  The streaming instability (SI) is one of the most promising candidates for
triggering planetesimal formation by producing dense dust clumps that undergo
gravitational collapse. Understanding how the SI operates in realistic
protoplanetary disks (PPDs) is therefore crucial to assess the efficiency of
planetesimal formation. Modern models of PPDs show that large-scale magnetic
torques or winds can drive laminar gas accretion near the disk midplane. In a
previous study, we identified a new linear dust-gas instability, the azimuthal
drift SI (AdSI), applicable to such accreting disks and is powered by the
relative azimuthal motion between dust and gas that results from the gas being
torqued. In this work, we present the first nonlinear simulations of the AdSI.
We show that it can destabilize an accreting, dusty disk even in the absence of
a global radial pressure gradient, which is unlike the classic SI. We find the
AdSI drives turbulence and the formation of vertically-extended dust filaments
that undergo merging. In dust-rich disks, merged AdSI filaments reach maximum
dust-to-gas ratios exceeding 100. Moreover, we find that even in dust-poor
disks the AdSI can increase local dust densities by two orders of magnitude. We
discuss the possible role of the AdSI in planetesimal formation, especially in
regions of an accreting PPD with vanishing radial pressure gradients.
