There are many examples of fluid flow simulation where it would be useful to have specified fluid sources located inside the computational grid. By “fluid sources” we mean a source of
fluid mass and momentum. Even more useful would be a capability where the location, flow rate, and flow direction of the fluid sources could be specified.
In this Technical Note, we describe a scheme that meets these goals in the FLOW-3D® program.
In the next section we describe the basic approach that was taken to add this capability and following that there are several examples illustrating the method.
A recent addition to FLOW-3D® is the ability to have full momentum coupling between a continuum fluid and discrete mass particles. This addition is described in the Flow Science
Technical Note FSI-99-TN50, “Particle-Fluid Coupling.” It is this capability that forms the basis of our addition for general fluid sources.
For purposes of discussion, suppose that we want to model fluid exiting the end of a pipe placed somewhere inside a computational grid. Fluid exits the end of the pipe with a specified flow rate
and flow velocity, i.e., both magnitude and direction are specified. In the most general case, the velocity distribution over the cross section of the pipe exit could be non-uniform. The location
of the pipe end should be arbitrary, so that moving the pipe by relocating it every time step in a transient computation would be possible.
To meet these goals, we imagine covering the end of the pipe with a set of particles. Each particle is assigned a mass source rate and a velocity corresponding to the fluid flow direction at
its location. We may think of these particles as representing average values of the flow for small areas surrounding them. In this sense, summing up the particles is equivalent to a numerical
integration of the flow over the cross section of the pipe. The particles simply represent the discrete elements of the integration area.