Nothing can be more frustrating than having a rack full of nothing but vowels. Granted, it's not nearly as bad as having a rack full of nothing but consonants, but to be successful at crossword games, you need to have a rack that is balanced, usually with the letters R-A-T-E-S as the basis for that balance.
Both Scrabble and Words With Friends have this issue, so to be a competent player, you have to know what to do with a rack that looks like A-A-E-U-U-I-O. You might have some questions. We understand.
When it comes to speaking, there could be as many as 20! Even in writing, there could be more than A-E-I-O-U-Y-W. Archaeology, for example, could treat the ae as a single vowel similar to the ä in German. Generally, for crossword games, A-E-I-O-U are considered vowels, and the other letters are considered consonants.
The words with only A-E-I-O-U that are legal to play are all short vowel words of two or three letters. Examples include aa, ae, and eau. If you include Y, then you can get long vowel words like ayaya. You might read about other long vowel words, like a medieval musical term, euouae, but these are not legal in the Official Scrabble Players' Dictionary.
Almost all vowel words that are legal to play have consonants in them. Some of them are great because they not only get rid of multiple vowels, but they also get rid of troublesome consonants. Vacuums is a bingo, and it cleans a V and two Us out of your rack at once. Oozing, queue, and uvea are great to get you out of a low-scoring rack. Check the vowel words you think up in the Official Scrabble Players' Dictionary, which contains all vowel words. You won't make many Earth-shattering plays like vacuums in your crossword game career, so it would behoove you to focus on short vowel words that quickly restore rack balance when you draw new letters.
If you don't want to do the legwork with the OSPD, there are several word unscramblers that you can use as a Scrabble cheat. You just put the letters in your rack into the tool and click, Enter. The tool unscrambles all of the legal words for you. It's your choice how you want to proceed.