Question

what is renolds number????

Answer 1

The Reynolds number (Re) is an important dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations. At low Reynolds numbers flow tends to be dominated by laminar (sheet-like) flow, but at high Reynolds numbers turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents). These eddy currents begin to churn the flow, using up energy in the process, and for liquids increasing the chances of cavitation. Reynolds number has wide applications, ranging from liquid flow in a pipe to the passage of air over an aircraft wing. It is used to predict the transition from laminar to turbulent flow, and used in the scaling of similar but different-sized flow situations, such as between an aircraft model in a wind tunnel and the full size version. The predictions of the onset of turbulence and the ability to calculate scaling effects can be used to help predict fluid behaviour on a larger scale, such as in local or global air or water movement and thereby the associated meteorological and climatological effects.

Answer 2

$\huge\textbf{Reynold's Number :}$

It is a pure number which determines the nature of flow of liquid.

If critical velocity of a liquid flowing through a pipe of diameter (d) is given by

$V_{c}$ = $\frac{{N_{R}\:\eta}}{D\:\rho}$

Then,

$N_{R}$ = $\frac{{V_{c}\:D\:\rho}}{\eta}$