Inlet and outlet boundary conditions

boundary conditions

There are typically two sets of main boundary conditions in CFD studies – inlet, and outlet conditions. These are usually surfaces, to which a constant value is usually applied (flow velocity or pressure, for example).

1D data can plug very simply into this, by linking one of the 2 boundary conditions to a corresponding variable from the 1D simulation. This will apply it to the whole surface as a zero-gradient boundary condition zero-gradient boundary condition , and provide the CFD software package with a realistic boundary condition to use during that particular time-step of the simulation.

Figure 25: Meshing regions and boundary conditions in CFD

Another way of taking advantage of 1D results is by using them as parameters in a moving-mesh configuration. Non-stationary CFD studies involving geometries where part of the geometry can be moved are becoming more and more common-place. Examples of this are for instance compressor wheels in fans and pumps, which are in rotation, or injectors where needles are in movement, displacing the plunger which carries out the injection by squeezing out the fuel.

Figure 26: Needle lift is a variable that can be used to pilot moving-mesh parameters in a CFD simulation [1]

Simcenter Amesim makes it possible to make the most out of both fixed and moving mesh moving mesh  CFD studies, thus also accommodating dynamic simulations for components with variable geometries.