Making an object invisible under fluid flow

The invisibility cloak is an artifact that can make the wearer transparent, rendering it undetectable to observers outside. Perhaps, one of the most well-known examples is the invisibility cloak possessed by Harry Potter who used it to great the success in the second wizarding war. For centuries, such a magic device has existed only in science fictions. The recent development of the metamaterial technology provides a possible route to implement the invisibility cloak in reality.