Single-Fluid Approach: Example of Dam's ?-∊ Model

An improved progressive preconditioning method for analyzing steady inviscid and laminar flows around fully wetted and sheet‐cavitating hydrofoils is presented. The preconditioning matrix is adapted automatically from the pressure and/or velocity flow‐field by a power‐law relation. The cavitating calculations are based on a single fluid approach. In this approach, the liquid/vapour mixture is treated as a homogeneous fluid whose density is controlled by a barotropic state law. This physical model is integrated with a numerical resolution derived from the cell‐centered Jameson's finite volume algorithm. The stabilization is achieved via the second‐and fourth‐order artificial dissipation scheme. Explicit four‐step Runge–Kutta time integration is applied to achieve the steady‐state condition. Results presented in the paper focus on the pressure distribution on hydrofoils wall, velocity profiles, lift and drag forces, length of sheet cavitation, and effect of the power‐law preconditioning method on convergence speed. The results show satisfactory agreement with numerical and experimental works of others. The scheme has a progressive effect on the convergence speed. The results indicate that using the power‐law preconditioner improves the convergence rate, significantly. Copyright © 2010 John Wiley & Sons, Ltd.

In partially ionised plasmas, the magnetic field can become decoupled from the neutral gas and diffuse through it in a process known as ambipolar diffusion. Although ambipolar diffusion has been implemented in several grid codes, we here provide an implementation in smoothed particle magnetohydrodynamics (SPMHD). We use the strong coupling approximation in which the ion density is negligible, allowing a single fluid approach. The equations are derived to conserve energy, and to provide a positive definite contribution to the entropy. We test the implementation in both a simple 1D SPMHD code and the fully 3D code PHANTOM. The wave damping test yields agreement within 0.03-2 per cent of the analytical result, depending on the value of the collisional coupling constant. The oblique C-shocks test yields results that typically agree within 4 per cent of the semi-analytical result. Our algorithm is therefore suitable for exploring the effect ambipolar diffusion has on physical processes, such as the formation of stars from molecular clouds.

An experiment-calculated investigation of forced convection of nanofluids based on Al2O3 nanoparticles was carried out. The hydrodynamic description and a model of homogeneous nanofluids were used. The homogeneous nanofluids model assumes that the hydrodynamics and heat transfer can be described by conventional Navier-Stokes and heat transfer equations with the physical parameters corresponding to nanofluids. The results showed that this model very well described the experimental data in some cases. However, in some other cases, there are discrepancies between experiment and theory that can be explained by the real heterogeneity of nanofluids and the errors in the experimental determination of thermal conductivity and viscosity of nanofluids.

Periodically unsteady shedding of partial cavity and forming of cavitation cloud have a great influence on hydraulic performances and cavitation erosion for ship propellers and hydro machines. In the present study, the unsteady cavitating flow around a hydrofoil has been calculated by using the single fluid approach with a developed cavitation mass transfer expression based on the vaporization and condensation of the fluid. The numerical simulation depicted the unsteady shedding of partial cavity, such as the process of cavity developing, breaking off and collapsing in the downstream under the steady incoming flow condition. It is noted that good agreement between the numerical results and that of experiment conducted at a cavitation tunnel is achieved. The cavitating flow field indicates that the cavity shedding was mainly caused by the re-entrant jet near cavity trailing edge, which was also clearly recorded by high-speed photographing.

Two energetic events in the Earth’s magnetotail detected by Geotail are examined with detailed analysis of three-dimensional velocity phase space density. It is found that the occurrence of multiple ion components is high during these dynamic episodes. Different populations evolve independently of each other, suggesting particles from multiple activity sites contributing to the observed phase space density. The transport properties with consideration of multiple components are evaluated, with the result showing significant differences from those based on a single fluid approach. This comparison indicates that precise evaluation of the energy and magnetic flux transport of energetic events in the magnetotail requires resolving individual populations in the phase space density.

CFD modelling of the condensation inside a Supersonic Nozzle: implementing customized wet-steam model in commercial codes

The present paper is devoted to the computation of single phase or two phase flows using the single-fluid approach. Governing equations rely on Euler equations which may be supplemented by conservation laws for mass species. Emphasis is given on numerical modelling with help of Godunov scheme or an approximate form of Godunov scheme called VFRoe-ncv based on velocity and pressure variables. Three distinct classes of closure laws to express the internal energy in terms of pressure, density and additional variables are exhibited. It is shown first that a standard conservative formulation of above mentioned schemes enables to predict “perfectly” unsteady contact discontinuities on coarse meshes, when the equation of state (EOS) belongs to the first class. On the basis of previous work issuing from literature, an almost conservative though modified version of the scheme is proposed to deal with EOS in the second or third class. Numerical evidence shows that the accuracy of approximations of discontinuous solutions of standard Riemann problems is strengthened on coarse meshes, but that convergence towards the right shock solution may be lost in some cases involving complex EOS in the third class. Hence, a blend scheme is eventually proposed to benefit from both properties (“perfect” representation of contact discontinuities on coarse meshes, and correct convergence on finer meshes). Computational results based on an approximate Godunov scheme are provided and discussed.

