Atmospheric Boundary Layer#

Atmospheric Boundary Layer

1. Project Description#

The objective of this project is to reproduce the properties of atmospheric boundary layer (ABL) through CFD-LES simulations. The wind profiles must reproduce the logaritmic equation from [1].

The reference heights used for velocity normalization was measured at \(H\) = 150 m. One convective time scale is defined as \(CTS = H / U_{H}\).

To achieve different velocity profiles for each terrain category, fins with height \(h\) are distributed across the floor. The fins width was fixed in \(6\) m and the spacing \(x\times y\) in \(16\times32\) m.

After calibration steps, the required height for each category was:

Wind Directions#

Roughness Category

CAT 0

CAT I

CAT II

CAT III

CAT IV

\(\boldsymbol{z_0}\) [m] (roughness height)

0.003

0.01

0.05

0.3

1

\(\boldsymbol{h / z_{0}}\) (fin height to \(\boldsymbol{z_{0}}\) ratio)

0

100

40

13

8

2. Simulation Setup#

The Synthetic Eddy Method (SEM) boundary condition is applied at the inlet of the computational domain. A Neumann boundary condition is applied at the remaining boundaries.

The reference position is at \(1200\) m from the inlet, and 3 grid refinement levels were assessed:

Computational Grid

The simulation parameters were:

Dimensionless Parameters#

\(\boldsymbol{\Delta x / H}\) (spatial res.)

0.0267

0.0133

0.00667

\(\boldsymbol{\Delta t / CTS}\) (temporal res.)

0.0016

0.0008

0.0004

\(\boldsymbol{T / CTS}\) (statistical sample size)

128

128

128

\(\boldsymbol{Re_H = U_{H} H / \nu}\) (temporal res.)

337500

337500

337500

The equivalent parameters in full scale are:

Full-scale Parameters#

\(\boldsymbol{\Delta x}\) [m]

4

2

1

\(\boldsymbol{\Delta t}\) [ms]

8

4

2

\(\boldsymbol{T}\) [s]

640

640

640

The computational resources required were:

Full-scale Parameters#

Device

NVIDIA RTX A5500

NVIDIA RTX A5500

NVIDIA RTX A5500

Refinement

Ref 4 m

Ref 2 m

Ref 1 m

Node count (million)

16.26

28.55

51.85

Allocated memory (Gb)

2.38

4.17

7.62

Ellapsed time (h)

2.13

3.50

7.70

3. Results: Reference Position#

Average Velocity#

Category 0:

CAT 0 - Average velocity profile

Category 1:

CAT I - Average velocity profile

Category 2:

CAT II - Average velocity profile

Category 3:

CAT III - Average velocity profile

Category 4:

CAT IV - Average velocity profile

Turbulence Intensity#

Category 0:

CAT 0 - Average turbulence intensity

Category 1:

CAT I - Average turbulence intensity

Category 2:

CAT II - Average turbulence intensity

Category 3:

CAT III - Average turbulence intensity

Category 4:

CAT IV - Average turbulence intensity

Integral Lenght Scale#

Category 0:

CAT 0 - Integral length scale

Category 1:

CAT I - Integral length scale

Category 2:

CAT II - Integral length scale

Category 3:

CAT III - Integral length scale

Category 4:

CAT IV - Integral length scale

Energy Spectra#

Category 0:

CAT 0 - Average velocity spectra

Category 1:

CAT I - Average velocity spectra

Category 2:

CAT II - Average velocity spectra

Category 3:

CAT III - Average velocity spectra

Category 4:

CAT III - Average velocity spectra

Execution Notes#

Execution Notes#

Execution Date (YYYY-MM-DD)

2025-3-11

Solver Version

1.6.20

Changelog#

Execution Notes

18 April 2024

  • Uploaded point comparisons, simulations executed with Nassu release v1.5.4.