Multiphase Flows

Chances are that your fluids simulation includes multiphase flows like boiling, cavitation, dispersed multiphase flows, immiscible flows and flows with particulates. ANSYS CFD provides the widest range of sophisticated turbulence and physical models to accurately simulate the toughest challenges so you can confidently predict your product’s performance.

Many fluids simulations include multiphase flows. Whether you are designing a super-fast transport and need to counter ice build-up, developing a blood enzyme test, delivering and melting rare metallic powder compounds for additive manufacturing, or designing a filtration system to provide clean drinking water in a remote location, you are solving multiphase problems.

As we push the boundaries to improve our products and processes, we need to gain a better understanding of how liquids, solids and gases interact. Each of these varied multiphase challenges requires a different modelling approach. Our customers have been using ANSYS CFD for over 40 years to achieve the widest range of accurate multiphase models and confidently predict their product’s performance. To truly understand your product, you must get your multiphase simulations right.

Fluent AIAD accurately simulates complex multiphase regime transitions like the air-water flow in this 180 degree pipe bend.
Read the Multiphase Flows application brief

All users can get great multiphase simulation results

With Fluent’s streamlined workflow, novice and expert users can set up complex multiphase simulations. A single, tabbed panel organizes multiphase setups into a logical, step-by-step flow that saves time. In a benchmark gas–liquid pipe flow simulation, the setup proved 25% faster and eliminated the need to access 17 scattered software places.

A single, tabbed panel organizes Fluent's multiphase setup into a logical, step-by-step flow that is 25% faster

Fluent AIAD model accurately simulates complex, multiphase regime transitions

Transitions between continuous stratified flows and dispersed flows are usually difficult to model. They frequently appear in nuclear reactors, oil and gas pipelines, steam generators, refrigeration equipment, reflux condensers, packed columns and heat pipes.

Fluent’s algebraic interfacial area density (AIAD) model accounts for differences in drag and interfacial area along the interface, depending on the flow morphology. A third phase may be added to capture a mass-transfer mechanism, to allow breaking of the continuous phase into a dispersed phase (via entrainment), and the dispersed phase into a continuous fluid phase (via absorption), for better accuracy.

When combined with a population balance model, the AIAD model provides detailed droplet size distributions of bubbles or droplets. This combination is well-suited for safety critical applications, including loss of coolant scenarios in pressurized water nuclear reactors. The Fluent model accounts for sub-grid scale turbulence associated with interfacial instabilities at the free surface, to more accurately predict counter-current flow limitation or flooding, which inhibits effective cooling.

Why Shallow Containers Slosh

To avoid severe load instabilities, engineers often face strict design requirements to control sloshing of liquid in moving containers, such as tanker trucks or rockets. In these applications, designers usually insert interior baffle plates or similar structures to impede the flow of liquid. Other application involving sloshing liquids include harbor design or the study of long-wavelength tsunami waves. In all these cases, simulation plays a key role in predicting sloshing and evaluating ways to solve the problem.

Alex helps us demonstrate sloshing. Analysis indicates that the first sloshing mode is 1.6 Hz,
the frequency at which the bowl is prone to resonance and spills its contents.

An example of sloshing is the carrying of a dog bowl full of water, in which the liquid has the tendency to slop from side to side and often spill. A multiphase simulation of this free surface flow reveals that this behavior occurs because the first sloshing mode of the bowl is roughly at 2 Hz — the typical human step frequency that excites this undesired resonance. Repeating the analysis for a glass of water reveals a first sloshing mode of 4 Hz, which shows why water glasses are much less prone to spilling than bowls. In these simulations, the structural walls have been assumed to be rigid. Engineers also can study sloshing in elastic vessels such as reactor containment structures using the fluid–structure interaction (link to FSI Application page) capabilities in ANSYS software.
By Marold Moosrainer, CADFEM

See ANSYS Multiphase Capabilities