/Users/<YOURUSER>/Library/Application Support/iPhone Simulator/<IOS-VERSION>/Applications/<APPID>/Documents/<your-file-name>
YOURUSER - Username you are logged in as
IOS-VERSION - The one you are running the app under ex. 6.0
APPID - A unique alphanumeric ID given to your app. Once you delete/clean your app it creates a new one.
your-file-name - The file name that you are looking for.
/Users/mvohra/Library/Application Support/iPhone Simulator/6.0/154FCF8C-B259-4A57-B8BB-E9FD3C1851D1/Documents/evaporation-4.jpg