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The purpose of this study is to investigate the monodisperse cavitation of bubbly mixture flow for water and hydrogen mixture flows through a nozzle having a stenosis on the wall.

Two flow regions, namely, quasi-statically stable and quasi-statically unstable increase in the bubble radius, are considered. Different oscillating periods of bubbles in downstream corresponding to various values of Reynolds number are taken into account. The Range–Kutta method is used to tackle nonlinear coupled system of governing equations.

It is observed that for the larger values of Reynolds number, the void fraction at the upstream section, even at small values, yields instabilities at the downstream. Consequently, owing to sudden increase in the velocity, the bubbles strike the wall with high speed that eventually remove the existing stenosis. This process can be considered as an effective cardiac surgery for arteries with semi-blockage.

Original research work and to the best of author’s knowledge, this model is reported for the first time.

While many stepped spillways geometry design guidelines were developed for flat steps, designing pooled steps might be an appropriate alternative to spillways working more efficiency. This paper aims to deal with the inception point of air-entrainment and void fraction in the different height of the pools. Following that, pressure distribution was evaluated in aerated and non-aerated regions under the effect of different heights of the pools and slopes through the use of the FLOW-3D software. Comparison of obtained numerical results with experimental ones was in good agreement for all discharges used in this study. Pools height had the insignificant effect on the inception point location. The value of void fraction was more affected in lower discharges in comparison with higher ones. Negative pressure was not seen over the crest of spillway (non-aerated region), and the maximum pressure values were obtained for pools with 15 cm height along the crest in each discharge. In all slopes, negative pressure was not formed near the step bed in the pooled and flat stepped spillways. However, negative pressure was formed in more area near the vertical face in the flat stepped spillway compared with the pooled stepped spillway which increases the probability of cavitation phenomenon in the flat stepped chute.

A pooled stepped spillway was used in order to evaluate pressure, void fraction, and inception point. Also, different height of the pools was used. Numerical simulation of this study was fulfilled through Flow-3D software. The obtained results indicated that pools can affect two-phase flow characteristics including pressure, void fraction and inception point.

Over the crest, negative pressure was not seen. Pressure values were different for all used heights and the maximum ones obtained for 15 cm height. Also, pooled stepped played a more effective role in reducing the negative pressure points compared with flat cases. Inception point location was more affected in nappe and transition flow regimes in comparison with skimming flow regime particularly for 9 and 15 cm heights.

The research results of Felder et al. (2012a) from the University of Queensland were used to numerically simulate the flow over the pooled stepped spillway.

A simulation framework that includes a finite element analysis (FEA) and computational fluid dynamics (CFD) model is generated to study the effect of unstable two-phase flow-induced vibrations at a vertical 90° pipe bend. The corresponding fluid-structure interaction (FSI) of an unstable flow may pose danger to the piping structure. This paper intends to discuss this interaction.

Four cases of flows under the slug flow and churn flow regimes were investigated. The flow regimes vary in superficial gas velocities with velocities from 0.978 m/s to 9.04 m/s, while the superficial liquid velocity is kept constant at 0.61 m/s. The pipe model consists of an internal diameter of 0.0525 m, a bend radius of 0.0762 m, and a stainless-steel pipe structure.

Results show that the average unstable void fractions increase with the superficial gas velocities, but the peak frequencies were constant at 13 Hz for three of the cases. The total displacement and von Mises stress increase with a declining rate in each subsequent case, while the RMS of von Mises stress begins to stall at superficial gas velocities between 5 m/s and 9.04 m/s. The peak frequencies of von Mises stress decrease in each subsequent case.

The proposed model can be used to investigate the FSI effect of unstable void fractions at pipe bends and could assist in the development of piping systems in which the use of piping elements arranged close together are unavoidable.

The purpose of this paper is to quantify the relative importance of the multiphase model for the simulation of a gas bubble impacted by a normal shock wave in water. Both the free-field case and the collapse near a wall are investigated. Simulations are performed on both two- and three-dimensional configurations. The main phenomena involved in the bubble collapse are illustrated. A focus on the maximum pressure reached during the collapse is proposed.

Simulations are performed using an inviscid compressible homogeneous solver based on different systems of equations. It consists in solving different mixture or phasic conservation laws and a transport-equation for the gas volume fraction. Three-dimensional configurations are considered for which an efficient massively parallel strategy was developed. The code is based on a finite volume discretization for which numerical fluxes are computed with a Harten, Lax, Van Leer, Contact (HLLC) scheme.

The comparison of three multiphase models is proposed. It is shown that a simple four-equation model is well-suited to simulate such strong shock-bubble interaction. The three-dimensional collapse near a wall is investigated. It is shown that the intensity of pressure peaks on the wall is drastically increased (more than 200 per cent) in comparison with the cylindrical case.

The study of bubble collapse is a key point to understand the physical mechanism involved in cavitation erosion. The bubble collapse close to the wall has been addressed as the fundamental mechanism producing damage. Its general behavior is characterized by the formation of a water jet that penetrates through the bubble and the generation of a blast wave during the induced collapse. Both the jet and the blast wave are possible damaging mechanisms. However, the high-speed dynamics, the small spatio-temporal scales and the complicated physics involved in these processes make any theoretical and experimental approach a challenge.

Cavitation erosion is a major problem for hydraulic and marine applications. It is a limiting point for the conception and design of such components.

Such a comparison of multiphase models in the case of a strong shock-induced bubble collapse is clearly original. Usually models are tested separately leading to a large dispersion of results. Moreover, simulations of a three-dimensional bubble collapse are scarce in the literature using such fine grids.

