Multiphase Flow Theory Research Articles

Pressure wave propagation in high viscous magma containing crystals and bubbles

The presence of bubbles and crystals in highly viscous liquid (e.g., glass, magma) has been important for the purpose of both basic and practical viewpoints. In this presentation, especially, we focus on a magma, and investigate theoretically P-wave (i.e., pressure wave) propagation in the magma containing many bubbles. Based on an averaged theory of dispersed multiphase flow, we can regard the mixture of crystals (i.e., solid phase) and melt (i.e., liquid phase) as a single liquid phase, i.e., single non-Newtonian liquid, which is approximated to a Newtonian liquid by using the concept of an effective viscosity composed of various parameters (especially crystals). The system of basic equations for multiphase flow containing the effective viscosity, can be reduced to the KdV-Burgers equation as a nonlinear evolution equation via theoretical approximation based on singular perturbation method. As a result, the effect of fraction of crystals and bubbles on the acoustic characteristics (e.g., waveform evolution, nonlinearity, attenuation) is discussed.

Computational Fluid Dynamics Study on Bottom-Hole Multiphase Flow Fields Formed by Polycrystalline Diamond Compact Drill Bits in Foam Drilling

High-temperature geothermal wells frequently employ foam drilling fluids and Polycrystalline Diamond Compact (PDC) drill bits. Understanding the bottom-hole flow field of PDC drill bits in foam drilling is essential for accurately analyzing their hydraulic structure design. Based on computational fluid dynamics (CFD) and multiphase flow theory, this paper establishes a numerical simulation technique for gas-liquid-solid multiphase flow in foam drilling with PDC drill bits, combined with a qualitative and quantitative hydraulic structure evaluation method. This method is applied to simulate the bottom-hole flow field of a six-blade PDC drill bit. The results show that the flow velocity of the air phase in foam drilling fluid is generally higher than that of the water phase. Some blades’ cutting teeth exhibit poor cleaning and cooling effects, with individual cutting teeth showing signs of erosion damage and cuttings cross-flow between channels. To address these issues, optimizing the nozzle spray angle and channel design is necessary to improve hydraulic energy distribution, enhance drilling efficiency, and extend drill bit life. This study provides new ideas and methods for developing geothermal drilling technology in the numerical simulation of a gas-liquid-solid three-phase flow field. Additionally, the combined qualitative and quantitative evaluation method offers new insights and approaches for research and practice in drilling engineering.

Numerical and experimental study on water-sediment flow in a lateral pumping station forebay

Multiple vortex flow patterns are commonly observed in lateral pumping station forebays, particularly in basins with high sediment concentrations. These patterns can lead to pump blockage, sediment deposition, and other issues that disrupt pump station operations. The water-sediment two-phase flow in lateral pumping station forebays is significantly influenced by the start-up combination, yet our understanding remains limited. To address this, the mixture multiphase flow theory is introduced to describe water-sediment dynamics, and the mathematical model is validated with experimental data. By analyzing the characteristics and formation mechanisms of large vortex and multiple small vortex regions in the original scheme, nine different start-up combination schemes were proposed. The research results indicate that, due to the narrow channel and slope effect in the lateral forebay, some of the gravitational potential energy of the water-sediment mixture is converted into kinetic energy upon entering the forebay, thereby increasing the velocity in the main flow area. Additionally, due to the friction and dissipation effects of the two sidewalls, a pressure difference is generated in the main flow area, resulting in the formation of multi-level vortices. Furthermore, the various types of proposed start-up combinations can optimize the flow patterns in the forebay to a certain extent. The preferred scheme improved the uniformity of flow velocity by 18.63% and increased the deviation angle by 17.62°, resulting in a 75.47% reduction in vortex area compared to the original scheme. These research results provide theoretical guidance for optimizing start-up combinations and reorganizing flow field structures to achieve hydrodynamic dredging effects.

Effect of Entrainment on the Liquid Film Behavior in Pipe Elbows

Multiphase flow entrainment in natural gas engineering significantly influences the safety and efficiency of oil companies since it affects both the flow and the heat transfer process, but its mechanisms are not fully understood. Additionally, current computational fluid dynamics (CFD) methodologies seldom consider entrainment behavioral changes in pipe elbows. In this article, a verified CFD method is used to study the entrainment behavior, mechanism, and changes in an elbow. The results show that droplet diameter in a developed annular flow follows a negative skewness distribution; as the radial distance (from the wall) increases, the fluctuation in the droplets becomes stronger, and the velocity difference between the gas and the droplets increases linearly. Turbulence bursts and vortices sucking near the wall jointly contribute to droplet entrainment. As the annular flow enters the elbow, the secondary flow promotes the film expansion to the upper and lower parts of the pipe. Droplets re-occur near the elbow exit intrados, and their size is much smaller than those in the upstream pipe. Vortices sucking under low gas velocity play an important role in this process. These findings provide guidelines for safety and flow assurance issues in natural gas production and transportation and bridge the gap between multiphase flow theory and natural gas engineering.

