I've never seriously studied Norwegian, much to my dad's chagrin... so if it has a name of its own (i.e. w=doubleyoo), I don't know it.

I *can* give you, however, a vague approximation of the sound that it represents. Stick your lips out like you're going to say "oooo", and say "eeee" through those lips. I recommend trying it alone - if someone sees you practicing it, you'll develop a reputation that you may or may not deserve...