scholarly journals A Multi-Fidelity Framework for Wildland Fire Behavior Simulations over Complex Terrain

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 273
Author(s):  
Marcos Vanella ◽  
Kevin McGrattan ◽  
Randall McDermott ◽  
Glenn Forney ◽  
William Mell ◽  
...  
Keyword(s):  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Vegetation Type ◽  
Wildland Fire ◽  
Fire Behavior ◽  
Chemical Species ◽  
Fire Spread ◽  
Immersed Boundary ◽  
Finite Volume Scheme ◽  
Boundary Method

A method for the large-eddy simulation (LES) of wildfire spread over complex terrain is presented. In this scheme, a cut-cell immersed boundary method (CC-IBM) is used to render the complex terrain, defined by a tessellation, on a rectilinear Cartesian grid. Discretization of scalar transport equations for chemical species is done via a finite volume scheme on cut-cells defined by the intersection of the terrain geometry and the Cartesian cells. Momentum transport and heat transfer close to the immersed terrain are handled using dynamic wall models and a direct forcing immersed boundary method. A new “open” convective inflow/outflow method for specifying atmospheric wind boundary conditions is presented. Additionally, three basic approaches have been explored to model fire spread: (1) Representing the vegetation as a collection of Lagrangian particles, (2) representing the vegetation as a semi-porous boundary, and (3) representing the fire spread using a level set method, in which the fire spreads as a function of terrain slope, vegetation type, and wind speed. Several test and validation cases are reported to demonstrate the capabilities of this novel wildfire simulation methodology.

An Immersed Boundary Method for Simulation of Wind Flow Over Complex Terrain

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
S. Jafari ◽  
N. Chokani ◽  
R. S. Abhari
Keyword(s):  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Stokes Equations ◽  
Ground Level ◽  
Rectangular Domain ◽  
Immersed Boundary ◽  
Test Case ◽  
Wind Flow ◽  
Wall Functions ◽  
Boundary Method

The accurate modeling of the wind resource over complex terrain is required to optimize the micrositing of wind turbines. In this paper, an immersed boundary method that is used in connection with the Reynolds-averaged Navier–Stokes equations with k-ω turbulence model in order to efficiently simulate the wind flow over complex terrain is presented. With the immersed boundary method, only one Cartesian grid is required to simulate the wind flow for all wind directions, with only the rotation of the digital elevation map. Thus, the lengthy procedure of generating multiple grids for conventional rectangular domain is avoided. Wall functions are employed with the immersed boundary method in order to relax the stringent near-wall grid resolution requirements as well as to allow the effects of surface roughness to be accounted for. The immersed boundary method is applied to the complex terrain test case of Bolund Hill. The simulation results of wind speed and turbulent kinetic energy show good agreement with experiments for heights greater than 5 m above ground level.

An Immersed Boundary Method for the Weather Research and Forecasting Model

2010 ◽  
Vol 138 (3) ◽  
pp. 796-817 ◽  
Author(s):  
Katherine A. Lundquist ◽  
Fotini Katopodes Chow ◽  
Julie K. Lundquist
Keyword(s):  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Wrf Model ◽  
Neumann Boundary ◽  
Weather Research And Forecasting ◽  
Immersed Boundary ◽  
Mesoscale Models ◽  
Boundary Method ◽  
Terrain Following ◽  
Weather Research

Abstract This paper describes an immersed boundary method that facilitates the explicit resolution of complex terrain within the Weather Research and Forecasting (WRF) model. Mesoscale models, such as WRF, are increasingly used for high-resolution simulations, particularly in complex terrain, but errors associated with terrain-following coordinates degrade the accuracy of the solution. The use of an alternative-gridding technique, known as an immersed boundary method, alleviates coordinate transformation errors and eliminates restrictions on terrain slope that currently limit mesoscale models to slowly varying terrain. Simulations are presented for canonical cases with shallow terrain slopes, and comparisons between simulations with the native terrain-following coordinates and those using the immersed boundary method show excellent agreement. Validation cases demonstrate the ability of the immersed boundary method to handle both Dirichlet and Neumann boundary conditions. Additionally, realistic surface forcing can be provided at the immersed boundary by atmospheric physics parameterizations, which are modified to include the effects of the immersed terrain. Using the immersed boundary method, the WRF model is capable of simulating highly complex terrain, as demonstrated by a simulation of flow over an urban skyline.