Supercritical carbon dioxide heat transfer in horizontal tube based on the Froude number analysis

Supercritical carbon dioxide heat transfer in horizontal tube based on the Froude number analysis

Intelligent Inversion Analysis of Drilling Gas Kick Characteristic Parameters and Advanced Predictions of Development Trends

Summary Gas kicks are a common and complex occurrence in oil and gas exploration and development. Obtaining the characteristic parameters promptly and accurately after a gas kick occurs is of utmost importance. The kick characteristic parameters are essential foundational data for accurately understanding the multiphase flow state within the wellbore, analyzing kick development trends, and formulating well-killing design. Traditional methods for determining gas kick characteristic parameters often involve trial estimation, a process that can introduce significant arbitrariness. Alternatively, using specialized equipment for measurement and analysis is an option, but it can be time-consuming and limited by technology and cost constraints. This paper proposes an intelligent inversion method for kick characteristic parameters based on surface logging data, including standpipe pressure and mud pit volume. First, a gas kick simulation model is developed based on wellbore multiphase flow theory. This model can accurately simulate the changes in surface logging parameters that occur when a gas kick occurs. Next, the particle swarm optimization algorithm is used to optimize the kick parameters, such as the gas-influx index and pore pressure, in conjunction with the gas kick simulation model. The optimization evaluation criterion is the Fréchet distance, which is used to identify the calculated curve that is most similar to the actual logging parameter change curve. Subsequently, kick trends can be predicted using the simulation model based on these kick parameters. The case analysis demonstrates that the method proposed in this paper can rapidly acquire the gas kick characteristic parameters based on the early change characteristics of logging parameters. It effectively simulates and reproduces the true distribution of wellbore fluids, enabling advanced prediction of kick development. This approach helps in preparing preventive measures in advance, reducing the risk of accidents, and minimizing financial losses.

Numerical study of chain-reaction implosions in a spatial array of ceramic pressure hulls in the deep sea using a compressible multiphase flow model

Ceramic pressure hull arrays, which are core components in providing buoyancy to underwater vehicles, are at risk of chain-reaction implosions in deep-sea environments. This study establishes a numerical model for the chain-reaction implosions of ceramic pressure hull arrays. The model is based on the theory of compressible multiphase flow. The structural finite element method combined with the ceramic material failure criterion is used to determine the cause of chain-reaction implosions. Adaptive mesh refinement is adopted to capture the gas–liquid interface accurately. The accuracy of the numerical simulation method for compressible multiphase flow is verified through an implosion experiment involving a single ceramic pressure hull. Subsequently, the simultaneous implosions of an array of ceramic pressure hulls are calculated and investigated. Finally, the chain-reaction implosions of an array of ceramic pressure hulls are calculated using the proposed model. The propagation of the implosion shockwaves and the implosion flow field distribution are analyzed and compared with those of the simultaneous implosion case. The pressure reduction in the flow field caused by the expansion waves of the implosion is found to cause the chain-reaction implosion of neighboring ceramic pressure hulls. In the chain-reaction process, the air converges at the array center, and the implosion shockwaves converge toward the center and overlap, resulting in the largest-amplitude implosion shockwave occurring near the center of the array. This phenomenon is named the converging effect of chain-reaction implosions.

Design of Riser System Based on Target Oilfield and Platform

Abstract: Risers are an important component in the development of offshore oil and gas resources, but they are also one of the weakest components. Therefore, the safety of the design of deep-water riser systems plays a crucial role in the development of offshore oil and gas resources. This article focuses on the selection and initial design of riser systems based on the target oilfield and platform. Taking into account both the transportation capacity of oil and gas pipelines and the strength of casing, multiphase flow theory is used to calculate the pressure drop and transportation capacity of the riser. Based on this, the size of the oil pipe and casing is iteratively calculated. The riser design is based on the specifications and professional software Orcaflex, which is mainly used in the design process, is used for stress analysis of the riser, Taking into account the main scale of the FWPSO platform, reservoir and wellhead data, as well as the marine environment data where the riser is located, the selected oil and casing will be subjected to wall thickness design verification.

