Application Note: Making History

Flow simulations are often undertaken to determine the history of a flow process. For example, how much air is entrained in an open channel flow and where does it go? Other examples include: How effectively can a chemical reaction occurring at a gas-liquid surface be mixed into the bulk of the liquid? And where are there likely to be defects in a metal casting because of air entrapments metal fills a mold?

Many of these history questions can often be answered simply by defining scalar agents to collect and record the necessary data. A properly designed agent can provide detailed information in a concise way that saves an user from having to painfully sort through extensive data files. The flexibility of "history" scalars is evident when one realized that they can be limited to fixed locations, moved with a fluid, or allowed to mix into a body of fluid.

Air entrainment

As an example of making history, consider a scalar that records the amount of erosion that occurs at fixed locations along the walls of a die or mold from the impact of liquid metal. Histories of individual fluid particles could include information such as the amount of oxide formation that has occurred when the fluid article is on a liquid metal surface during the filling of a die.

Air entrainment at the surface of turbulent water flow provides still another type of history record in which air is captured, advected and then diffused throughout a mass of water by turbulent mixing. The adjacent plot show how air may be pulled into water flowing over a spillway because of turbulent mixing at its free surface (red indicates the greatest air content).

FLOW-3D has built-in options for some history agents (e.g., surface oxide and lost foam residue defects). However, the creation of special agents using the customizing features available in the program is easy and provides the greatest flexibility for special applications. Why not make a little history yourself by putting your own special software agents to work?