I recently learned the word 運輸{うんゆ}, which has ん immediately followed by ゆ. However, seeing this made me wonder in what way this is different to にゅ. I can't imagine that there's much of a difference in pronunciation because both have n immediately followed by y, so I thought this might be similar to how double consonants use ん instead of っ.
Is there a difference between んや、んよ、んゆ and にゃ、にょ、にゅ, or is it simply a difference in how they're written?
There is a difference in pronunciation. Between vowels (and at the end of words), the moraic nasal (ん) becomes a nasalized echo of the preceding vowel. The contrast can be seen when transcribed into the IPA in the following (I have placed the period between mora rather than syllables for the sake of demonstrating the difference in the length of the words too):
うにゅ isn't a word though. For an example of real (if uncommon) words, here's one pair:
While nasal vowels are fairly common across languages, English doesn't feature them on a phonemic level, so it might take some practice to learn how to pronounce them.
ん is not really n. We romanize it as so, but it's really ŋ.
Actually, you can already pronounce it. Start by saying "sing." Then, say it without the g. But not as seen. Finish in the position of saying g, but don't say g. In contrast, try saying "seen guh." You can also find this sound in ankle and a few other words.
So, にゃ is exactly as you think and one syllable. But んや is two syllables ŋ+ya. But really, うんゆ is two syllables うん+ゆ.
Hope this clarifies everything.
