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In fluid dynamics, the Reynolds number (Re) is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. [2] At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers, flows tend to be turbulent.
The equation can either be used with consistent units or nondimensionalized. The Reynolds Equation assumes: The fluid is Newtonian. Fluid viscous forces dominate over fluid inertia forces. This is the principle of the Reynolds number. Fluid body forces are negligible.
The Reynolds and Womersley Numbers are also used to calculate the thicknesses of the boundary layers that can form from the fluid flow’s viscous effects. The Reynolds number is used to calculate the convective inertial boundary layer thickness that can form, and the Womersley number is used to calculate the transient inertial boundary thickness that can form.
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
The Reynolds number is useful because it can provide cut off points for when flow is stable or unstable, namely the Critical Reynolds number . As it increases, the amplitude of a disturbance which could then lead to instability gets smaller. [1] At high Reynolds numbers it is agreed that fluid flows will be unstable.
For low Reynolds number flows, tunnels can use oil instead of water. The advantage is that the increased viscosity will allow the flow to be a higher speed (and thus easier to maintain in a stable manner) for a lower Reynolds number. Often, a tunnel will be co-located with other experimental facilities such as a wave flume at a Ship model basin.
The Reynolds-averaged Navier–Stokes equations (RANS equations) are time-averaged [a] equations of motion for fluid flow. The idea behind the equations is Reynolds decomposition, whereby an instantaneous quantity is decomposed into its time-averaged and fluctuating quantities, an idea first proposed by Osborne Reynolds. [1] The RANS equations ...
This can occur around cylinders and spheres, for any fluid, cylinder size and fluid speed, provided that the flow has a Reynolds number in the range ~40 to ~1000. [ 1 ] In fluid dynamics , an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. [ 2 ]