A NUMERICAL TURBULENCE MODEL FOR MULTIPHASE FLOWS IN THE PROTOPLANETARY NEBULA

It is thought that planets form from solid particles in a flattened, r otating, 99% gaseous nebula. These grains gradually coagulate into mil limeter-to-meter sized aggregates which settle toward the midplane of the nebula. It is widely believed that the resulting dense layer event ually becomes gravitationally unstable and collapses into ''planetesim als.'' A new numerical model is presented to simulate the predominant processes (gravitation, vertical convection, and shear-driven turbulen ce) during the stage while the particulate material is still dispersed about the midplane of the nebula. In our previous work, particles wer e assumed to be spheres of a single radius; in the present work, parti cles are spheres of different radii. Results indicate that neither a b road nor a narrow distribution of particle sizes is likely to become g ravitationally unstable. (C) 1995 American Institute of Physics.