In most cases the pronunciation of u as /ju:/ is an indication that the word is connected with a French word. French u is regulary pronounced as /y/ as in
- French le duc /dyk/ - English duke /dju:/, AmE /du:k/
- F dû/due /dy/ - E due /dju:/
- F la vue /vy/ - E view /vju:/
Also German words with ü become words with /ju:/ in English
- G München - E Munich /'mju:nik/
The letter u has the pronunciation (PN) /ʌ/ as in to cut,
and the PN /ju:/ in open syllables as in cu-te. An open syllable has the
structure vowel (no consonant); here only the written form is relevant, not the spoken form. A closed syllable has the structure vowel+ consonant.
In American English /ju:/ is reduced to /u:/ after a certain group of consonants as in
In his comment below Peter Shor has enumerated the special consonants after which /ju:/ is reduced to /u:/.