To clarify a few things (since I'm under the impression you're new to this):
Adults in han culture had secondary names generally called style names. Some people like to refer to their favorite Three Kingdoms figures by style names as a sign of respect or fondness; so they call Zhuge Liang by his style Kongming; Lu Bu by his style Fengxian; Zhao Yun is Zilong, etc. It's particularly common with figures who became famous through the
Romance or other fictionalized works.
Sun Fin wrote:The V thing is about different Chinese characters. In Pingyuan (Chinese written in Western script) just within the Three Kingdom period we have Lu Bu, Lu Meng, Lu Xun and Lu Fan for example. In the original language lot's of those 'Lu's' have different symbols meaning they are all from different clans. Lu Bu should be written LÜ Bu. However as most Western computers can't type Ü some people write is as V instead to make it clear they're not all related.
Again, for the purpose of clarification:
Chinese can be written in two ways; characters (Hanzi) or Pinyin (we'll avoid other systems of Romanization for now). Pinyin is an attempt to put the phonetic sounds of the characters into a form Western readers can understand. It's the way you usually see names written. Without getting into the details of how it all works, let's just say that Pinyin is much less precise than Hanzi.
For example, the characters for Lu Su's name are 魯肅. The characters for Lu Xun's name are 陸遜. In Hanzi, it's clear that these are two totally different Lu-s. 魯 and 陸 are different characters with different meanings. This isn't always clear in Pinyin, especially when tonal marks are not included.
The characters for Lü Bu's name are 呂布. In Pinyin, there are basically two different U-s. The u in Lu Su and the ü in Lü Bu make distinctly different sounds when pronounced correctly. They're as different as, say u and o or a and e. 呂 makes the ü sound while 魯 and 陸 make the standard u noise.
To differentiate these sounds, formal Pinyin adds the diaeresis (those two dots). But this isn't standard on most keyboards. So in the interest of convenience, it is generally acceptable to substitute the letter v instead of ü. The letter v is not used anywhere in the Pinyin alphabet, and it has a similar shape to ü, so this makes the distinction clear.
As for the name Bu (布): it wasn't a very common name, but it wasn't unique to Lü Bu. It was also the name of Wu's Sun Bu (孫布) and Jin's Wang Bu (王布). It was also used in the style name (Zibu 子布) of Wu's great minister Zhang Zhao (張昭).