Visualization Panel

It just consists of a slider at the top and a visualization of the simulation domain. With the slider you can adjust the speed of the lid at the top of the domain. The further you draw it to one side, the faster the lid is pulled in that direction. To give you a feedback when the slider is in its center position (i. e. the lid is not moving), the slider turns to a darker grey.
The visualization panel shows by default the speed of the fluid mapped to different colors. See the description of the visualization controls for more details.

Simulation Controls

With the "Start/Pause" button you can start and pause the simulation. A green button signals that the simulation is running right now, red means pausing.
To reset the fluid to its initial state (no movement at all) press the "Reset fluid" button below.
Depending on the performance of your computer you can adjust the size of the simulation grid. The smaller the domain, the faster the simulation (I bet you would have guessed that ;-) ). The entire simulation will be reset when you change the grid size. This also includes the obstacles and the tracers, which will be explained later.

Obstacle Controls

One nice feature of the Lattice-Boltzmann method used here is the fact, that it can deal with complicated and changing obstacle structures. Obstacles means in this case that the fluid cannot flow through obstacles and that the fluid's speed is zero at the surface of obstacles.
To place or erase an obstacle, you have to left-click into the visualization panel. You can also drag the mouse while keeping the mouse button pressed to draw lines of obstacles. The "Set/Erase" button toggles between setting (dark) and erasing (light) obstacles. Another way to toggle the button is to right-click in the visualization panel.
The "Clear" button does exactly what you would expect it to do.
You can also choose from some built-in scenarios if you selected a grid size of 150. Just keep in mind that although you can still modify the scenario, these modifications will not be stored.

Visualization Controls

The most important control in this section is the choice of the color-mapped visualization. There are four options, which all have slightly different color mappings:

Velocity: The velocity has an artificial unit of pixels/iteration.

0.0 0.3
x/y-Velocity: Negative and positive x/y-velocities can easily be distinguished.

-0.3 0.0 +0.3
Density: The dimensionless equilibrium density is 1.0 .

0.5 1.0 1.5

As you can see all four color mappings are wrapped, i. e. a value lower resp. higher than the minimum resp. maximum value is projected again to the color corresponding to the maximum resp. minimum value.

Tracers are just some way to visualize the movement in the fluid. They are virtual particles without mass or momentum that follow the current and do not influence the fluid's behavior in any way. Nevertheless their update consumes some computation power. If you feel the need for some extra speed boost, turn them off using the "Tracers on/off" button. Below you can choose the density of the tracers.
Finally, you can select the number of performed time-steps between the update of the visualization. Increase it to get better computing performance, but be prepared for a jerky visualization display.
The last number in this panel displays the number of Mega Lattice Site Updates per second. It is just meant as a performance indicator and has no impact on the simulation itself. To give you an idea: with an 1.4GHz-Athlon I get about 1.7 MLSUD/s.