Coherent eddies and turbulence in vegetation canopies the mixing layer analogy
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Coherent Eddies and Turbulence in Vegetation Canopies: The mixing-layer analogy. M.R.Raupach, J.J.Finnigan and Y.Brunet Boundary-Layer Meteorology 78: 351-382, 1996. Objectives.

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Coherent Eddies and Turbulence in Vegetation Canopies: The mixing-layer analogy

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Coherent eddies and turbulence in vegetation canopies the mixing layer analogy

Coherent Eddies and Turbulence in Vegetation Canopies: The mixing-layer analogy

M.R.Raupach, J.J.Finnigan and Y.Brunet

Boundary-Layer Meteorology 78: 351-382, 1996


Objectives

Objectives

  • This paper argues that the turbulence near the top of the canopy is similar to that of a plane mixing layer rather than of the boundary layer


The mixing layer

The Mixing Layer

  • The mixing layer is the turbulence shear flow formed between two coflowing streams with different velocities.

  • The characteristic of the mixing layer is a strong inflection in the mean velocity profile.

  • Mixing layer turbulence has a distinctive pattern of coherent motion. It has streamwise periodicity, which is proportional to the vorticity thickness. The ratio ranges 3.5 to 5.

  • Turbulence depends on depth and friction velocity and is sensitive to initial conditions.


The mixing layer1

The Mixing Layer


The canopy

The Canopy


The conopy

The Conopy


The canopy1

Eddies dominating turbulence transfer are of canopy scale.

Three types of observations:

Honami waves

Two-point turbulence statistics

Conditional analyses

The Canopy


The mixing layer analogy

The Mixing-Layer Analogy


The mixing layer anology

The Mixing-Layer Anology


Conclusions

Conclusions

  • Introduced basic properties of turbulence in canopies and in the mixing layer

  • Validated the mixing-layer analogy for the canopy by tests in three aspects: statistical flow properties, the turbulence energy budget and turbulent length scales

  • Described several useful statistical and observational methods in turbulence study


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