Documentation of 不+"x" contractions resulting in "r" sounding initial consonant? I've been looking for documentation showing 不+"x" contractions resulting in "r" sounding initial consonants, but to no avail.

This is an interesting phenomenon and I'm sure the regular person would say: "it's just people talking fast, don't over think it," but in technical terms these would be some form of contractions. Think:


不 + 知道 = bu rao
不 + 是 = bu ri


I'm interested to know what kind of research has been done on these contractions, if any.

Any ideas?
This phenomenon is a non-standard regional accent, known as 儿化音. It is a phenomenon in some part of North China, especially in Beijing.


  不知道 (bù zhī dào) → 不儿道 (bùr rào)
  
  不是 (bù shì) → bú shì → 不儿 (búr)
  
  告诉你 (gào sù nǐ) → 告儿你 (gàor nǐ)