I just want to share this info about a guy I found on the Internet, his name is Daryl Anton, he is a Cuban professional Flute player and teacher, and has some online classes on YouTube. I find his material very accesible, easy to understand, and over all SUPER well structured and well explained. Maybe you will enjoy him also as much as I am. He has 2 subtitled videos, for English speakers, and his other videos are in Spanish, but yet we can realize what he´s talking about. His last videos are subtitled, so, hopefully he will continue on doing this in 2 languages.
Take a look at his latest video, about the Double Tonguing Technique ! I tried this, and could finally really understand how it works, and the best way ti practice this technique for the Flute.
Here the YouTube Video: https://www.youtube.com/watch?v=xKgMuXOTgJE