Low combustion completeness has been the main defect of hybrid rockets. The present study tries to address the problem by bringing up the setup of the precombustion zone, which do not increase the manufacture cost and complexity.

A precombustion zone can provide a space for the liquid oxidizer to vaporize before entering the combustion zone, and prevents the endothermic effect of liquid oxidizer which can block the chemical reaction as well as the fuel regression. Therefore, this design is expected to raise the combustion completeness. The numerical simulation focuses on the flow field inside a cylindrical hybrid combustor. The distribution of temperature, combustion mode, mass fraction of reactants, velocity, combustion completeness, and solid‐fuel regression rate are presented.

With the setup of prevaporized zone of appropriate length, the upstream separation bubble which is unobvious for the case with no prevaporized zone can increase the mixing of reactants, and then increases the combustion completeness. Besides, the radial temperature distribution is more uniform. But when the length of prevaporized zone exceeds about one fourth of the combustor length, due to no enough space for the reactants to react, the combustion completeness begins to decrease and the radial temperature distribution becomes uneven. Therefore, a prevaporized zone with about 24 per cent of the combustor length can have optimum combustion completeness in the present study.

This study provides a useful design to raise the combustion completeness of a traditional hybrid rocket. However, the manufacture cost and complexity are not increased. So the results can be a good reference for the hybrid rocket designers.

The volume of fluid (VOF) method is a numerical technique to track the developing free surfaces of liquids in motion. This method can, for example, be applied to compute the liquid flow patterns in a rotating cone reactor. For this application a spherical coordinate system is most suited. The novel derivation of the extended VOF algorithms for this class of applications is presented here. Some practical limitations of this method, that are inherent in the geometry of the described system, are discussed.

The transient vaporous and gaseous cavitation phenomena in an elastic pipeline are investigated for homogeneous liquid‐gas mixture flow. It has been shown, in the case of two components having the same velocity, that modelling is also possible by considering the continuous character of the medium, i.e. without any location of column separation. The governing equations have been solved by using two finite difference schemes: the Mac Cormack’s scheme and an improved new finite difference two‐time step scheme. Characteristics method is used at the boundaries. The theoretical results obtained are compared and found to correlate well with similar results.

This paper seeks to discuss a mechanistic modeling concept for local phenomena governing two‐ and multi‐phase flows and heat transfer.

An overview is given of selected issues concerning the formulation of multidimensional models of two‐phase flow and heat transfer. A complete computational multiphase fluid dynamics (CMFD) model of two‐phase flow is presented, including local constitutive models applicable to two‐phase flows in heated channels. Results are shown of model testing and validation.

It has been demonstrated that the overall model is capable of capturing various local flow and heat transfer phenomena in general, and the onset of temperature excursion (CHF) in low quality forced‐convection boiling, in particular.

Whereas the multiphase model formulation is applicable to a large class of problems, geometries and operating conditions, the closure laws and results are focused on forced‐convection boiling in heated channels.

The proposed approach can be used to predict multidimensional velocity field and phase distribution in two‐phase flow devices and components used in thermal power plants, nuclear power plants and chemical processing plants.

A complete mechanistic multidimensional model of forced‐convection boiling in heated channels is given. The potential of a CMFD approach is demonstrated to perform virtual experiments that can be used in system design and optimization, and in safety analysis.

The oil, flux, and solder added to a hot air solder leveling tool creates an emission of oil mist, acidic gases, and solid metal compounds. The oil tends to form into very fine droplets, resulting in exhaust opacity. Diffusion type fiber bed filters are the optimal choice for the removal of oil mist. For optimal filter efficiency the exhaust stream should be cooled. A wet scrubber upstream of the filter will cool the exhaust stream through water evaporation. Additionally, the scrubber will remove acid vapor and coarse solids from the exhaust. The characteristic quality of a coalescing fiber bed filter is its ability to continuously drain liquid. The defining parameter in the service life of a fiber bed filter is the solids in the exhaust stream. These solids can lodge in the fibers and block a portion of the void area, and hence increase the filter pressure drop. In an attempt to extend filter life, a study was conducted for the use of detergents to clean the filter. These studies show that a detergent can extend filter life in the H.A.S.L. application by removing a blocking agent from the filter. Further tests are planned at additional locations to examine the performance at sites that use other ingredient formulations in the flux, oil, and solder.

To accurately predict transient flow in homogeneous gas‐liquid mixtures in rigid and quasi‐rigid pipes, two mathematical models based on the gas‐fluid mass ratio are presented. The fluid pressure and velocity are considered as two principal dependent variables and the gas‐fluid mass ratio is assumed to be constant. By application of the conservation of mass and momentum laws, non‐linear hyperbolic systems of two differential equations are obtained and integrated numerically by a finite difference conservative scheme. The fluid density is defined by an expression averaging the two‐component densities where a polytropic process of the gaseous phase is admitted. The rigid model is deduced by neglecting the liquid compressibility and the pipe wall elasticity against the gas deformability. The quasi‐rigid model takes into account these two parameters. The effect of fluid compressibility on transient pressure behaviour is then analysed and confronted to the pipe wall elasticity. Numerical solutions are compared with numerical results available in literature and experiment developed in the laboratory. The results show that the pressure wave propagation is significantly influenced by the gas‐fluid mass ratio and the elasticity of the pipe wall. They indicate that the pipe elasticity and liquid compressibility may be neglected for great values of gas‐fluid mass ratio but not for the smaller ones.