Implementation Issues in 3D Wind Flow Predictions Over Complex Terrain

2006 ◽  
Vol 128 (4) ◽  
pp. 539-553 ◽  
Author(s):  
John Prospathopoulos ◽  
Spyros G. Voutsinas
Keyword(s):  
Wind Energy ◽  
Boundary Conditions ◽  
Complex Terrain ◽  
Flow Direction ◽  
Region Of Interest ◽  
Field Measurements ◽  
Navier Stokes ◽  
Wind Flow ◽  
Computational Domain

Practical aspects concerning the use of 3D Navier-Stokes solvers as prediction tools for micro-siting of wind energy installations are considered. Micro-siting is an important issue for a successful application of wind energy in sites of complex terrain. There is a constantly increasing interest in using mean wind flow predictions based on Reynolds averaged Navier-Stokes (RANS) solvers in order to minimize the number of required field measurements. In this connection, certain numerical aspects, such as the extent of the numerical flow domain, the choice of the appropriate inflow boundary conditions, and the grid resolution, can decisively affect the quality of the predictions. In the present paper, these aspects are analyzed with reference to the Askervein hill data base of full scale measurements. The objective of the work is to provide guidelines with respect to the definition of appropriate boundary conditions and the construction of an adequate and effective computational grid when a RANS solver is implemented. In particular, it is concluded that (a) the ground roughness affects the predictions significantly, (b) the computational domain should have an extent permitting the full development of the flow before entering the region of interest, and (c) the quality of the predictions at the local altitude maxima depends on the grid density in the main flow direction.

scholarly journals Evaluation of the lattice Boltzmann method for wind modelling in complex terrain

2020 ◽  
Vol 5 (4) ◽  
pp. 1507-1519
Author(s):  
Alain Schubiger ◽  
Sarah Barber ◽  
Henrik Nordborg
Keyword(s):  
Wind Energy ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Complex Terrain ◽  
Navier Stokes ◽  
Wind Flow ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Boltzmann Method ◽  
Wind Resource

Abstract. The worldwide expansion of wind energy is making the choice of potential wind farm locations more and more difficult. This results in an increased number of wind farms being located in complex terrain, which is characterised by flow separation, turbulence and high shear. Accurate modelling of these flow features is key for wind resource assessment in the planning phase, as the exact positioning of the wind turbines has a large effect on their energy production and lifetime. Wind modelling for wind resource assessments is usually carried out with the linear model Wind Atlas Analysis and Application Program (WAsP), unless the terrain is complex, in which case Reynolds-averaged Navier–Stokes (RANS) solvers such as WindSim and Ansys Fluent are usually applied. Recent research has shown the potential advantages of large-eddy simulation (LES) for modelling the atmospheric boundary layer and thermal effects; however, LES is far too computationally expensive to be applied outside the research environment. Another promising approach is the lattice Boltzmann method (LBM), a computational fluid technique based on the Boltzmann transport equation. It is generally used to study complex phenomena such as turbulence, because it describes motion at the mesoscopic level in contrast to the macroscopic level of conventional computational fluid dynamics (CFD) approaches, which solve the Navier–Stokes (N–S) equations. Other advantages of the LBM include its efficiency; near-ideal scalability on high-performance computers (HPCs); and ability to easily automate the geometry, the mesh generation and the post-processing. However, the LBM has been applied very little to wind modelling in complex terrain for wind energy applications, mainly due to the lack of availability of easy-to-use tools as well as the lack of experience with this technique. In this paper, the capabilities of the LBM to model wind flow around complex terrain are investigated using the Palabos framework and data from a measurement campaign from the Bolund Hill experiment in Denmark. Detached-eddy simulation (DES) and LES in Ansys Fluent are used as a numerical comparison. The results show that there is in general a good agreement between simulation and experimental data, and the LBM performs better than RANS and DES. Some deviations can be observed near the ground, close to the top of the cliff and on the lee side of the hill. The computational costs of the three techniques are compared, and it has been shown that the LBM can perform up to 5 times faster than DES, even though the set-up was not optimised in this initial study. It can be summarised that the LBM has a very high potential for modelling wind flow over complex terrain accurately and at relatively low costs, compared to solving N–S equations conventionally. Further studies on other sites are ongoing.

scholarly journals Evaluation of the Lattice Boltzmann Method for wind modelling in complex terrain

2020 ◽  
Author(s):  
Alain Schubiger ◽  
Sarah Barber ◽  
Henrik Nordborg
Keyword(s):  
Wind Energy ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Complex Terrain ◽  
Navier Stokes ◽  
Wind Flow ◽  
Numerical Comparison ◽  
Ansys Fluent ◽  
Boltzmann Method ◽  
Wind Resource

