This tool lets you simulate Knudsen Thermal force (a force caused by a temperature gradient), and was designed to simulate a real experiment. The basic setup of this simulation is a rectangular simulation domain with one or two squares. You can choose the dimensions of the simulation domain, the boundary conditions (characteristics of each boundary of this simulation), dimensions and collision characteristics of the surface(s), and simulation parameters.
The first four inputs on this page ask you for the simulation domain dimensions. The first two ask you for the lower x and y coordinates, which are the coordinates of the lower left hand corner. The next two inputs ask you for the coordinates of the upper right hand corner. For example, if I typed in 0 for the lower x and y coordinates, and 1 for the higher x and y coordinates, the four corners of the simulation domain would be (0,0), (0,1), (1,1), and (1,0).
The last two inputs ask you for the number of grids in the x and y direction. DSMC splits up the simulation domain into grids. The more grids you have, the more accurate the simulation will be, but more grids means the simulation takes longer.
The first four inputs ask you for the boundary conditions of the x and y boundaries. You can choose the following choices: r (specular reflection), o (outflow), p (periodic), and s (surface). You can see more information about this by hovering your mouse over these inputs. Note that if you choose the option 'p' for any of the boundaries, you will not be able to input anything into the opposite boundary because 'p' applies to both boundaries. For example, if you choose the option 'p' for the lower x boundary, you won't be able to input anything in for the higher x boundary as 'p' will apply to both of the boundaries.
If you choose 's' for any of the boundaries, a few more options will appear below. These options will let you define the collision characteristics of the surface. The first option asks you if you want a specular or diffuse collision. If you select 'no' (which is specular collision), you are done inputting the collision characteristics of this boundary. By selecting 'yes' (which is diffuse collision), you will need to input the temperature of the surface, and the accommodation coefficient. This is the option you need if you want for the boundary to have a different temperature than the gas.
This page let's you define the location and size of the rectangular surface(s), as well as their collision characteristics. Defining the size and location of the surface is the same as what you did for the simulation domain. The collision charactersitics are the same as defining those for boundary collisions. One button let's you add a second square to the simulation. Make sure the squares do not overlap, and are inside the simulation domain, or else this GUI will crash.
This page contains all of the characteristics of the gas and flow. The Number Density is the number of molecules in a cubic meter. The next option is described by it's name: number of simulated particles within each grid cell. DSMC creates computational, or simulated, particles that represent real flow. Usually, you want there to be about 10-20 simulated particles for each grid cell. Using this parameter, the GUI will find a number called fnum.
Fnum is the number of real particles that each simulated particle represents, which means fnum equals the number of real particles in the simulation domain divided by the number of simulated particles. The number of real particles is equal to the number density multiplied by the area of the domain (in meters). The number of simulated particles is equal to the number of particles in each cell multiplied by the number of grid cells. Note that fnum can be on the order of 10^10 more depending on exactly what each case needs.
The next few inputs are self explanatory. Choose the gas mixture, choose the average velocity of the gas in the x and y directions (note that each individual molecule can still have a different velocity, this is just the average of the entire cell). Choose the temperature of the gas, the size of the timestep (the smaller the timestep, the more accurate the simulation is, but the longer it will take.
Next, you input the number of timesteps that this simulation will run.
The next input asks you whether or not you want there to be an external flow into the simulation. By selecting yes, you will allow for there to be a flow from the direction of one or more of the boundaries. You can select which boundaries you want for there to be an inflow. Please note that if you selected a periodic boundary condition, you will not be able to have any inflow from those two boundaries. If you do, this GUI will ignore the inflow command.
The next input let's you create particles in the simulation before the first timestep. If you keep this number at zero, the simulation will start as a vacuum. If you keep this number at zero, and do not add any flow, there will be no particles in the simulation.
The last two inputs are the names of your output files. This will let you run several cases and not overwrite your past output files if you change the name of the file.