Applications and Prospects of Multiphase Flow in Simulation
Whether designing de-icing systems for hypersonic vehicles, conducting blood enzyme tests, transporting and melting rare metal powder compounds for additive manufacturing, or configuring filtration systems in remote areas to provide clean drinking water, engineers need to consider interactions between liquids, solids, and gases. In these diverse multiphase flow applications, each simulation requires different modeling approaches.
Accurate multiphase flow simulation depends on precise prediction of mechanical, thermal, and chemical interactions between phases. However, observing these physical processes is costly or even inaccessible. Today, engineers can rely on multiphase flow modeling and simulation technologies to gain insights into factors that improve efficiency, yield, safety, and reliability.
Multiphase flow simulation can visualize flow patterns that vary with location. For example, the flow pattern at the bottom of an oil and gas well may be entirely single-phase liquid, but as the height increases, bubbles gradually form, and the flow pattern transitions to a multiphase state. Therefore, in such physical processes, different locations require different multiphase flow models.
Multiphase flow simulation is more challenging than single-phase flow simulation. A complete description of multiphase flow requires solving mass, momentum, and energy equations for each phase, as well as interactions between phases. Due to the diversity of physical phenomena and the possibility of multiple flow patterns coexisting, reasonable simulation of phase interactions becomes crucial.
Free surface flow involves two or more immiscible fluids, each assumed to be continuous in most of the flow domain. Each fluid has distinct, identifiable flow regions whose shapes and positions change over time. These regions are large enough to be covered by multiple grid cells in the Volume of Fluid (VOF) model, which solves for the shape and position of interfaces between phases.
Applications include: ship motion in water, dam breaks, fuel tank sloshing, stratified flow, slug flow (large bubbles passing through liquid in pipes), and droplet breakup at inkjet printer nozzles.
VOF model usage: The VOF method uses a single fixed grid covering the entire flow domain to calculate the motion of each phase, local volume fractions, and the shape of interfaces between phases. At any spatial point, only one fluid phase exists, and there is typically only one velocity field to solve. However, in cases with large velocity differences along the interface, solving two separate velocity fields can improve computational robustness and accuracy.
Various interface tracking methods have been developed, each balancing computational accuracy, speed, and numerical robustness.
In discrete multiphase flow, there is one continuous phase and one or more discrete phases.
The discrete phase consists of many small discrete droplets, bubbles, or solid particles distributed throughout the continuous phase. Typically, these particles are much smaller than the flow domain and often smaller than the cell size.
The large number of particles makes it impossible to calculate the motion of individual particles. Thus, the Eulerian and Lagrangian methods—two common approaches—are used to simulate such discrete particle systems.
The Eulerian method describes the fluid-particle system as a mixed continuous phase and solves mass, momentum, and energy equations for each phase.
Trajectories of droplets, bubbles, or particles are not calculated individually.
Motion equations include solving for drag forces between phases and other relevant forces in discrete multiphase flow systems.
Results typically include local velocity, temperature, and volume fraction of each phase.
Interface shapes are not calculated separately.
Variants of the Eulerian multiphase model: When velocity differences between phases are relatively small, the model can be simplified by solving only one mixture motion equation (instead of equations for each phase). The model can include breakup and coalescence of bubbles or droplets to calculate their size distribution. For solid particles in liquids or gases, the Eulerian-granular model can account for particle collisions, friction, and the effects of packing density.
The Lagrangian particle tracking method calculates trajectories of individual particles, particle packets, droplets, or bubbles in the continuous phase. It is also known as the Discrete Phase Model (DPM).
In practice, this method is suitable for scenarios where the volume fraction of particles or droplets is small—typically less than 10%.
If the total number of particles is too large to calculate, the model can be simplified by tracking only statistically significant particle packets.
The impact of particles on the continuous phase can be evaluated (and vice versa).
Mass transport effects such as evaporation, condensation, and chemical reactions (e.g., combustion) can also be simulated.
The Dense Discrete Phase Model (DDPM) and Discrete Element Method (DEM) are used to simulate granular flow.
Multiphase flow calculations can be steady-state or transient.
Steady-state calculations are suitable for physical processes where the final result is independent of initial conditions and there are significant differences in phase inlet boundaries. Most other multiphase flow phenomena are modeled as time-dependent processes. Multiphase flow simulation is computationally intensive due to additional equations and transient calculations. Efficient parallel computing methods, such as those offered by boyfea (博业), help keep multiphase flow model calculations within reasonable timeframes.
Despite the powerful capabilities of today’s multiphase flow simulation, engineers continue to push its boundaries.
They are integrating and simulating more physical models: physicochemical reactions, moving objects, high speeds, size changes, phase transitions, and heat exchange, while addressing larger-scale physical systems. For example, an energy producer simulated an oil-water gravity separator with over 1 billion grid cells.
Beyond oil and gas, multiphase flow simulation is increasingly applied in industries such as chemicals, power, automotive, aerospace, and marine engineering.
For instance, swimwear manufacturer Speedo used multiphase flow simulation to optimize goggle design. Due to the small size of droplets relative to the swimmer’s body, goggle simulation required high-precision grids to capture droplet forces. A water film thickness of at least 10 grid cells was needed for resolution, leading to a sharp increase in total grid count.
To optimize energy efficiency and water usage in automatic dishwashers, engineers used multiphase flow and multiphysics simulation to model various flow pattern changes: jets from nozzles on rotating arms, water film formation as jets splash onto dishes, liquid films or droplets sliding off dishes, and water pooling under rotating arms. They used the Lagrangian method to simulate the complete motion of water jets and droplets from rotating arms to dishes.
The Lagrangian film model accurately simulated film formation on dishes impacted by jets, calculating film thickness, coverage, and the influence of arm design factors.
The VOF model simulated gravity-driven flow and the sliding down of liquid films/droplets into the sump at the bottom of the dishwasher.
Evaporation and condensation models simulated the drying process.
Multiphase flow simulation of the automatic dishwasher is part of a complete multiphysics system simulation. boyfea , as a professional CAE solution provider, offers comprehensive support for such integrated simulations, covering model creation, structural optimization, and multi-physics coupling analysis to enhance design efficiency and reliability.
As a leading CAE application solution expert in China, boyfea provides enterprises with fast, accurate, and comprehensive CAE application solutions, including CAE software secondary development, CAE technology implementation and application, and CAE technical consulting and training. With decades of experience, boyfea has successfully provided customized CAE simulation solutions for over 1,000 enterprises across industries such as aerospace, shipbuilding, ordnance, nuclear power, electronics, automotive, machinery, and electricity. Choose boyfea to unlock unlimited possibilities for your enterprise.
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