The streaming instability ( SI ) has been extensively studied in the linear and non-linear regimes as a mechanism to concentrate solids and trigger planetesimal formation in the midplane of protoplanetary discs .
A related dust settling instability ( DSI ) applies to particles while settling towards the midplane .
The DSI has previously been studied in the linear regime , with predictions that it could trigger particle clumping away from the midplane .
This work presents a range of linear calculations and non-linear simulations , performed with FARGO3D , to assess conditions for DSI growth .
We expand on previous linear analyses by including particle size distributions and performing a detailed study of the amount of background turbulence needed to stabilize the DSI .
When including binned size distributions , the DSI often produces converged growth rates with fewer bins than the standard SI .
With background turbulence , we find that the most favorable conditions for DSI growth are weak turbulence , characterized by \alpha \lesssim 10 ^ { -6 } with intermediate-sized grains that settle from one gas scale-height .
These conditions could arise during a sudden decrease in disc turbulence following an accretion outburst .
Ignoring background turbulence , we performed a parameter survey of local 2D DSI simulations .
Particle clumping was either weak or occurred slower than particles settle .
Clumping was reduced by a factor of two in a comparison 3D simulation .
Overall , our results strongly disfavor the hypothesis that the DSI significantly promotes planetesimal formation .
Non-linear simulations of the DSI with different numerical methods could support or challenge these findings .