Drilling fluid has three flow regimes which are laminar, transition or turbulent flow. The following illustrations demonstrate three types of flow

In 1883 when Mr Osborne Reynolds did the fluid study, he discovered Reynolds number describing flow of water in a circular pipe. From his experiment, the turbulent flow starts at the Reynolds Number of 2,000 and the complete turbulent flow occurs at the Reynolds Number of 4,000. Therefore, when the calculated Reynolds number of fluid is between 2,000 and 4,000, the transition flow is called.