openfoam/tutorials/verificationAndValidation/atmosphericModels/atmDownstreamDevelopment

Overview

"By setting appropriate profiles for wind velocity and the turbulence quantities at the inlet, it is often assumed that the boundary layer will be maintained up to the buildings or obstructions in the flow." (HW:p. 355). However, it was quantified by (HW:p. 355) that "even in the absence of obstructions, ..., the velocity and turbulence profiles decay along the fetch" (HW:p. 355). It was shown by (HW:p. 355) that a set of modifications were required to maintain a neutral atmospheric boundary layer throughout an empty and long computational domain of a RANS computation.

Aim

• Verification of the atmospheric boundary-layer boundary conditions in terms of the maintenance of inlet quantities downstream within a RANS computation:
  • atmBoundaryLayerInletVelocity
  • atmBoundaryLayerInletK
  • atmBoundaryLayerInletEpsilon
  • atmBoundaryLayerInletOmega

Benchmark (Physical phenomenon)

• The benchmark is an empty fetch computational domain, steady-state RANS simulation.
• Flow characteristics:
  • External flow
  • The surface layer portion of the neutral-stratified equilibrium atmospheric boundary layer (no Ekman layer)
  • Dry air
  • Homogeneous, smooth terrain
  • Spatiotemporal-invariant aerodynamic roughness length
  • No displacement height
  • Newtonian, single-phase, incompressible, non-reacting
• Benchmark scenario:
  • Computational domain: (HW:Fig. 1)
  • Benchmark dataset: (HW:Fig. 6) (Obtained by the WebPlotDigitizer-4.2 (Rohatgi, 2019))

Resources

Computational study (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

Wind profile (tag:RQP):
    Richards, P. J., Quinn, A. D., & Parker, S. (2002).
    A 6 m cube in an atmospheric boundary layer flow-Part 2.
    Computational solutions. Wind and structures, 5(2_3_4), 177-192.
    DOI:10.12989/was.2002.5.2_3_4.177

Numerics

Physical modelling:

• The governing equations for:
  • Steady-state, Newtonian, single-phase, incompressible fluid flows, excluding any thermal chemical, electromagnetic and scalar interactions
• Mathematical approach for the turbulence modelling:
  • Reynolds-averaged Navier-Stokes simulation (RANS)
• Turbulence closure model:
  • kEpsilon and kOmegaSST linear eddy viscosity closure models
• The sets of input (HW:Table 1):
  • Reference height, Zref = 6 [m]
  • Aerodynamic roughness height, z0 = 0.01 [m]
  • Displacement height, d = 0 [m]
  • Reference mean wind speed, Uref = 10 [m/s]

Computational domain modelling:

• Rectangular prism
• (x1, x2, x3) = (5000, 100, 500) [m] = (streamwise, spanwise, ground-normal) directions

Computational domain discretisation:

• Spatial resolution:
  • (x1, x2, x3) = (500, 5, 50) [cells]
  • Refer to the system/blockMeshDict for the grading details
• Temporal resolution: Steady state

Equation discretisation:

• Spatial derivatives and variables:
  • Convection: Second order
  • Others: Second order with various limiters
• Temporal derivatives and variables: First order

Numerical boundary/initial conditions:

• Refer to 0.orig

Pressure-velocity coupling algorithm:

• SIMPLEC

Linear solvers:

• Refer to system/fvSolution

Initialisation and sampling:

• No initialisation/averaging
• Sampling at the end of the simulation via system/sampleDict
• Refer to system/controlDict for further details