Abstract. The worldwide expansion of wind energy is making the choice of potential wind farm locations more and more difficult. This results in an increased number of wind farms being located in complex terrain, which is characterised by flow separation, turbulence and high shear. Accurate modelling of these flow features is key for wind resource assessment in the planning phase, as the exact positioning of the wind turbines has a large effect on their energy production and life time. Wind modelling for wind resource assessments is usually carried out with the linear model WAsP, unless the terrain is complex, in which case Reynolds-Averaged Navier-Stokes (RANS) solvers such as WindSim and ANSYS Fluent are usually applied. Recent research has shown the potential advantages of Large Eddy Simulations (LES) for modelling the atmospheric boundary layer and thermal effects; however, LES is far too computationally expensive to be applied outside the research environment. Another promising approach is the Lattice Boltzmann Method (LBM), a computational fluid technique based on the Boltzmann transport equation. It is generally used to study complex phenomena such as turbulence, because it describes motion at the microscopic level in contrast to the macroscopic level of conventional Computational Fluid Dynamics (CFD) approaches, which solve the Navier-Stokes (N-S) equations. Other advantages of LBM include its efficiency, near ideal scalability on High Performance Computers (HPC) and its ability to easily automate the geometry, the mesh generation and the post-processing of the geometry. However, LBM has not yet been applied to wind modelling in complex terrain for wind energy applications, mainly due to the lack of availability of easy-to-use tools as well as the lack of experience with this technique. In this paper, the capabilities of LBM to model wind flow around complex terrain are investigated using the Palabos framework and data from a measurement campaign from the Bolund Hill experiment in Denmark. Detached Eddy Simulations (DES) and LES in ANSYS Fluent are used as a numerical comparison. The results show that there is in general a good agreement between simulation and experimental data, and LBM performs better than RANS and DES. Some deviations can be observed near the ground, close to the top of cliff and on the lee side of the hill. The computational costs of the three techniques are compared and it has been shown that LBM can perform up to 5 times faster than DES, even though the set-up was not optimised in this initial study. It can be summarised that LBM has a very high potential for modelling wind flow over complex terrain accurately and at relatively low costs, compared to solving the N-S conventionally. Further studies on other sites are ongoing.

Spectral Method for Analyzing Motions of Ellis Fluid Over Corrugated Boundaries

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
M. Fazel Bakhsheshi ◽  
J. M. Floryan ◽  
P. N. Kaloni
Keyword(s):  
Boundary Conditions ◽  
Spectral Method ◽  
Transverse Direction ◽  
Flow Direction ◽  
Immersed Boundary ◽  
Computational Domain ◽  
Physical Domain ◽  
Planar Channel ◽  
Spectral Accuracy ◽  
Fourier Expansions

A spectral method for solving the steady flow of a shear-thinning Ellis fluid is discussed for the case of a planar channel with corrugated boundaries. Polynomial approximations are employed for the velocity and viscosity distributions in the regions around singularities. The proposed algorithm employs a fixed computational domain with the physical domain of interest submerged inside the computational domain. The flow boundary conditions are imposed using the concept of immersed boundary conditions. The method, thus, eliminates the need for grid generation. The algorithm relies on Fourier expansions in the flow direction and Chebyshev expansions in the transverse direction. Various tests confirm spectral accuracy of the algorithm.

Wind Flow Over a Complex Terrain in Nygårdsfjell, Norway

2015 ◽  
Author(s):  
Muhammad Bilal ◽  
Narendran Sridhar ◽  
Guillermo Araya ◽  
Sivapathas Parameswaran ◽  
Yngve Birkelund
Keyword(s):  
Wind Energy ◽  
Wind Turbine ◽  
Complex Terrain ◽  
Wind Farm ◽  
Turbulence Models ◽  
Future Research ◽  
Wind Flow ◽  
Governing Equations ◽  
The North ◽  
Numerical Predictions

The understanding of atmospheric flows is crucial in the analysis of dispersion of a contaminant or pollutant, wind energy and air-quality assessment to name a few. Additionally, the effects of complex terrain and associated orographic forcing are crucial in wind energy production. Furthermore, the use of the Reynolds-averaged Navier-Stokes (RANS) equations in the analysis of complex terrain is still considered the “workhorse” since millions of mesh points are required to accurately capture the details of the surface. On the other hand, solving the same problem by means of the instantaneous governing equations of the flow (i.e., in a suite of DNS or LES) would imply almost prohibitive computational resources. In this study, numerical predictions of atmospheric boundary layers are performed over a complex topography located in Nygårdsfjell, Norway. The Nygårdsfjell wind farm is located in a valley at approximately 420 meters above sea level surrounded by mountains in the north and south near the Swedish border. Majority of the winds are believed to be originated from Torneträsk lake in the east which is covered with ice during the winter time. The air closest to the surface on surrounding mountains gets colder and denser. The air then slides down the hill and accumulates over the lake. Later, the air spills out westward towards Ofotfjord through the broader channel that directs and transforms it into highly accelerated winds. Consequently, one of the objectives of the present article is to study the influence of local terrain on shaping these winds over the wind farm. It is worth mentioning that we are not considering any wind turbine model in the present investigation, being the main purpose to understand the influence of the local surface topography and roughness on the wind flow. Nevertheless, future research will include modeling the presence of a wind turbine and will be published elsewhere. The governing equations of the flow are solved by using a RANS approach and by considering three different two-equation turbulence models: k-omega (k–ω), k-epsilon (k–ε) and shear stress transport (SST). Furthermore, the real topographical characteristics of the terrain have been modeled by extracting the required area from the larger digital elevation model (DEM) spanning over 100 km square. The geometry is then extruded using Rhino and meshed in ANSYS Fluent. The terrain dimensions are approximately 2000×1000 meter square.

