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  • Set up your own cloud-native simulation in minutes.

    • Documentation

    SimScale DocumentationAnalysis TypesMulti-purpose AnalysisMulti-purpose Multiphase

    Multi-purpose Multiphase

    The Multi-purpose solver can be a great choice if one wants to perform multiphase simulations involving the time-dependent behavior of two fluids using the VOF (Volume of Fluid) method.

    Animation 1: Water spillway in canal

    The VOF solver employs a proprietary, higher-order reconstruction scheme for the interface modeling, along with a robust binary tree-based mesher, which helps in fast mesh generation of complicated geometries and stable convergence over a wide range of problems.

    The following advantages make the Multi-purpose solver a great choice for multiphase simulations:

    Multiphase simulations are inherently transient. Hence, the Time dependency will switch to Transient when the Multiphase option is toggled on. One can also change the Time dependency to Transient first and then toggle on Multiphase. These can be done within the global settings for the Multi-purpose analysis.

    toggle Multi-purpose multiphase solver
    Figure 1: Toggling on the Multiphase feature within the Multi-purpose solver in SimScale

    The user needs to specify the number of phases involved in the multiphase simulation.

    Initial conditions define the values which the solutions fields will be initialized with. The phase fraction can be initialized globally or for a specific region as a subdomain for all the phases involved.

    Multi-purpose multiphase phase fraction initialization
    Figure 2: Phase fraction initialization inside a subdomain for multiphase simulations

    Phase fraction sum

    The solver will throw an error if the sum of the phase fractions does not add up to one. Please ensure the values of the associated phases add up to one under Initial conditions > Phase fractions > Subdomains.

    In multiphase simulations, boundary conditions and phase fractions are essential for accurately modeling how different phases interact. Boundary conditions define how fluids enter, exit, or interact with surfaces, ensuring realistic flow behavior. Phase fractions determine how much of each phase is present in different regions, affecting mixing, movement, and heat transfer.

    Inlet

    When defining inlet boundary conditions in a multiphase simulation, the phase fraction for each face must be specified by the user to ensure the correct distribution of phases entering the domain. Having the settings shown in Figure 3 means that the fluid defined as phase 1 will enter the domain at 100% phase fraction, meaning no presence of other phases at the inlet. It will enter with the specified velocity, such as 2 m/s in this example.

    Figure 3: Inlet boundary conditions showing 100% phase 1 entering the domain at a specified velocity of 2 m/s.

    In outlet boundary conditions, there are two main options: flow-driven and backflow. For a flow-driven outlet, no phase fraction input is required because the flow is determined by the simulation itself, and the fluid exits the domain without a need for phase definition. In contrast, when back flow is present, phase fraction input is necessary to account for the possibility of fluids flowing back into the domain, as shown in Figure 4. This ensures that the correct phase distribution is maintained when reverse flow occurs.

    Additionally, the hydrostatic pressure can be enabled to define the height at which the hydrostatic pressure profile is equal to the static pressure. Including hydrostatic pressure is particularly useful for marine applications because it accounts for the pressure variations due to changes in fluid height.

    Figure 4: Outlet boundary conditions with flow-driven and backflow options, including the hydrostatic pressure setting for depth-dependent pressure profiles.

    View the following validation case to understand the setup in a multiphase simulation:

    • AEC and Hydraulic engineering
      • Assess dynamic forces and free surface wave patterns on hydraulic structures like radial gates, tunnel chutes & spillways
      • Hydraulic design of stormwater drainage culverts & irrigation systems
      • Dam break analysis
      • Assessing approach conditions on pump sumps & inlet geometry effects on reservoir mixing
      • Open channel flows
    Animation 2: Flow visualization and forces on dam gates
    • Industrial equipment
      • 3D flow patterns and mixing efficiency in industrial mixers
      • Separation efficiency and phase fraction distribution in fluid separation systems
      • Mixing and air flow rate analysis in aeration beds
      • Design of desalination equipment (water-brine simulations)
      • Fluid behavior in venturi scrubbers and gas mixers
    • Rotating machinery
      • Performance analysis of hydraulic turbines 
      • Mixing efficiency and flow behavior in Rushton turbines, industrial mixers & stirred tank reactors  
      • Performance and flow analysis of liquid-gas flows through rotodynamic pumps in O&G, food processing, water transportation, etc. 
      •  Flow analysis and thrust computations for marine propellers
    Animation 4: Purging water-primed pump with the working fluid, oil
    • Flow control
      • Pressure drops and hydraulic loss assessment through subsea piping systems
      • Flow capacity assessment of multiphase mixtures through different types of valves
      • Tank filling and surge tank analysis
      • Fuel injectors, coolant flows through HVAC systems and oil-air flows through engine chambers
      • Flow rate and range analysis of fire fighting equipment
    Animation 5: Pressure and filling progress during the valve priming process

    Last updated: April 9th, 2025