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In fluid dynamics, a Tollmien–Schlichting wave (often abbreviated T-S wave) is a streamwise instability which arises in a viscous boundary layer. It is one of the more common methods by which a laminar boundary layer transitions to turbulence. The waves are initiated when some disturbance (sound, for example) interacts with leading edge roughness in a process known as receptivity. These waves are slowly amplified as they move downstream until they may eventually grow large enough that nonlinearities take over and the flow transitions to turbulence. These waves, originally discovered by Ludwig Prandtl, were further studied by two of his former students, Walter Tollmien and Hermann Schlichting for whom the phenomenon is named. == Physical Mechanism == In order for a boundary layer to be absolutely unstable (have an inviscid instability), it must satisfy Rayleigh's criterion; namely Where represents the y-derivative and is the free stream velocity profile. In other words, the velocity profile must have an inflection point to be unstable. It is clear that in a typical boundary layer with a zero pressure gradient, the flow will be unconditionally stable; however, we know from experience this is not the case and the flow does transition. It is clear, then, that viscosity must be an important factor in the instability. It can be shown using energy methods that The rightmost term is a viscous dissipation term and is stabilizing. The left term, however, is the Reynolds stress term and is the primary production method for instability growth. In an inviscid flow, the and terms are orthogonal, so the term is zero, as one would expect. However, with the addition of viscosity, the two components are no longer orthogonal and the term becomes nonzero. In this regard, viscosity is destabilizing and is the reason for the formation of T-S waves. 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「Tollmien–Schlichting wave」の詳細全文を読む スポンサード リンク
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