Hover over the menu bar to pick a physics animation.

Incompressible Fluid Flow through a Constriction

This will show actual particles flowing from a larger width channel, through a tapered throat and then to a smaller width channel. The initial particle density (particles per unit area) is the same in all three sections of the channel. The flow will be such that the particle density does not change. This behavior corresponds to the flow of an incompressible fluid. To keep the particle density constant, the flow rate in the tapered section has to speed up in the `x` direction as well as adopting a converging speed in the `y` direction. If the starting channel half width is `w_1` and its length is `L_1` and the ending half width is `w_2` and the length of the tapered secion is `L_t` then the speeds in the x and y directions are:

`w=w_1-(w_1-w_2)(x-L_1)/L_t`
`v_x=w/w_1 v_1`
`v_y=-(w_1-w_2)/L_t (y/w) v_x `

where `x` is the particle x coordinate, `y` is the particle y coordinate with respect to the axis of the channel, and `w` is the half width of the channel at coordinate `x`. As you will see, in order to keep the density constant, the spacing between the particle columns increases just enough to compensate for the smaller channel half width at the right. This increase is due to the particles speeding up in the tapered section.