SIMULATIONS OF ATMOSPHERIC FLOW OVER COMPLEX TERRAIN (original) (raw)
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INTRODUCTION The study of the flow at the atmospheric boundary layer has been intense over the last years. A more comprehensive understanding of the complex phenomena involved in this particular type of flow is being sought, aiming the analysis of structural implications due to strong winds (neutral atmosphere), the pollutant dispersion under neutral or stable conditions and also for meteorological purposes. The phenomenal increase in computer power over the last two decades has led to the possibility of computing such flows by the integration of the (modelled, time-averaged) Navier-Stokes equations. Raithby et al [1] employed the k-ε model (with modification in the C µ value) to calculate the neutrally buoyant flow over the Askervein hill, and compared their numerical results with the experiment made over the real terrain in Scotland. Dawson et al [2] also used the k-ε model (with some modification in the constants of the dissipation equation) to simulate the flow and dispersion over Steptoe Butte (Washington, USA) under neutrally and stably stratified atmosphere. Their results were favorably compared with experimental data, indicating that mathematical models using the eddy viscosity assumption in the turbulence closure could be used to predict the flow and pollutant dispersion over complex terrain. Koo [3] developed a non-isotropic modified k-ε to account for different eddy diffusivities in the lateral and vertical directions in the atmosphere. His model is derived from the algebraic stress model and was applied in one-dimensional problems to predict the vertical profiles of velocity, potential temperature and turbulence variables for horizontal flow in a homogeneous boundary layer. Also, the model was applied in two-dimensional problems to simulate the sea breeze circulation and the manipulation of the atmospheric boundary layer by a thermal fence. Koo's model is similar to the level 2.5 model of Mellor and Yamada [4]. Recently, Castro and Apsley [5] compared numerical (using a " dissipation modification " k-ε model, as named by the authors) and laboratory data for two-dimensional flow and dispersion over topography. In the present work we extend the application of Koo's modified k-ε model to predict three-dimensional neutrally stratified flows over complex terrain. Our final
Flow over Hills: A Large-Eddy Simulation of the Bolund Case
Simulation of local atmospheric flows around complex topography is important for several applications in wind energy (short-term wind forecasting and turbine siting and control), local weather prediction in mountainous regions and avalanche risk assessment. However, atmospheric simulation around steep mountain topography remains challenging, and a number of different approaches are used to represent such topography in numerical models. The immersed boundary method (IBM) is particularly well-suited for efficient and numerically stable simulation of flow around steep terrain. It uses a homogenous grid and permits a fast meshing of the topography. Here, we use the IBM in conjunction with a largeeddy simulation (LES) and test it against two unique datasets. In the first comparison, the LES is used to reproduce experimental results from a wind-tunnel study of a smooth threedimensional hill. In the second comparison, we simulate the wind field around the Bolund Hill, Denmark, and make direct comparisons with field measurements. Both cases show good agreement between the simulation results and the experimental data, with the largest disagreement observed near the surface. The source of error is investigated by performing additional simulations with a variety of spatial resolutions and surface roughness properties.
Numerical Model Validation of Atmospheric Boundary Layer Over Complex Terrain
2005
A numerical model is proposed in this paper to simulate the atmospheric boundary layer (ABL). The results obtained by the numerical model were validated using experimental data presented in the literature. The governing equations of the geophysical flows are the continuity, momentum and energy conservation equations. The momentum equations are coupled to the energy equation by an equation of state. Turbulence is considered in the model using k-ε model. The irregularities of the terrain due to the vegetation are treated as an average rugosity. The computational domain is defined as an area far enough the interest region in order to guarantee the development of the wind flow from the inflow boundary edges. The top boundary of the domain is prescribed at least 500 m above the atmospheric boundary layer. At this altitude the wind flow is considered stable enough so that the Newman boundary condition can be applied. The terrain boundary has a major contribution on the flow structure than...
Numerical Simulation of Topographic Effects on Wind Flow Fields Over Complex Terrain
Proceedings of the Eighth Asia-Pacific Conference on Wind Engineering, 2013
This study addresses the issues pertinent to both the topographic effects on wind flow fields over complex terrain and the accuracy of computational fluid dynamics (CFD). The numerical simulations using isotropic eddy viscosity and wall functions are conducted based on the numerical solutions of the incompressible, nonisothermal, steady-state turbulent flows, in which a regional computational model of a hilly island in Hong Kong has been constructed and the computational results are compared with the experimental data of a boundary layer wind tunnel testing and the in-situ measurements from a remote sensing facility (Doppler radar wind profiler system) at Cheung Chau (CCH) weather station in the island.
Validation of the simpleFoam (RANS) solver for the atmospheric boundary layer in complex terrain
We validate the simpleFoam (RANS) solver in OpenFOAM (version 2.1.1) for simulating neutral atmospheric boundary layer flows in complex terrain. Initial and boundary conditions are given using Richards and Hoxey proposal [1]. In order to obtain stable simulation of the ABL, modified wall functions are used to set the near-wall boundary conditions, following Blocken et al remedial measures [2]. A structured grid is generated with the new library terrainBlockMesher [3, 4], based on OpenFOAM’s blockMesh native mesher. The new tool is capable of adding orographic features and the forest canopy. Additionally, the mesh can be refined in regions with complex orography. We study both the classical benchmark case of Askervein hill [5] and the more recent Bolund island data set [6]. Our purpose is two-folded: to validate the performance of OpenFOAM steady state solvers, and the suitability of the new meshing tool to generate high quality structured meshes, which will be used in the future for performing more computationally intensive LES simulations in complex terrain.
Numerical Evaluation of Wind Flow over Complex Terrain: Review
Journal of Aerospace Engineering, 2004
This paper reviews the current state of the art in the numerical evaluation of wind flow over different types of topographies. Numerical simulations differing from one another by the type of numerical formulation followed, the turbulence model used, the type of boundary conditions applied, the type of grids adopted, and the type of terrain considered are summarized. A comparative study among numerical and experimental (both wind tunnel and field) existing works establishing the modifications of wind flow over hills, escarpments, valleys, and other complex terrain configurations demonstrates generally good predictions on the upstream but problematic predictions on the downstream areas of the complex terrain. Comparisons are also made with provisions of the current wind standards as well as with speed-up values calculated using guidelines derived from theoretical models.
Boundary-layer Meteorology, 1993
Two mass consistent models (MATHEW and MINERVE) and two dynamic linearized models (MS3DJH/3R and FLOWSTAR) are used to simulate the mean flow over two-dimensional hills of analytical shape and of varying slope. The results are compared with detailed wind tunnel data (RUSHIL experiment at US EPA). Different numerical experiments have been performed, varying input data and control parameters, to test the data-processing methodology and to evaluate the minimum input data (for mass consistent models only) necessary to obtain a reliable flow field. The models behave differently according to the physical assumptions made and numerical procedure used: an assessment is then made in order to identify the proper solution for the different conditions of topography and wind data.
Flow Simulation Over a Two-Dimensional Model Hill
2017
The paper presents the influence of different numerical models as well as of different input parameters for the evaluation of the flow in the simulated atmospheric boundary layer. One important aspect that was tested is the solver’s ability to reproduce recirculation. We compared the numerical velocity distributions in ten vertical sections using different k-ε models with the corresponding data from experiments and we obtained a good agreement. Then we have compared the turbulent kinetic energy distributions in the same sections. Furthermore, we performed a grid dependence and density test to determine the most economic grid that permits a similar result.