How one can explain the significance of critical velocity along with the free vibration frequencies of fluid conveying pipe?
What performance parameters affect the critical velocity of fluid conveying pipe?
The critical velocity in the pipe flow denotes that once the velocity in the pipe exceeds to this value, the flow becomes turbulent, though while the velocity is below the critical value the flow is laminar. Note that since the velocity in the pipe is not constant, the mean velocity is normally used for this discussion.
Because the turbulent flow is much different from the laminar one, the critical velocity is crucial for the right understanding this flow. However, we must know that every flow has its own critical velocity, for it can be turbulent and laminar depending on the conditions.
The critical velocity in pipe flows is related to the transition from laminar to turbulent flow
Thank you all of you Sir Takeo Nakagawa Lucky Tran Rafik Absi .
However, numerous researchers/academicians discussed and plotted their significant discoveries in terms of the real and imaginary components of fluid conveying pipe frequencies.
In that scenario, what exactly does that real component of complex frequencies represent? Furthermore, at the critical velocity, the real component of complex frequencies is divided into two parts. What will happen in reality at that point?
In addition to the critical velocity, the critical Reynolds number is used to divide the laminar and turbulent flows.
Reynolds number is defined by UL/v, where U the characteristic velocity, L the characteristic length and v the kinematic viscosity of fluid.
I may add to comments of other researchers that transition is not occurring at a specific point but it is a process through which by passing a velocity threshold instability waves appears in the laminar flow and eventually leads to turbulence. The velocity or Reynolds number at which this TS waves occurs is called critical point which is depicted on stability curve for different flow conditions.
The Mohsen’s comment may be sufficient, though the detailed points can be improved.
Because of the limitation of the space and time, I will leave this discussion without adding any other comment.
Critical velocity refers to the flow velocity at which the fluid transitions from laminar to turbulent flow. The parameters affecting the critical velocity are density and viscosity of the fluid, as well as the hydraulic diameter, which for a circular pipe is just the diameter.
These parameters are typically characterized using the dimensionless Reynolds Number, Re = (rho)*V* D/(mu) where rho is density, V is velocity, D is hydraulic diameter, and mu is dynamic viscosity. For a closed pipe, Re < 2300 is generally laminar, and above this number is generally turbulent.
However, the transition zone is not absolute, and flow conditions near the critical velocity may transition sponataneously back and forth between laminar and turbulent flow. Because these flow states are very different in terms of friction, pressure drop, etc., it is not recommended to design systems with flow velocities at or near critical.
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