Globular cluster star density as a function of distance from the center Context: I want to simulate globular clusters in a simple way, just to display the positions of stars. 

Assuming isotropy, what would be a reasonable model of the stellar number density as a function or r, the distance from the center of the cluster?

I'm assuming that such a model would have some free parameters as well.
The usual thing is a King model.

There are indeed free parameters. These are the central density, the "core radius" and a tidal truncation radius.

The background and rationale for these models is given in the link. They provide a pretty good representation of the surface density of globular clusters (or indeed open clusters). They require a numerical scheme to "deproject" from the plane of the sky to 3D.

If you find the nitty-gritty of Abel integrals too tricky in the deprojection, then you could always approximate with a Plummer model. This is analytically and computationally easier to deal with, but lacks a bit of physical realism. Central density and a characteristic radius are free parameters here.