  Aims: We aim to determine the effect of converging flows on the evolution of
a bipolar magnetic region (BMR), and to investigate the role of these inflows
in the generation of poloidal flux. We also discuss whether the flux dispersal
due to turbulent flows can be described as a diffusion process.
  Methods: We developed a simple surface flux transport model based on
point-like magnetic concentrations. We tracked the tilt angle, the magnetic
flux and the axial dipole moment of a BMR in simulations with and without
inflows and compared the results. To test the diffusion approximation,
simulations of random walk dispersal of magnetic features were compared against
the predictions of the diffusion treatment.
  Results: We confirm the validity of the diffusion approximation to describe
flux dispersal on large scales. We find that the inflows enhance flux
cancellation, but at the same time affect the latitudinal separation of the
polarities of the bipolar region. In most cases the latitudinal separation is
limited by the inflows, resulting in a reduction of the axial dipole moment of
the BMR. However, when the initial tilt angle of the BMR is small, the inflows
produce an increase in latitudinal separation that leads to an increase in the
axial dipole moment in spite of the enhanced flux destruction. This can give
rise to a tilt of the BMR even when the BMR was originally aligned parallel to
the equator.
