Smoothed-Particle Hydrodynamics (SPH)
Smoothed-Particle Hydrodynamics (SPH) is a numerical method that overcomes the volume meshing-related constraints occurring with mesh-based models. SPH represents the fluid as a collection of particles with material properties that move with the fluid, making it well-suited for applications with highly dynamic free-surface flows.
The distinct characteristic of the SPH approach is that it models flow development without the need for a volume mesh. Instead, with SPH, the fluid is discretized into dynamic elementary points, referred to as particles, without predefined connectivity between them. A fundamental concept in SPH is the kernel (smoothing) function, which considers the influence of neighboring particles on one another within a specified radius.
The SPH model uses surface regions to represent the computational domain and only the surface mesh is required for the flow to interact with. Boundary interactions are simulated by using ghost particles—introduced on the boundary surface to represent the impact of the physical boundary on the fluid.
The SPH model in Simcenter STAR-CCM+ uses phase models to define the liquid particles. Particle size (discretization length) defines the spacing of the particles in the fluid domain, while particle volume discretization is performed by partially or fully filling the fluid domain volume with discrete particles.
In SPH, the free surface is defined by the Lagrangian framework of particles. Zero pressure is enforced at the free surface due to the absence of particles in the gas phase, eliminating the need for explicit free surface definition. Any point with an incomplete neighborhood is then automatically identified as near the free surface.
SPH is particularly well-suited for fast dynamic flows and complex boundaries, including interfaces with fragmentations and reconnections such as breaking waves, jets and splashes, and moving parts.
Considerations for the Smoothed-Particle Hydrodynamics (SPH) model
When setting up a simulation that uses SPH, take the following points into consideration:
- The SPH model uses a prediction-correction method for velocity and pressure, with preconditioning to enhance the convergence of the solution method. You are advised not to deactivate preconditioning to avoid difficulties with convergence of the iterative schemes. The scheme sets the default value for the maximum inner iterations stopping criterion to one, as it uses a single inner iteration for the prediction-correction method.
- In SPH, the working pressure is equal to the static pressure. The pressure field function is defined for both particles and boundaries, while static pressure is defined on boundaries only. The reference pressure is automatically set to achieve a static pressure of 0 Pa at the free surface and cannot be modified.
- You are advised not to update the surface region or modify the boundary parts selection on a running or completed SPH simulations. This action is not supported by Simcenter STAR-CCM+ and such modifications will reset the fluid (and ghost) particles to their initial state.
- When running SPH simulations, you are advised to choose a suitable output frequency to prevent your simulation from slowing down, in particular when exporting the volume fractions at the boundaries.