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The geometry of the turbulent-nonturbulent interface layer in boundary layers

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The method to obtain the turbulent-nonturbulent interface by defining a threshold for a variable that depends on turbulent fluctuations is revisited. Instead of choosing the threshold from practical considerations, it is considered a parameter. The goal is to find if a particular value for the threshold emerges from the geometrical properties of the resulting surface and the characteristics of the flow at its vicinity.
For this purpose, only methods that are consistent with a three-dimensional fractal-like nature of the surface are applied. A convention for the threshold, that depends only on the geometry of the interface, applicable to different flows, is proposed. However, when this criterion is applied to different scalar fields, or alternative definitions of distance are applied, different results are obtained. This has a direct consequence on any quantity that is obtained from the surface’s geometry, such as normals and thicknesses.

Author(s):

Guillem Borrell    
Universidad Politécnica de Madrid
Spain

Jiménez Javier    
Universidad Politécnica de Madrid
Spain