![]() ![]() From here, the growth (or decay) of these disturbances depends on the nature of the disturbance and the nature of the basic state. These initial conditions are small, often unmeasurable perturbations to the basic state flow. The mechanisms by which these disturbances arise are varied and include freestream sound and/or turbulence interacting with surface curvature, shape discontinuities and surface roughness. The initial stage of the natural transition process is known as the Receptivity phase and consists of the transformation of environmental disturbances – both acoustic (sound) and vortical (turbulence) – into small perturbations within the boundary layer. The level of understanding of each phase varies greatly, from near complete understanding of primary mode growth to a near-complete lack of understanding of bypass mechanisms. Which path is realized physically depends on the initial conditions such as initial disturbance amplitude and surface roughness. Ī boundary layer can transition to turbulence through a number of paths. Improvements in Apparatus for Obtaining Motive Power from Fluids and also for Raising or Forcing Fluids (1875) An experimental investigation of the circumstances which determine whether the motion of water in parallel channels shall be direct or sinuous and of the law of resistance in parallel channels (1883) On the dynamical theory of incompressible viscous fluids and the determination of the criterion (1895) Transition stages in a boundary layer The path from receptivity to laminar-turbulent transition as illustrated by Morkovin, 1994. Examples of titles from his more groundbreaking reports are: His final theoretical model published in the mid-1890s is still the standard mathematical framework used today. Reynolds' publications in fluid dynamics began in the early 1870s. On the other hand, Re = 2000 appears to be about the lowest value obtained at a rough entrance. When extreme care is taken, the transition can even happen with Re as high as 40000. Reynolds found that the transition occurred between Re = 200, depending on the smoothness of the entry conditions. ![]() Reynolds identified the governing parameter for the onset of this effect, which was a dimensionless constant later called the Reynolds number. The point at which this happened was the transition point from laminar to turbulent flow. When the velocity was increased, the layer broke up at a given point and diffused throughout the fluid's cross-section. When the velocity was low, the dyed layer remained distinct through the entire length of the large tube. The larger pipe was glass, so the behaviour of the layer of dyed flow could be observed, and at the end of this pipe was a flow-control valve used to vary the water velocity inside the tube. In 1883 Osborne Reynolds demonstrated the transition to turbulent flow in a classic experiment in which he examined the behaviour of water flow under different flow rates using a small jet of dyed water introduced into the centre of flow in a larger pipe. History Reynolds’ 1883 experiment on fluid dynamics in pipes Reynolds’ 1883 observations of the nature of the flow in his experiments The process applies to any fluid flow, and is most often used in the context of boundary layers. "Transitional flow" can refer to transition in either direction, that is laminar–turbulent transitional or turbulent–laminar transitional flow. Transition is often described as a process proceeding through a series of stages. The main parameter characterizing transition is the Reynolds number. In fluid dynamics, the process of a laminar flow becoming turbulent is known as laminar–turbulent transition. Process of fluid flow becoming turbulent The plume from an ordinary candle transitions from laminar to turbulent flow in this Schlieren photograph. ![]()
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