2
Aerodynamic Characterization
of the Surface Layer
Abstract
In this chapter, an assessment was carried out on aerodynamic boundary surface
layer characterization, where vertical vector fluxes of scalar quantities, e.g.,
momentum or sensible heat, are considered constant. This approach is grounded
on the Prandtl mixed layer empirical theory based on the analogy between eddies
in turbulent flow and molecules in laminar flow, allowing for flux-gradient
assumptions. The similitudes between eddy and turbulent diffusivity coefficients
in turbulent and laminar molecular flows were noted here as well as their
differences in meaning. It has been shown that within the surface layer, this
theory is not strictly applicable in very rough canopies such as forests, since
vertical fluxes in these canopies are directed in the opposite direction to the
gradients.
An evaluation of the typical vertical logarithmic profile of the average air velocities
in the surface layer was performed under different conditions of stability. Included
was the empirical treatment of topics such as mass, gradient, Richardson flow
numbers, Monin-Obukhov length, dimensionless stability functions or discrete
equations for vertical moment fluxes, sensitive and latent heat, or gases in direct or
iterative form. This empirical base is instrumental for the assessment of natural and
forced convection and heat transfer in environmental systems.
2.1 General Considerations
Most issues relating to environmental physics such as engineering, excepting
aeronautical matters, occur in the surface layer. Fortunately, the characterization of
turbulence and vertical profiling of mean variables in this layer is straightforward.
The surface or constant flow layer is the lower layer of the atmospheric boundary
layer, corresponding to 10% of the total height, where the vertical heat and mass
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. Rodrigues et al., Fundamental Principles of Environmental Physics,
https://doi.org/10.1007/978-3-030-69025-0_2
13
Aerodynamic Characterization
of the Surface Layer
Abstract
In this chapter, an assessment was carried out on aerodynamic boundary surface
layer characterization, where vertical vector fluxes of scalar quantities, e.g.,
momentum or sensible heat, are considered constant. This approach is grounded
on the Prandtl mixed layer empirical theory based on the analogy between eddies
in turbulent flow and molecules in laminar flow, allowing for flux-gradient
assumptions. The similitudes between eddy and turbulent diffusivity coefficients
in turbulent and laminar molecular flows were noted here as well as their
differences in meaning. It has been shown that within the surface layer, this
theory is not strictly applicable in very rough canopies such as forests, since
vertical fluxes in these canopies are directed in the opposite direction to the
gradients.
An evaluation of the typical vertical logarithmic profile of the average air velocities
in the surface layer was performed under different conditions of stability. Included
was the empirical treatment of topics such as mass, gradient, Richardson flow
numbers, Monin-Obukhov length, dimensionless stability functions or discrete
equations for vertical moment fluxes, sensitive and latent heat, or gases in direct or
iterative form. This empirical base is instrumental for the assessment of natural and
forced convection and heat transfer in environmental systems.
2.1 General Considerations
Most issues relating to environmental physics such as engineering, excepting
aeronautical matters, occur in the surface layer. Fortunately, the characterization of
turbulence and vertical profiling of mean variables in this layer is straightforward.
The surface or constant flow layer is the lower layer of the atmospheric boundary
layer, corresponding to 10% of the total height, where the vertical heat and mass
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. Rodrigues et al., Fundamental Principles of Environmental Physics,
https://doi.org/10.1007/978-3-030-69025-0_2
13