Description🔗

Base class to set log-law type ground-normal inlet boundary conditions for wind velocity and turbulence quantities for homogeneous, two-dimensional, dry-air, equilibrium and neutral atmospheric boundary layer (ABL) modelling.

The ground-normal profile expressions are due to YGCJ (refer to references below) whereat RH expressions were generalised:

\[u = \frac{u^*}{\kappa} \ln \left( \frac{z - d + z_0}{z_0} \right)\] \[v = w = 0\] \[k = \frac{(u^*)^2}{\sqrt{C_\mu}} \sqrt{C_1 \ln \left( \frac{z - d + z_0}{z_0} \right) + C_2}\] \[\epsilon = \frac{(u^*)^3}{\kappa (z - d + z_0)} \sqrt{C_1 \ln \left( \frac{z - d + z_0}{z_0} \right) + C_2}\] \[\omega = \frac{u^*}{\kappa \sqrt{C_\mu}} \frac{1}{z - d + z_0}\] \[u^* = \frac{u_{ref} \kappa}{\ln\left(\frac{z_{ref} + z_0}{z_0}\right)}\]

where:

References🔗

• The ground-normal profile expressions (tag:RH): Richards, P. J., & Hoxey, R. P. (1993). Appropriate boundary conditions for computational wind engineering models using the k-ε turbulence model. In Computational Wind Engineering 1 (pp. 145-153). DOI:10.1016/B978-0-444-81688-7.50018-8

• Modifications to preserve the profiles downstream (tag:HW): Hargreaves, D. M., & Wright, N. G. (2007). On the use of the k–ε model in commercial CFD software to model the neutral atmospheric boundary layer. Journal of wind engineering and industrial aerodynamics, 95(5), 355-369. DOI:10.1016/j.jweia.2006.08.002

• Expression generalisations to allow height variation for turbulence quantities (tag:YGCJ): Yang, Y., Gu, M., Chen, S., & Jin, X. (2009). New inflow boundary conditions for modelling the neutral equilibrium atmospheric boundary layer in computational wind engineering. J. of Wind Engineering and Industrial Aerodynamics, 97(2), 88-95. DOI:10.1016/j.jweia.2008.12.001

• The generalised ground-normal profile expression for omega (tag:YGJ): Yang, Y., Gu, M., & Jin, X., (2009). New inflow boundary conditions for modelling the neutral equilibrium atmospheric boundary layer in SST k-ω model. In: The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, Taipei, Taiwan.

• Theoretical remarks (tag:E): Emeis, S. (2013). Wind Energy Meteorology: Atmospheric Physics for Wind Power Generation. Springer-Verlag Berlin Heidelberg. DOI:10.1007/978-3-642-30523-8

Usage🔗

The condition requires entries in both the boundary and field files.

Boundary file🔗

<patchName>
{
    type            patch;
    ...
}

Field file🔗

<patchName>
{
    // Mandatory entries
    flowDir         <vector>;
    zDir            <vector>;
    Uref            <scalar>;
    Zref            <scalar>;
    z0              <scalarField>;
    d               <scalarField>;

    // Optional entries
    kappa           <scalar>;
    Cmu             <scalar>;
    initABL         <bool>;
    phi             <word>;
    C1              <scalar>;
    C2              <scalar>;

    // Inherited entries
    ...
}

where:

The inherited entries are elaborated in:

• Function1.H

• PatchFunction1.H

• The RH expressions are special cases of those in YGCJ when C1=0 and C2=1. Both C1 and C2 can be determined by nonlinear fitting of (YGCJ:Eqs. 19-20) with an experimental dataset for k. By default, atmBoundaryLayerInlet boundary conditions compute RH expressions.
• z is the ground-normal height relative to the global minimum height of the inlet patch; therefore, the minimum of z is always zero irrespective of the absolute z-coordinate of the computational patch.
• The derived ABL expressions automatically satisfy the simplified transport equation for k. Yet the same expressions only satisfy the simplified transport equation for epsilon when the model constants sigmaEpsilon is 1.11 with kappa=0.4 (HW:p. 358).
• atmBoundaryLayerInlet boundary conditions inherit inletOutlet traits, so that a given inlet condition can be supplied from all sides of the domain, e.g. a ground-normal cylinder domain having a single inlet/outlet boundary where the changes between inlet and outlet depend on the wind direction and patch normals, so that any change in inflow orientation can be handled with the same mesh.
• d is the displacement height, and “is relevant for flows over forests and cities” (E:p. 28). “The displacement height gives the vertical displacement of the entire flow regime over areas which are densely covered with obstacles such as trees or buildings” (E:p. 28).

Further information🔗

Tutorial:

• N/A

Source code:

• $FOAM_SRC/atmosphericModels/derivedFvPatchFields/atmBoundaryLayer

API:

• Foam::atmBoundaryLayer

History:

• Introduced in version v1806