What chord is this?

First, name the notes:

D-Bb-Eb-F

Try to arrange them in sequence so there's some kind of third between each of the first three notes:

Bb-D-F-Eb

Name them in relation to the lowest note:

1-3-5-4 (all notes are in the key of Bb)

The 1-3-5 tells you it's a major chord. The 4 is the same as the 11, so its:

Bb(add11)

Thanks. :)