CFD investigation of the atmospheric boundary layer under different thermal stability conditions

Pieterse, J.E.; Harms, Thomas

doi:10.1016/j.jweia.2013.07.014

Cited by 56 publications

(29 citation statements)

References 41 publications

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“…Generally, all profiles show zero gradient at the horizontal boundaries. For both actual and idealised models, the ground and building walls were assigned a no-slip condition and wall functions were used to calculate the turbulent kinetic energy at the wall nearest to the grid point [31,32]. The surface roughness height (z0) was taken as 0.1×11 m in AM and 0.1×11 mm in WTM [33].…”

Section: Boundary Conditionsmentioning

confidence: 99%

Large eddy simulation of wind flow through an urban environment in its full-scale wind tunnel models

Reda

Zulkifli²,

Harun³

2017

J. MECH. ENG. SCI.

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Wind flow through urban areas is studied either by wind tunnel scale experiments or via computational fluid dynamics simulations through full-scale actual models. The large difference between the Reynolds numbers based on the geometries of actual cities and wind tunnel scale cities makes the dynamic similarity between the two models uncertain. In this study, the mean and turbulent flow parameters were investigated using a large eddy simulation for two models i.e. the actual urban area model and the wind tunnel scale (1:1000) model. Kuala Lumpur City Centre, Malaysia, was considered as the case study of an urban area. Vertical velocity profiles were plotted at five locations representing different building packing densities. The results of wind tunnel scale model largely agreed with the actual model with some discrepancies in the building vicinity and wakes. The dissimilarity of the wake patterns due to the large difference in Re was responsible for the deviations. Largest discrepancies were found in the lateral and wall-normal velocity components and turbulence stresses. The results casted a shadow on the applicability of the conclusions derived from the simulations on wind tunnel scale models to the actual urban environments they represented. The deviation between the two models should be assessed before proceeding with experimental or numerical simulations on small-sized models.

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Section: Boundary Conditionsmentioning

confidence: 99%

Large eddy simulation of wind flow through an urban environment in its full-scale wind tunnel models

Reda

Zulkifli²,

Harun³

2017

J. MECH. ENG. SCI.

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“…The lateral boundaries were assigned periodic conditions as well [9,12,26,29]. For both actual and idealised models, the ground and building walls were assigned a no-slip condition and wall functions were used to calculate the turbulent kinetic energy at the wall nearest grid point [30,31]. The surface roughness height (z0) was taken as 0.1×11 m in all models [32].…”

Section: Boundary Conditionsmentioning

confidence: 99%

Towards developing an idealised city model with realistic aerodynamic features

Reda

Zulkifli²,

Harun³

2017

J. MECH. ENG. SCI.

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Many concerns related to natural ventilation in urban areas have been deduced from experimental or computational fluid dynamics simulations on idealised models. However, it is not definite that the flow through these idealised models presents similar characteristics to actual urban areas. The objective of this research is to suggest an approach to close the gap between idealised models and genuine cities; i.e., predict actual urban flow characteristics from the ready data of idealised models. The flow was simulated by large-eddy simulation through both the actual city model and a group of idealised models of different structures but the same average dimensions and buildingpacking-density as the actual city. The numerical setup was validated by comparison with wind tunnel measurements from the literature. It was found that an equivalent to the average velocity profile throughout an idealised model can be achieved by a mix of the "five-point spatial average" and the "four-point spatial average". The vertical profiles of mean and turbulent windward velocities of the idealised models manifest a general similarity to those of the actual model. On the other hand, the cross-wind and wall-normal components show large discrepancies. In all cases, the idealised models exhibit very narrow atmospheric surface layer heights compared to the actual model. IM-RAN (which represents a structure of semi-random configuration) displayed the closest results to the actual model but condensed in half the actual model surface layer height. A correction formula was devised to close the gap between the two models. The results confirm the ability to utilise idealised models to deliver recommendations regarding urban environment planning; though, attention should be paid to the selection of the idealised model and corrections may be needed.

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“…CFD codes employing RANS turbulence generally model the flow under turbulent conditions near walls using a wall function, providing that the flow velocity (constant) at the inlet is chosen to be the mean wind velocity of the wind profile [16]. The roughness of these surfaces is often expressed in terms of the equivalent wall roughness height k s [18,19].…”

Section: Using the Wall Function With A Uniform (Constant)mentioning

confidence: 99%

“…These discrepancies could be reported as inaccuracies in the boundary conditions for the flow or the pollutant source and the underestimation of the turbulence kinetic energy [14,15]. The standard k-ε turbulence model, widely employed in the simulation of the ABL due to the availability of appropriate boundary conditions and meteorological data [16][17][18][19][20][21], will serve as the starting point in investigating of the ABL under the influence of surface heat flux. The re-normalization group (RNG) k-ε model which renormalizes the Navier-Stokes equations to account for small-scale turbulence [22].…”

Section: Introductionmentioning

confidence: 99%

CFD Modeling of the Atmospheric Boundary Layer in Short Test Section Wind Tunnel

Yassen¹

2015

AJAE

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Abstract:The aim of this paper is to provide a contribution to algorithms for the numerical simulation of the atmospheric boundary layer (ABL) in short test section wind tunnel, with the lowest pressure loss possible, for large Re, similar to the high values observed in nature. Different turbulent models have been examined for their relative suitability for the atmospheric boundary layer airflow with and without the implementation of buoyancy effects with modified turbulence model constants for the atmosphere. Validation of turbulent models through comparison with wind tunnel experiments is essential for practical applications. It has been observed that the k-ε model is most suitable tool for generation of an ABL in short-chamber wind tunnel. A comparison has been made with the available experimental data, from literature, and the predicted CFD values are very close to the corresponding experimental measurements. The simulation results show the importance of turbulence model constant (C µ ), the non-uniform velocity and turbulence intensity profiles. Also, the significance of y + for consistent assessment is confirmed. However, it has been found that the buoyancy force makes significant change in boundary layer thickness without a major impact on computation time.

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CFD investigation of the atmospheric boundary layer under different thermal stability conditions

Cited by 56 publications

References 41 publications

Large eddy simulation of wind flow through an urban environment in its full-scale wind tunnel models

Large eddy simulation of wind flow through an urban environment in its full-scale wind tunnel models

Towards developing an idealised city model with realistic aerodynamic features

CFD Modeling of the Atmospheric Boundary Layer in Short Test Section Wind Tunnel

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