TollmienSchlichtingbølger

The Tollmien-Schlichting wave is a fundamental concept in fluid dynamics, describing a type of instability that can occur in laminar boundary layers. Specifically, it refers to the growth of two-dimensional, small-amplitude, wavy disturbances within a flow that would otherwise be smooth and predictable. These waves arise when the flow's inertia overcomes the viscous forces that tend to dampen disturbances. The existence and behavior of Tollmien-Schlichting waves were first theoretically predicted by Hermann Tollmien and later experimentally confirmed by Werner Schlichting.

The onset of Tollmien-Schlichting waves is governed by the Reynolds number, a dimensionless quantity that represents the ratio of inertial forces to viscous forces. Below a certain critical Reynolds number, any disturbances in the flow will decay. However, as the Reynolds number increases and surpasses this critical value, these disturbances begin to grow, propagating downstream as Tollmien-Schlichting waves. The wavelength and growth rate of these waves are dependent on the specific flow conditions, including the shape of the surface and the freestream velocity.

The development of Tollmien-Schlichting waves is a crucial step in the transition from laminar to turbulent flow. While the waves themselves are still considered a laminar phenomenon, their growth can lead to significant three-dimensional disturbances. These three-dimensional disturbances can then further amplify, leading to the breakdown of the orderly laminar flow into the chaotic and unpredictable nature of turbulence. Understanding Tollmien-Schlichting waves is therefore essential for predicting where and how this transition will occur, which has significant implications in fields like aerodynamics, where it affects drag and lift.