. In this study we address the adaptation of the measuring technique to gaseous fluids with respect to the generation of the tracer particles, the particle illumination and the image filtering process. Results of the simultaneous PIV/PIT stemming from application to a fluid system with continuous air exchange are presented. The measurements were conducted in a cuboidal convection sample with air in- and outlet at a Rayleigh number Ra ≈ 9.0 × 107. They prove the feasibility of the method by providing absolute and relative temperature accuracies of σT = 0.19 K and σΔT = 0.06 K, respectively. Further open issues that have to be addressed in order to mature the technique are identified.

S0520204 シックナー内部の流れ解析とそのスラリーモデルの検討([S052-02]複雑流体の流動現象(2))

Non-Newton fluid is utilized for many kinds of industrial products. Moreover, a slurry flow in HPAL method is typical Non-Newton flow and has shear stress overshoot in the low shear rate region. It is well known that the Bingham and Casson models are treated as the Non-Newton fluid. However, these models do not have the shear stress overshoot. In this study, the authors carry out the flow simulation in the Thickner of the HPAL method by three kinds of Non-Newton fluid models using ANSYS14.0/ANSYS CFX14.0. As a result, we visualized the interaction of two kinds of flow, such as around the lake and near the inlet, by the new Non-Newton model considered with shear stress overshoot.

Compact representation of wall-bounded turbulence using compressive sampling

Compressive sampling is well-known to be a useful tool used to resolve the energetic content of signals that admit a sparse representation. The broadband temporal spectrum acquired from point measurements in wall-bounded turbulence has precluded the prior use of compressive sampling in this kind of flow, however it is shown here that the frequency content of flow fields that have been Fourier transformed in the homogeneous spatial (wall-parallel) directions is approximately sparse, giving rise to a compact representation of the velocity field. As such, compressive sampling is an ideal tool for reducing the amount of information required to approximate the velocity field. Further, success of the compressive sampling approach provides strong evidence that this representation is both physically meaningful and indicative of special properties of wall turbulence. Another advantage of compressive sampling over periodic sampling becomes evident at high Reynolds numbers, since the number of samples required to resolve a given bandwidth with compressive sampling scales as the logarithm of the dynamically significant bandwidth instead of linearly for periodic sampling. The combination of the Fourier decomposition in the wall-parallel directions, the approximate sparsity in frequency, and empirical bounds on the convection velocity leads to a compact representation of an otherwise broadband distribution of energy in the space defined by streamwise and spanwise wavenumber, frequency, and wall-normal location. The data storage requirements for reconstruction of the full field using compressive sampling are shown to be significantly less than for periodic sampling, in which the Nyquist criterion limits the maximum frequency that can be resolved. Conversely, compressive sampling maximizes the frequency range that can be recovered if the number of samples is limited, resolving frequencies up to several times higher than the mean sampling rate. It is proposed that the approximate sparsity in frequency and the corresponding structure in the spatial domain can be exploited to design simulation schemes for canonical wall turbulence with significantly reduced computational expense compared with current techniques.