Large-Eddy Simulation over Complex Terrain Using an Improved Immersed Boundary Method in the Weather Research and Forecasting Model

2018 ◽  
Vol 146 (9) ◽  
pp. 2781-2797 ◽  
Author(s):  
Jingyi Bao ◽  
Fotini Katopodes Chow ◽  
Katherine A. Lundquist
Keyword(s):  
Boundary Condition ◽  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Weather Research And Forecasting ◽  
Immersed Boundary ◽  
Flat Terrain ◽  
Boundary Method ◽  
Terrain Following ◽  
Bolund Hill ◽  
Askervein Hill

Abstract The Weather Research and Forecasting (WRF) Model is increasingly being used for higher-resolution atmospheric simulations over complex terrain. With increased resolution, resolved terrain slopes become steeper, and the native terrain-following coordinates used in WRF result in numerical errors and instability. The immersed boundary method (IBM) uses a nonconformal grid with the terrain surface represented through interpolated forcing terms. Lundquist et al.’s WRF-IBM implementation eliminates the limitations of WRF’s terrain-following coordinate and was previously validated with a no-slip boundary condition for urban simulations and idealized terrain. This paper describes the implementation of a log-law boundary condition into WRF-IBM to extend its applicability to general atmospheric complex terrain simulations. The implementation of the improved WRF-IBM boundary condition is validated for neutral flow over flat terrain and the complex terrain cases of Askervein Hill, Scotland, and Bolund Hill, Denmark. First, comparisons are made to similarity theory and standard WRF results for the flat terrain case. Then, simulations of flow over the moderately sloped Askervein Hill are used to demonstrate agreement between the IBM and terrain-following WRF results, as well as agreement with observations. Finally, Bolund Hill simulations show that WRF-IBM can handle steep topography (standard WRF fails) and compares well to observations. Overall, the new WRF-IBM boundary condition shows improved performance, though the leeside representation of the flow can be potentially further improved.

scholarly journals An Immersed Boundary Method Enabling Large-Eddy Simulations of Flow over Complex Terrain in the WRF Model

2012 ◽  
Vol 140 (12) ◽  
pp. 3936-3955 ◽  
Author(s):  
Katherine A. Lundquist ◽  
Fotini Katopodes Chow ◽  
Julie K. Lundquist
Keyword(s):  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Sonic Anemometer ◽  
Three Dimensional ◽  
Wrf Model ◽  
Oklahoma City ◽  
Immersed Boundary ◽  
Field Campaign ◽  
Boundary Method ◽  
Outer Domain

Abstract This paper describes a three-dimensional immersed boundary method (IBM) that facilitates the explicit resolution of complex terrain within the Weather Research and Forecasting (WRF) model. Two interpolation methods—trilinear and inverse distance weighting (IDW)—are used at the core of the IBM algorithm. This work expands on the previous two-dimensional IBM algorithm of Lundquist et al., which uses bilinear interpolation. Simulations of flow over a three-dimensional hill are performed with WRF’s native terrain-following coordinate and with both IB methods. Comparisons of flow fields from the three simulations show excellent agreement, indicating that both IB methods produce accurate results. IDW proves more adept at handling highly complex urban terrain, where the trilinear interpolation algorithm fails. This capability is demonstrated by using the IDW core to model flow in Oklahoma City, Oklahoma, from intensive observation period 3 (IOP3) of the Joint Urban 2003 field campaign. Flow in Oklahoma City is simulated concurrently with an outer domain with flat terrain using one-way nesting to generate a turbulent flow field. Results from the IBM-WRF simulation of IOP3 compare well with observations from the field campaign, as well as with results from an urban computational fluid dynamics code, Finite Element Model in 3-Dimensions and Massively Parallelized (FEM3MP), which used body-fitted coordinates. Using the FAC2 performance metric from Chang and Hanna, which is the fraction of predictions within a factor of 2 of observations, IBM-WRF achieves 100% and 71% for velocity predictions using cup and sonic anemometer observations, respectively. For the passive scalar, 53% of the model predictions meet the FAC5 (factor of 5) criteria.

scholarly journals Mesoscale to Microscale Simulations over Complex Terrain with the Immersed Boundary Method in the Weather Research and Forecasting Model

2020 ◽  
Vol 148 (2) ◽  
pp. 577-595 ◽  
Author(s):  
David J. Wiersema ◽  
Katherine A. Lundquist ◽  
Fotini Katopodes Chow
Keyword(s):  
Boundary Conditions ◽  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Immersed Boundary ◽  
Eddy Simulation ◽  
Boundary Method ◽  
Large Eddy ◽  
Terrain Following