Multidimensional metabolic analysis has become a new trend in establishing efficient disease monitoring systems, as the constraints associated with relying solely on a single dimension in refined monitoring are increasingly pronounced. Here, coordination polymers are employed as derivative precursors to create multishell hollow hybrids, developing an integrated metabolic monitoring system. Briefly, metabolic fingerprints are extracted from hundreds of serum samples and urine samples, encompassing not only membranous nephropathy but also related diseases, using high-throughput mass spectrometry. With optimized algorithm and initial feature selection, the established combined panel demonstrates enhanced accuracy in both subtype differentiation (over 98.1%) and prognostic monitoring (over 95.6%), even during double blind test. This surpasses the serum biomarker panel (≈90.7% for subtyping, ≈89.7% for prognosis) and urine biomarker panel (≈94.4% for subtyping, ≈76.5% for prognosis). Moreover, after attempting to further refine the marker panel, the blind test maintains equal sensitivity, specificity, and accuracy, showcasing a comprehensive improvement over the single-fluid approach. This underscores the remarkable effectiveness and superiority of the integrated strategy in discriminating between MN and other groups. This work has the potential to significantly advance diagnostic medicine, leading to the establishment of more effective strategies for patient management.

Proto-neutron stars with dark matter admixture: A single-fluid approach

The phenomenon of boiling is visible all around us from cooking to power generation, but despite such all around usages many aspects of boiling are still not very well understood as it is a very complex process and occurs over a wide range of system scales. We often rely on empirical correlations when we want to evaluate different parameters connected with boiling phenomena. Along with the development of empirical correlations for engineering applications, considerable advances are there in understanding the fundamentals of the boiling process. Since the process is very complex and multiple thermal and fluid variables are involved, a complete theoretical model for predicting the boiling heat transfer is yet to be developed. Boiling phenomenon is still being intensively studied and is the focus of research activities in numerous institutions across the world. A better understanding of the physics of boiling can be achieved by either detailed measurements or high-resolution numerical simulation. These two approaches are now complementing each other in understanding the physics of boiling more completely. In recent years, numerical modeling has improved considerably thanks to ever-increasing computational power. With advancing computing capabilities and advent of new numerical techniques for two-phase flow, simulations of boiling heat transfer have become feasible. The main two approaches in numerical simulation of boiling are (i) interpenetrating media approach and (ii) single-fluid approach. In addition to this, some newer techniques like the phase field method and the lattice Boltzmann method have to some extent been used for simulating boiling flows. In this review, we look at the different approaches of numerical simulation of boiling currently being used.

Direct numerical simulation of mass transfer and mixing in complex two-phase systems using a coupled volume of fluid and immersed boundary method

Condensation processes in a motoring engine

Onshore wind can significantly affect wave overtopping process and increase mean overtopping discharge. Thus, the wind should be an important variable in coastal design process. However, despite many researches have analyzed the influence of wind on the overtopping, there is still a lack of exhaustive knowledge about this phenomenon. To further analyze the wind effects, the CFD model FLOW-3D has been used to investigate wave overtopping at vertical seawalls. The single-fluid approach has been adopted, i.e. the presence of wind has been simulated via the wind shear stress on the sea surface. The main aim of this work is to verify the ability of this simplified numerical modelling to capture the macro-processes involved in the phenomenon of wave overtopping. The presence of wind shear stress has led to physically consistent results. It confirmed that as the mean overtopping discharge decreases, as the wind effect increases. Furthermore, numerical results have shown that the advection of water droplets behind the structure by the wind is the key mechanism for the enhancement of wave overtopping. Finally, by gathering numerical results and laboratory data carried out by Durbridge (2021), a new predictive formula to estimate the wind factor is provided.

A new lattice Boltzmann model for binary mixtures, which can naturally include both the two-fluid approach and the single-fluid approach, is developed. The model is derived from the continuous kinetic model proposed by Hamel, which independently takes into account self-collisions and cross collisions. The original kinetic model is discussed in order to appreciate that cross collisions realize an internal coupling force, proportional to the diffusion velocity, and an additional coupling effect in the effective stress tensor, proportional to the deformation of the barycentric velocity field. For this reason, Hamel’s model is the natural forerunner of all linearized models based on the two-fluid approach and allows us to describe binary mixtures at different limiting regimes consistently. A discrete lattice Boltzmann model, which recovers the original Hamel’s model with second-order accuracy in both time and space, is proposed. This discrete model can analyze ordinary diffusion, pressure diffusion, and forced diffusion.

In high-pressure fuel injection systems, cavitation is known to affect spray atomization processes. Modeling the cavitation phenomenon has become a necessity to ensure predictive quality and higher fidelity of the fuel spray simulations. Inside the fuel injectors, local pressures drop below the saturation pressure of fuels in regions of flow separations, such as inlet of holes and periphery of needles at low-lift conditions. Several cavitation models and multiphase modeling approaches have been employed in the literature to predict the extent of cavitation in the fuel injection systems. A review of these modeling approaches will be presented. Amongst the cavitation models, bubble-based and semi-empirical timescale-based ones are widely used. Mixture/single-fluid and Eulerian–Eulerian/two-fluid approaches have been adopted for fuel injection cavitation modeling. Two-fluid approach captures the interaction between the two phases, which is usually ignored in single-fluid approach. Comparative studies in the literature will be reviewed here to provide a comprehensive idea of the cavitation modeling approaches to the readers. The advantages and disadvantages of these models will be discussed in depth. Keeping in mind the conflicting requirements of accuracy and constraints of computational cost, recommendations will be provided for suitable cavitation modeling approaches.