Setting Up a Cavitation Phase Interaction

Create a phase interaction, select a cavitation model, and specify the appropriate model properties and material properties.

To set up a cavitation phase interaction:
  1. Create a phase interaction, and set the primary phase to the appropriate liquid phase, and the secondary phase to the appropriate gas phase.

    See Controlling Phase Interactions in VOF Simulations.

  2. In the Phase Interaction Model Selection dialog, in the Cavitation Models group box, select the cavitation model to use:
    • Full Rayleigh–Plesset (for single-component phases) or Multi-component Full Rayleigh–Plesset (for multi-component phases)

      Implements the full Rayleigh–Plesset equation, which includes the influence of bubble growth acceleration, as well as viscous and surface tension effects.

    • Schnerr-Sauer (for single-component phases) or Multi-component Schnerr-Sauer (for multi-component phases)

      Implements a reduced Rayleigh–Plesset equation, which neglects the influence of bubble growth acceleration, viscous effects, and surface tension effects.

    • Homogeneous Relaxation (for single-component phases) or Multi-component Homogeneous Relaxation (for multi-component phases)

      Implements a finite rate equation with an empirical time scale formulation, and is suitable for modeling phenomena which occur in thermal non-equilibrium.

    The selected cavitation model appears under the Multiphase Interaction > Phase Interactions > [phase interaction] > Models node.

The Schnerr-Sauer cavitation model is an approximation that is derived for idealized conditions. However, the specific conditions of your simulation can be less than ideal (for example, insufficient mesh and time resolution, unresolved bubble to bubble interactions and flow details).

If you want to move the simulation results for the Schnerr-Sauer cavitation model in a direction that matches observed experimental results, you can scale the bubble growth rate by specifying the appropriate scaling factors for positive and negative bubble growth rates. Using the positive scaling factors lets you increase the cavitation rate if, for example, the mesh is not fine enough to resolve sharp corners that consequently cause Simcenter STAR-CCM+ to underpredict the minimum pressure. Negative scaling factors also let you delay bubble collapse if, for example, the bubbles travel inside turbulent eddies where the local pressure is smaller than the average pressure that Simcenter STAR-CCM+ calculates. In this scenario, the bubble collapse is slower than predicted by the Schnerr-Sauer cavitation model.

  1. To scale the positive and negative bubble growth rates for the Schnerr-Sauer cavitation model, expand the Schnerr-Sauer node or the Multi-component Schnerr-Sauer node and specify the scaling values in the ScalingFac+ and ScalingFac- child nodes.

    The scaling factors are always positive and are independent: you can set either or both, as appropriate to your simulation.

    See Cavitation Model Child Nodes.

For multi-component phases, the Connectivity property of the cavitation model lets you select the gas component that corresponds to each liquid component.
  1. Select the Multi-component Schnerr-Sauer node, the Multi-component Full Rayleigh-Plasset node, or the Multi-component Homogeneous Relaxation node and set the Connectivity property to map the components in the liquid phase to their corresponding components in the gas phase.

    For cavitation models, you can ignore the dissolved gas components of the liquid mixture. To ignore a particular component of the liquid mixture, set the corresponding gas component to None.

    See Cavitation Model Family Properties.

    The equilibrium coefficient for liquid components in a cavitation simulation is found using Raoult’s Law. There are no Equilibrium Coefficient values to set.

The Homogeneous Relaxation model requires further property settings.
  1. Select the Homogeneous Relaxation node or the Multi-component Homogeneous Relaxation node and set the following properties:
    • Time Scale Modeling Constant
    • Void Fraction Exponent
    • Dimensionless Pressure Exponent

    See Homogeneous Relaxation Model Properties.

Many phase change processes can be described as bulk processes that start from certain seeds (imperfections that act as nuclei). Simcenter STAR-CCM+ uses a homogeneous approach, which is based on the presence of seeds and their subsequent growth and collapse as bubbles. This assumption is used to calculate an appropriate mass transfer rate that is based on the material and thermodynamic properties of the entire control volume [604].

The seed density and seed diameter are specified for each phase interaction, and not per rate model.

This step applies to the Schnerr-Sauer cavitation model and the Full Rayleigh-Plasset cavitation model only.

  1. Under the [phase interaction] > Models > Multiphase Material > Material Properties node, set the Seed Density and Seed Diameter values.

    If multiple rate models use the same phase pair, for example simultaneous cavitation and gas dissolution between a liquid and a gas, the results are consistent. That is, the local radius of the bubbles cannot be different depending on which rate model is used.

    If you use two different phase interactions, between the same two phases, for modeling cavitation and dissolution, you can specify the seed properties individually for each phase interaction. This option allows you to tune the models, but in a manner that is inherently inconsistent.

    See Cavitation Model Material Properties.