Bulk Velocity in yt
by trevorfush13＠gmail.com

Hello everyone,
I am analyzing cosmological simulations with yt and I am trying to filter data by the radial velocity of a sphere with a defined center. I set the bulk velocity of the sphere using
v = sphere.quantities.bulk_velocity()
sphere.set_field_parameter('bulk_velocity',v)
However, the numbers that I am having to input in order to filter out the data are extremely large even after setting the bulk velocity. Then I calculated the mean velocity of the sphere:
vx = sphere.mean('velocity_x',weight='density')
vy = sphere.mean('velocity_y',weight='density')
vz = sphere.mean('velocity_z',weight='density')
but even after setting the bulk velocity, the mean velocity of the sphere is not even close to being zero. The exact output is:
The bulk velocity is:
[ -3629508.65339038 -15948968.49831905 6561226.69040721] cm/s
The mean velocity after setting bulk velocity is:
[ -3495226.24285729 -16714324.95702405 5505530.59033089] cm/s
I'm curious if I'm doing something simple wrong or if there is a bigger issue. Any help would be much appreciated!
Thank you!
Trevor Fush