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Monin Obukhov Neutral

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Scope

The benchmark is open to participants of the Wakebench project using surface layer models. This is the first element of the building-block approach so it should be mandatory if you intend to participate in other test cases down the line.

The benchmark consists on empty domain (flat terrain) simulations of the neutral surface boundary layer in steady-state conditions. 

Objectives

Demonstrate that the flow model, when run in M-O conditions, is able to reproduce the analytical expressions of the profiles predicted by the theory for neutral conditions. At the same time, it will be possible to check the compatibility of the wall treatment with the flow model for a range of surface roughness conditions.

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench. In the future it will be open for public access.

Input data

The conditions for simulating the M-O profiles in neutral conditions are:

  • von karman constant: κ = 0.4

  • Roughness length: z0 = [0.0002, 0.03, 0.4] m

  • Obukhov length: L = ∞

  • Use dry air with a density ρ = 1.225 kg/m3 and dynamic viscosity μ = 1.73e-5 kg/ms

Validation data

The validation data will consist on normalized M-O profiles obtained from analytical functions.

Model runs

An empty domain of 3x0.5x0.5 km (x,y,z) dimensions should be simulated with three different values of roughness length in the ground wall.

  • Run 1: z0 = 0.0002 m, typical of offshore conditions

  • Run 2: z0 = 0.03 m, typical of open fields with low vegetation

  • Run 3: z0 = 0.4 m, typical of forested terrain

The origin of the coordinate system will be placed in the middle of the bottom edge of the inlet wall. The modeler is free to configure the computational grid according to own criteria. 

Output data

Please provide output vertical profiles of mean velocity (U) and turbulent kinetic energy (tke) at the outlet (x = 3000 m, y = 0) using the file naming and format convention described in the Windbench user's guide with profID = outlet# (# is the run number = [1,2,3]). Mention the friction velocity (u*) used in the study since this input will be used to normalize the results.

Remarks

When analyzing deviations from the M-O profiles, it is important to have a good description of the wall treatment in the evaluation questionnaire. Please specify which wall functions and boundary conditions are used and how you build your grid to account for the varying roughness length. 

Terms andConditions

Not applicable