Computation of Rarefied Gaseous Flows in Micro to Nano Scale Channels With Slip to Transient Regimes Using General Second-Order Quadratic Elements

2008 ◽  
Author(s):  
M. Darbandi ◽  
Y. Daghighi
Keyword(s):  
Boundary Conditions ◽  
Finite Volume ◽  
Higher Order ◽  
Second Order ◽  
Navier Stokes ◽  
Computational Domain ◽  
Slip Boundary Conditions ◽  
Slip Boundary ◽  
Nano Scale ◽  
Transient Regimes

A new finite-volume-based finite-element method using the quadratic elements is developed in the present study, to analyze the flow in micro and nano sizes with higher-order slip boundary conditions. The method is applied to gaseous flow in micro and nanoscale-channels. The developed method is carried out over a wide range of Knudsen numbers, which cover not only the continuum slip flow regime with 0≤Kn≤0.1 but also it entire the range of transient regime with 0.1<Kn≤10. To make the present computational model capable of simulating micro and nano sizes with the help of the Navier-Stokes equations, the modified high-order slip boundary conditions are applied which need utilizing the advantages of general quadratic second order elements in the computational domain. In other words, this paper introduces a new developed method, which is applied on higher-order elements, and employing reliable boundary conditions that all of these issues are used for the first time in the Micro/Nano study as well. The results reveal excellent agreement with those represented by analytical, DSMC, and Boltzmann calculations. The proposed method (using finite-volume-element strategy which benefits from the advantages of general quadratic second-order elements) is proved to be an efficient, practical, and accurate tool, which robustly extends the capability of our primitive large scale Navier-Stokes solver to micro and nano-scale flow predictions in slip and transient regimes. It can be regarded as a super alternative to classical molecular dynamics-based methods.

A Simplified CFD Model With Multi-Periodic Boundary Conditions for Cross Wavy Channels

2011 ◽  
Author(s):  
L. X. Du ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Periodic Boundary ◽  
Flow Direction ◽  
Wave Length ◽  
Three Dimensional ◽  
Periodic Boundary Conditions ◽  
Navier Stokes ◽  
The Cross ◽  
Wavy Channels

The compact and efficient primary surface heat exchangers are often used as recuperators in microturbine regenerative cycle systems. In the present study, the flow and the heat transfer performance of the cross wavy (CW) ducts have been simulated by three-dimensional models. The hydrodynamic diameters of the models are 1.689mm. Navier-Stokes and energy equations are solved by COMSOL3.5. Because one single wavy cell will overlap more than one adjacent channel, multi-periodic boundary conditions are especially adopted to simplify the calculations. Multi-periodic boundary conditions have been proved to have more reasonable flow field and heat transfer coefficient compared with the literature results. A dimensionless parameter L/A (wave length L, internal height of the corrugation in flow direction A) is defined as the optimization target. The numerical results indicated that when L/A = 6, the CW channel has the best comprehensive performance in all the cases. The comprehensive performances of the CW ducts are evaluated by the j/f (heat transfer factor j and friction factor f). The flow and heat transfer characteristics are much more complex in the cross wavy channels, especially when L/A is small.

scholarly journals Numerical Modeling of Jet at the Bottom of Tank at Moderate Reynolds Number Using Compact Hermitian Finite Differences Method

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 63
Author(s):  
Mohammed Loukili ◽  
Kamila Kotrasova ◽  
Denys Dutykh
Keyword(s):  
Finite Differences ◽  
Stokes Equations ◽  
Flow Direction ◽  
Numerical Code ◽  
Navier Stokes ◽  
Computational Domain ◽  
Numerical Resolution ◽  
Moderate Reynolds Number ◽  
Finite Differences Method ◽  
High Reynolds

In this manuscript, the injection of a homogeneous jet in a numerical tank is considered to revolve around discussing the limitation of the direct numerical simulation (DNS), to resolve the equations governing the problem of a jet emitted from the bottom of a numerical tank. The investigation has been made in the context of an unsteady, viscous, and incompressible fluid. The numerical resolution of the equations governing the problem is made by the compact Hermitian finite differences method (HFDM) high accuracy Oh2,h4 First, the numerical code used in this work is validated by comparing the profiles of the velocity components at the median of the lid-driven cavity with the results of the literature. Furthermore, to confirm the validity of the present numerical code, an evaluation of mesh domain sensitivity is assessed by comparing the numerical vertical velocity profiles for different steps of y-direction (flow direction) with the analytical solution. Afterward, the aim is to perform the nonlinear simulations of the Navier–Stokes equations in a large computational domain. Next, the goal is to characterize the instabilities associated with high Reynolds numbers when a jet is emitted from the bottom of the numerical tank.

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