Advective gas flow in bentonite: Development and comparison of enhanced multi-phase numerical approaches

Advective gas flow in bentonite: Development and comparison of enhanced multi-phase numerical approaches

Multi-Physics Investigations on the Gas-Powder Flow and the Molten Pool Dynamics During Directed Energy Deposition Process

Abstract In order to establish a high-fidelity mechanism model for investigating the molten pool behaviors during directed energy deposition (DED) process, a molten pool dynamics model combined with the discrete element method is developed in the present study. The proposed model contains several newly added particle sources to further intuitively reproduce the interaction between the discrete powder particles and the molten pool. Meanwhile, the effects of the nozzle structure, carrier gas, and shielding gas on the feedstock feeding process are simulated in detail using the gas-powder flow model based on the multi-phase flow theory. The gas-powder flow model is used to provide the reasonable outlet velocities, focal distance, and radius of the focal point for the particle sources in the molten pool dynamics model, which solves the difficulty that the motion state of the powder streams obtained by the molten pool dynamics simulation is hard to reproduce the actual situation. Besides, relevant experiments are conducted to verify the developed models. The predicted parameters of the powder streams are consistent with the experiment, and the deviations of the predicted molten pool dimensions are less than 10%. The heat and mass transfer phenomena inside the molten pool are also revealed. Furthermore, the maximum size of the spherical pore defects is predicted to be 18.6 µm, which is underestimated by 7% compared to the microscopic observation. Altogether, the numerical methods developed in this study could further augment and improve the samples for the machine learning modeling of DED process.

Numerical simulation and analysis of the chain-reaction implosions of multi-spherical hollow ceramic pressure hulls in deep-sea environment

Numerical simulation and analysis of the chain-reaction implosions of multi-spherical hollow ceramic pressure hulls in deep-sea environment

Optimizing embankment structures in a snowy permafrost region of the pan-Arctic based on a coupled numerical model

• A numerical model considering snow drift is developed for the permafrost embankment. • Increasing the embankment height may accelerate the permafrost degradation. • A UCRE is designed to address the permafrost degradation caused by snow accumulation. In pan-Arctic permafrost regions, snow drift may lead to more snow accumulation around the road, which prevents the heat release from the underlying soil in winter and aggravates the permafrost degradation beneath the road. However, the study of snow distribution pattern around the road is insufficient, which makes it difficult to accurately evaluate the long-term stability of the road. To investigate the thermal regime of the road and optimize the road structure in permafrost regions under the effect of snow drift, based on heat transfer and multiphase flow theories, a coupled numerical model is presented. The model includes the snow transportation around the embankment, natural convection of air in the crushed-rock layer, and heat conduction with phase changes in soil and snow layers. Results of model simulation show that an embankment with a height of 4 m leads to heavier snow accumulation on both sides of the embankment in winter compared to an embankment with a height of 3 m, which accelerates permafrost degradation. The full crushed-rock embankment with a height of 3 m can be used to mitigate the permafrost degradation caused by snow accumulation on both sides of the embankment to some extent. By contrast, when the U-shaped crushed-rock embankment (UCRE) with a height of 3 m and a 1:6(vertical: horizontal) gentle slopes is used, the snow accumulation around the embankment is greatly reduced, the embankment slope delivers better cooling performance. Considering the climate warming at a rate of 0.067 ℃ year-1 in pan-Arctic regions, the thermal stability of UCRE can still be guaranteed after 20 years of its construction. These results provide a valuable reference for road construction in pan-Arctic permafrost regions.

The flow patterns and sediment deposition in the forebay of a forward-intake pumping station

In Northwest China, the concentration of sediment in the Yellow River is high. The flow patterns in the forebay and inlet tank of a pumping station on the river are disordered, and sediment deposition endangers the normal operation and safety of the pumping station. To address this problem, the three-dimensional two-phase water–sediment flow in the forebay of the pumping station is modeled using fluid simulation software, and diagrams of the sediment content and velocity streamline in the flow layers of different sections are obtained. Combined with the multiphase flow theory of mixtures and the realizable k–ε turbulent kinetic energy equation, the location and formation mechanism of each vortex, as well as the area and degree of sediment deposition in the forebay, are analyzed. The actual engineering and numerical simulation results are compared to verify the accuracy of the simulation, and the operating conditions of each pump port under different unit operating conditions are proposed. The results show that the deposition of sediment has different effects on the outlets of the pumps, but its impact on pump Nos. 4, 5, and 6 is small. After desilting, the velocity uniformity and deflection angle of pumps 4, 5, and 6 are improved to a certain extent. This study provides specific guidance for the construction and reconstruction of a pumping station forebay to avoid the impacts of backflow areas and sediment deposition to a certain extent.

