Definition - What does Turbulent Flow mean?
Turbulent flow can be defined as a type of flow in which the drilling fluid undergoes irregular fluctuations instead of a smooth laminar flow. The velocity of the fluid is undergoing continuous changes in both magnitude and direction. The flow turns from streamlined to turbulent when the fluid reaches critical velocity.
Critical velocity can be calculated using Reynolds number which characterizes the flow as streamlined or turbulent.
Trenchlesspedia explains Turbulent Flow
Drilling fluid has three flow regimes namely plug flow, laminar flow, and turbulent flow. In between these zones are transition zones where the flow regimes change. At very low shear rate when the mud is in the gel stage, the flow can be classified as plug flow, where the velocity of the mud at the center of the annulus is equal to the velocity of the mud at the sides. In laminar flow, the shear rate is a function of the shear stress of the fluid and the flow has a predictable pattern.
In the turbulent flow, the flow is disorderly and difficult to describe since it is subject to random local fluctuations. Reynolds number above 4000 indicates a turbulent flow meaning the flow velocity is critical. When calculating critical velocity, Reynolds number plays an important role.