Initial conditions define the starting values for each solution field. They play a vital role in the stability and computing time for steady-state simulations, and are important for getting physically accurate results in transient analyzes. Therefore, it is very important to define appropriate initial conditions for your simulations.
Uniform initialization assigns the prescribed value for a variable over the complete domain as the initial condition before the beginning of the simulation.
Depending on the type of field to be initialized, the value can be a scalar or vector.
For steady-state flow simulations, it is recommended to set the value close to the expected solution to enhance the convergence behavior.
For multi-phase flows, a uniform phase-fraction would mean that the complete domain/mesh is initially (before the beginning of the simulation) filled with the fluid material assigned to the specified phase (either 0 or 1).
In addition to a uniform initialization of the variable over the domain, the subdomain-based initialization allows users to initialize a field in a specific region of the domain called a sub-domain.
A sub-domain can be defined using a geometry primitive or by assigning a volume regions.