Abstract Improvements to the Weather Research and Forecasting (WRF) Model are made to enable multiscale simulations over highly complex terrain with dynamically downscaled boundary conditions from the mesoscale to the microscale. Over steep terrain, the WRF Model develops numerical errors that are due to grid deformation of the terrain-following coordinates. An alternative coordinate system, the immersed boundary method (IBM), has been implemented into WRF, allowing for simulations over highly complex terrain; however, the new coordinate system precluded nesting within mesoscale simulations using WRF’s native terrain-following coordinates. Here, the immersed boundary method and WRF’s grid-nesting framework are modified to seamlessly work together. This improved framework for the first time allows for large-eddy simulation over complex (urban) terrain with IBM to be nested within a typical mesoscale WRF simulation. Simulations of the Joint Urban 2003 field campaign in Oklahoma City, Oklahoma, are performed using a multiscale five-domain nested configuration, spanning horizontal grid resolutions from 6 km to 2 m. These are compared with microscale-only simulations with idealized lateral boundary conditions and with observations of wind speed/direction and SF6 concentrations from a controlled release from intensive observation period 3. The multiscale simulation, which is configured independent of local observations, shows similar model skill predicting wind speed/direction and improved skill predicting SF6 concentrations when compared with the idealized simulations, which require use of observations to set mean flow conditions. Use of this improved multiscale framework shows promise for enabling large-eddy simulation over highly complex terrain with dynamically downscaled boundary conditions from mesoscale models.

scholarly journals An Immersed Boundary Geometric Preprocessor for Arbitrarily Complex Terrain and Geometry

2015 ◽  
Vol 32 (11) ◽  
pp. 2075-2087 ◽  
Author(s):  
Inanc Senocak ◽  
Micah Sandusky ◽  
Rey DeLeon ◽  
Derek Wade ◽  
Kyle Felzien ◽  
...  
Keyword(s):  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Complex Geometry ◽  
Turbulence Models ◽  
Urban Environments ◽  
Immersed Boundary ◽  
Wind Fields ◽  
Geometric Information ◽  
Distance Field ◽  
Boundary Method

AbstractThere is a growing interest to apply the immersed boundary method to compute wind fields over arbitrarily complex terrain. The computer implementation of an immersed boundary module into an existing flow solver can be accomplished with minor modifications to the rest of the computer program. However, a versatile preprocessor is needed at the first place to extract the essential geometric information pertinent to the immersion of an arbitrarily complex terrain inside a 3D Cartesian mesh. Errors in the geometric information can negatively impact the correct implementation of the immersed boundary method as part of the solution algorithm. Additionally, the distance field from the terrain is needed to implement various subgrid-scale turbulence models and to initialize wind fields over complex terrain. Despite the popularity of the immersed boundary method, procedures used in the geometric preprocessing stage have received less attention. The present study found that concave and convex regions of complex terrain are particularly challenging to process with existing procedures discussed in the literature. To address this issue, a geometric preprocessor with a distance field solver was presented, and the solver demonstrated its versatility for arbitrarily complex geometry, terrain, and urban environments. The distance field solver uses the initial distance field at the immersed boundaries and propagates it to the rest of the domain by solving the Eikonal equation with the fast sweeping method.

scholarly journals Toward a GPU-Accelerated Immersed Boundary Method for Wind Forecasting Over Complex Terrain

2012 ◽  
Author(s):  
Rey DeLeon ◽  
Kyle Felzien ◽  
Inanc Senocak
Keyword(s):  
Immersed Boundary Method ◽  
Complex Terrain ◽  
Prediction Models ◽  
Parallel Implementation ◽  
Weather Prediction ◽  
Immersed Boundary ◽  
Computational Domain ◽  
Flow Solver ◽  
Micro Scale ◽  
Boundary Method

A short-term wind power forecasting capability can be a valuable tool in the renewable energy industry to address load-balancing issues that arise from intermittent wind fields. Although numerical weather prediction models have been used to forecast winds, their applicability to micro-scale atmospheric boundary layer flows and ability to predict wind speeds at turbine hub height with a desired accuracy is not clear. To address this issue, we develop a multi-GPU parallel flow solver to forecast winds over complex terrain at the micro-scale, where computational domain size can range from meters to several kilometers. In the solver, we adopt the immersed boundary method and the Lagrangian dynamic large-eddy simulation model and extend them to atmospheric flows. The computations are accelerated on GPU clusters with a dual-level parallel implementation that interleaves MPI with CUDA. We evaluate the flow solver components against test problems and obtain preliminary results of flow over Bolund Hill, a coastal hill in Denmark.

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