With reference to a post on page 2, in German the letter Y did not originally exist in any native word but has crept in via adopted foreign words and, from by default being a consonant because the list of vowels did not contain it, it is now regarded as a German vowel because it is almost always pronounced as such (English influence being an exception).
Don't want to spoil this, but a vowel represents a sound which can be made without a consonant. To this extent both y and w are classed as semi-vowels. If you want a list of words without a,e,i,o,u, then a Welsh dictionary is the best place to start (although all the word have vowel sounds).