Fig. 1: Particle advection behind two obstacles.

Advection is a transport mechanism in which a substance is carried by the flow of a fluid. An example is the transport of sand in a river or pollen in the air. Advection is different from diffusion, whereas the more commonly known term, convection, is the combination of advection and diffusion.

Our Energy2D can simulate advection as it integrates particle dynamics in the Lagrangian frame and fluid dynamics in the Eulerian frame. Particles in Energy2D do not spontaneously diffuse — they are driven by gravity or fluid, though we can introduce Brownian particles in the future by incorporating the Langevin Equation into Energy2D.

Fig. 2: Blowing away particles.

Over this weekend, I added a new object, the particle feeder, for creating continuous particle flow in the presence of open mass boundary. A particle feeder can emit a specified type of particle at a specified frequency. All these settings can be adjusted in its property window, which can be opened by right-clicking on it and selecting the relevant menu.

Figure 1 shows a comparison of particle advection behind a turbulent flow and a streamlined flow. Have you ever seen these kinds of patterns in rivers?

Figure 2 shows how particles of different densities separate when you blow them with a fan. There are six particle feeders at the top that continually drop particles. A fan is placed not far below the feeders.

With these new additions to Energy2D, we hope to be able to simulate more complex atmospheric phenomena (such as pollutant transport through jet streams) in the future.