Turning undead works if the level of a cleric surpasses the level of undead. If the difference is large enough, you may see undead literally exploding

You may also experience undead trying to avoid and naturally fleeing your cleric if the difference is not so big. If undead surpasses your cleric you may note they get irritate and attack instead of avoiding.
Anomen initially is low enough. Skeleton warrior is level 9 (rare 10), vampires the same. Anomen rather can call the fire on himself trying to turn such. He may turn ordinary skeleton and lesser shadows this time. The simplest test is to animate dead by himself and then try to turn these.
BTW, note, the cleric should be close enough. At the same time (s)he may turn undead being under protection of Sanctuary spell, so, undead (save but liches) do not see him.
HTH,
L.