Numerical simulation of snowdrift on an air-supported membrane structure and response analysis under snow loads

The air supported membrane structure is a typical nonlinear flexible long-span space structure, the wind-induced drift and the resulting accumulation and distribution of snow particles on the structure may be the primary design concern among all loads in heavy-snowfall region. Thus, an accurate prediction of snow distribution on membrane surface is vital to structural design. A numerical simulation method is used to estimate snowdrift in this paper. Based on Euler-Euler method in multi-phase flow theory, this numerical model adopted Mixture model and combined with the snow deposition and erosion model, the snowdrift on an air-supported membrane coal shed is simulated, the distribution factor for roof snow load is given under different wind speed and different directions to estimate the worst load case, snow load on the air-supported membrane structure is significantly affected by snowdrift which causes significant non-uniform snow load. Furthermore, the response analysis of the air-supported membrane structure under snow load is studied, for comparison, uniform snow load case, non-uniform snow load case, and simulated snow load case under 0° wind direction are all considered. The results show that non-uniform snow load caused by snow drifting is more dangerous and should be considered.

Effects of Water and Fertilizer Flow Rates on the Mixing Process and Fertilization Uniformity of Cotton under Mulch Drip Irrigation

Water and fertilizer flow rates are the most convenient variable to control in the process of drip irrigation under mulch. Suitable water and fertilizer flow rates are beneficial to improve water and fertilizer uniformity. Nine groups of water and fertilizer rate combinations were set in the common water and fertilizer rate range to study the influence of the water and fertilizer rate on fertilization uniformity. The numerical simulation of the mixing process in the main pipe was first carried out based on the multiphase flow theory, and then the field experiment for the different water and fertilizer rate combinations in the machine-picked cotton-planting pattern (one film, three tubes and six rows) was conducted. Through the numerical simulation of the mixing process in the pipeline and the analysis of water and fertilizer uniformity field experiment results, it was found that the uniform mixing length is related to the water and fertilizer flow rate, and the water and fertilizer flow rate had some effect on fertilizer uniformity. In the irrigation system with a main pipe diameter of 100 mm and a fertilizer injection pipe diameter of 20 mm, the water fertilizer flow rate ratio should be between 3–8 to ensure the effect of the mixing process and fertilization uniformity. A water flow rate of 2 m s−1 and fertilizer flow rate of 0.35 m s−1 is recommended during the fertilizer process in northern Xinjiang. This paper shows the feasibility of numerical simulation in the study of cotton water and fertilizer mixing processes, and the results can provide some reference for cotton planting.

Numerical simulation and analysis of the underwater implosion of spherical hollow ceramic pressure hulls in 11000 m depth

Pressure hulls play an important role in deep-sea underwater vehicles. However, in the ultra-high pressure environment, a highly destructive phenomenon could occur to them which is called implosion. To study the characteristics of the flow field of the underwater implosion of hollow ceramic pressure hulls, the compressible multiphase flow theory, direct numerical simulation, and adaptive mesh refinement are used to numerically simulate the underwater implosion of a single ceramic pressure hull and multiple linearly arranged ceramic pressure hulls. Firstly, the feasibility of the numerical simulation method is verified. Then, the results of the flow field of the underwater implosion of hollow ceramic pressure hulls in 11000 m depth is analyzed. There are the compression-rebound processes of the internal air cavity in the implosion. In the rebound stage, a shock wave that is several times the ambient pressure is generated outside the pressure hull, and the propagation speed is close to the speed of sound. The pressure peak of the shock wave has a negative exponential power function relationship with the distance to the center of the sphere. Finally, it is found that the obvious superimposed effect between spheres exists in the chain-reaction implosion which enhances the implosion shock wave.

Application of multiphase flow and droplet separation theory in modeling cough droplets contamination range to mitigate COVID-19 transmission: Do not stand too close to me!

