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The process of a laminar flow becoming turbulent is known as laminar-turbulent transition. This is an extraordinarily complicated process which at present is not fully understood. However, as the result of many decades of intensive research, certain features have become gradually clear, and it is known that the process proceeds through a series of stages. "Transitional flow" can refer to transition in either direction, that is laminar-turbulent transitional or turbulent-laminar transitional flow. While the process applies to any fluid flow, it is most often used in the context of boundary layers due to their ubiquity in real fluid flows and their importance in many fluid-dynamic processes. ==History== Osborne Reynolds demonstrated the transition to turbulent flow in a classic experiment in which he examined an outlet from a large water tank through a small tube. At the end of the tank there was a stopcock used to vary the water speed inside the tube. The junction of the tube with the tank was nicely rounded. A filament of colored fluid was introduced at the mouth. When the water was slow, the filament remained distinct through the entire length of the tube. When the speed was increased, the filament broke up at a given point and diffused throughout the cross-section. Reynolds identified the governing parameter, the dimensionless Reynolds number. The point at which the color diffuses throughout the tube is the transition point from laminar to turbulent. Reynolds found that the transition occurred between ''Re = 2000'' and ''13000'', depending on the smoothness of the entry conditions. When extreme care is taken, the transition can even happen with ''Re'' as high as ''40000''. On the other hand, ''Re = 2000'' appears to be about the lowest value obtained at a rough entrance. Reynolds' publications in fluid dynamics began in the early 1870s. His final theoretical model published in the mid-1890s is still the standard mathematical framework used today. Examples of titles from his more groundbreaking reports: :''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) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Laminar-turbulent transition」の詳細全文を読む スポンサード リンク
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