  Observational evidence from local star-forming regions mandates that star
formation occurs shortly after, or even during, molecular cloud formation.
Models of the formation of molecular clouds in large-scale converging flows
have identified the physical mechanisms driving the necessary rapid
fragmentation. They also point to global gravitational collapse driving
supersonic turbulence in molecular clouds. Previous cloud formation models have
focused on turbulence generation, gravitational collapse, magnetic fields, and
feedback. Here, we explore the effect of structure in the flow on the resulting
clouds and the ensuing gravitational collapse. We compare two extreme cases,
one with a collision between two smooth streams, and one with streams
containing small clumps. We find that structured converging flows lead to a
delay of local gravitational collapse ("star formation"). Thus, more gas has
time to accumulate, eventually leading to a strong global collapse, and thus to
a high star formation rate. Uniform converging flows fragment hydrodynamically
early on, leading to the rapid onset of local gravitational collapse and an
overall low sink formation rate.