On March 11, 2020, the World Health Organization (WHO) declared that COVID-19 is a pandemic, warning the world of a health catastrophe and social, economic, and political disruptions. According to WHO, COVID-19 is transmitted by the transport of respiratory droplets generated by a violent respiratory event such as sneeze and cough directly to susceptible persons, or indirectly through surfaces. The aim of this study is to propose simple physical and mathematical models based on two-phase flow dynamics and droplet separation theory. The proposed mathematical model predicts the contamination range of ejected cough droplets, estimating the safe person-to-person social distance. As a result, the proposed simple model predicted a contamination range of 2.3 m for a male adult. In addition, to understand the behavior of ejected cough droplets, a sensitivity analysis is carried out to investigate the effect on contamination range of cough air flowrate, i.e., body/lung size, droplet size, and droplet drag coefficient. It is found that as the body/lung size decreases, i.e., lower cough flow rate, contamination range decreases, resulting in 1.9 m for an adult female, and 1.4 m for a child. In addition, the model predictions show an appreciable effect of droplet size, and droplet drag coefficient on cough contamination range. In particular, the effect of droplet drag coefficient is of interest, because of its relationship to ambient conditions such as temperature and relative humidity, in which both affect ambient air viscosity, and thus drag coefficient. This is important in investigating the contamination range and person-to-person social-distance as climate changes.

Water film area and dust removal efficiency of string grilles: a theoretical analysis

Based on multiphase flow theory and capillary mechanics, the dimensionless bond number expression of the influence of string grille wire spacing on droplet spreading is derived. Taking a liquid film formed by spreading droplets based on Kelvin correlation, the Young–Laplace equation, and the Hagen–Poiseuille law, an equation for calculating the thickness and height of the liquid film is established with temperature, relative humidity and molar volume of liquid phase as independent variables. According to the theory of string grille filtration and dust removal, a dust removal efficiency calculation model covering the wet string grille wire group is constructed based on the liquid film thickness, height, wire diameter, water film area, and vortex shedding frequency. Finally, a theoretical analysis of the influence of water film area on the efficiency of wet string grille dust removal is carried out based on the spray pressure and the ratio of string grille wire distance to wire diameter. It is found that the effect of spray pressure on water film area and dust removal efficiency is more significant than the string grille wire distance diameter ratio. Moreover, the optimized combination of wet string grille wire distance diameter ratio 0.84, wind speed 3 m/s and spray pressure 0.8 MPa is found, which could provide an important reference for engineering applications.

Numerical investigation on fluid dynamic characteristics around shoulder ventilation of submarine-launched vehicle

In order to study the influence of the ventilating cavitation flow at the shoulder of a submerged-launched vehicle on the surface hydrodynamic characteristics, a three-dimensional potential model for the shoulder ventilation of the vehicle was established based on the homogeneous multiphase flow theory, standard RNG k-ε model, Singhal cavitation model and overlapping grid technology, and the numerical simulation of the unsteady evolution process of the ventilated cavitation flow was carried out, and the cavitation flow morphology evolution, surface pressure distribution and resistance characteristics under different ventilation rates were compared. The results showed that the thickness and length of the ventilated cavitation flow in the early stage of fusion continue increased with the increasing of ventilation volume, and its thickness and length changed slightly in the later stage; when the exhaust position did not change and the ventilation volume was within a certain range, the differential pressure resistance coefficient and viscous resistance coefficient decreased with the increasing of internal pressure of the ventilated cavity.

Influence of Cutting Tools on Filter Cake Formation during Slurry Shield Tunnelling

The filter cake on excavation face would be destructed periodically by cutting tools during slurry shield tunneling. The broken filter cake has a risk for face stability. The influence of cutting tools on filter cake was studied in this paper. A slurry-soil interaction model based on a multiphase flow theory which considers the solid particles and fluid in slurry was developed. The whole process of slurry penetration and filter cake formation on the excavation face of slurry shield can be described by this model. The motion state of cutting tools can be combined with this model and the effect of cutting tools on the slurry-soil interaction and pressure transfer mechanism was analyzed. Subsequently, the comparative calculations were presented to discuss the influence of tunneling parameters and the design of cutting wheel on filter cake formation during slurry shield tunnelling. The results indicate that the total area of filter cake on excavation face increases with the decreasing of revolutions per minute of cutting wheel and shield machine advance rate. The area ratio of filter cake on the center of excavation face always larger than other zone due to the lesser amount of cutting tools within one track in the center of cutting wheel. The results can provide a better understanding of how to set the shield tunneling parameters and design the layout of cutting tools for the stability of tunnel face.