  The bulk flow is a volume average of the peculiar velocities and a useful
probe of the mass distribution on large scales. The gravitational instability
model views the bulk flow as a potential flow that obeys a Maxwellian
Distribution. We use two N-body simulations, the LasDamas Carmen and the
Horizon Run, to calculate the bulk flows of various sized volumes in the
simulation boxes. Once we have the bulk flow velocities as a function of scale,
we investigate the mass and gravitational potential distribution around the
volume. We found that matter densities can be asymmetrical and difficult to
detect in real surveys, however, the gravitational potential and its gradient
may provide better tools to investigate the underlying matter distribution.
This study shows that bulk flows are indeed potential flows and thus provides
information on the flow sources. We also show that bulk flow magnitudes follow
a Maxwellian distribution on scales $>10\ h^{-1}$Mpc.
