It sounds like you're looking for the PDF of Tone Development Through Interpretation by Marcel Moyse, a classic and highly influential study for flutists (and other wind players).
Here’s the most useful information regarding this article/book:
Moyse was obsessed with the human voice. Many of the studies in the book are actually transcriptions of vocal music (like Gluck’s Orfeo ed Euridice).
Before you put the instrument to your lips, look at the first exercise. Sing the phrase using a neutral syllable (e.g., "Doo" or "Ah").