My model is set up as a pipe with an inlet and an outlet. I wish to insert individual particles randomly on the surface of the inlet to investigate the dispersion of them with various changes in the fluid flow. My mesh around the inlet will not be linear across it and therefore if I use the "surface" injection function I will have a majority of the particles released in a certain area.

Is it possible to write a user-defined function to enable the random injection of particles of the same physical properties (and how would I go about doing this?).

The additional problem is that the diameter of the particles I am releasing would be roughly 5% of the pipe diameter, and therefore could not be released all at once, but would have to be done individually.

Any ideas how I might go about this would be very helpful!

Hi Iain, I never did something with user-defined function but I can tell you how to create a plane with a linear distribution of injection points. Create a plane (menu surface). Select the options bounded and Sample Points. Then you can define how many points you want for injection (sample density).

Wolfgang