Large Eddy Simulations Of Atmospheric Flows Over Idealized And Realistic Double Hill Terrain In The Wrf Model

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Large Eddy Simulations Of Atmospheric Flows Over Idealized And Realistic Double Hill Terrain In The Wrf Model

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Author : Yayun Qiao
language : en
Publisher:
Release Date : 2020

Large Eddy Simulations Of Atmospheric Flows Over Idealized And Realistic Double Hill Terrain In The Wrf Model written by Yayun Qiao and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with Atmospheric circulation categories.

Airflow over complex terrain throughout the atmospheric boundary layer (ABL) governs the transport and mixing of mass, momentum, and heat. Topography causes obstruction of the airflow and generates airflow distortion and turbulence. Perturbations in land-atmosphere interactions cause various weather phenomena like cold-air pools (CAPs) leading to changes in many aspects of weather and climate that impact the optimal position of wind-turbine, forest-fire behavior, and forecasting, as well as trace-gas and pollutant dispersion. This thesis investigates the flow over complex terrain, specifically double-hill terrain, with new numerical model approaches. The first study utilizes the Weather Research and Forecasting (WRF) model with large eddy simulations (LES) and the immersed-boundary method (IBM) to improve the simulations of the flow and recirculation regions over steep double-hill terrain. The gap distance controls the flow distribution behind both hills. The upwind hill has a significant influence on the second hill. When the gap distance is too small, the flow after the upwind hill cannot regain its momentum. The second study examines the flow distribution over a forested double-hill and the impact of the gap distance between two hills on scalar transport (CO2 and H2O). This study uses the WRF-LES model coupled with a new multiple-layer canopy module (MCANOPY module). We find that flow recirculation is the primary factor dominating scalar transport. Scalars are transported and trapped in both recirculation regions and accumulated on the lee sides of both hills. Our simulation shows the occurrence of two vortices on the lee side of the upstream hill enhances the accumulation of scalars in the valleys. In the end, we extend our work from the first study to understand flow patterns over a realistic double-hill topography. Results show that the valley gap distance is so small that the recirculation region in the valley between two hills cannot fully develop. Additionally, the WRF-IBM captures the structure of microscale flows that other models have not captured in the previous studies.

Large Eddy Simulation Of The Nighttime Stable Atmospheric Boundary Layer

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Author : Bowen Zhou
language : en
Publisher:
Release Date : 2012

Large Eddy Simulation Of The Nighttime Stable Atmospheric Boundary Layer written by Bowen Zhou and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.

A stable atmospheric boundary layer (ABL) develops over land at night due to radiative surface cooling. The state of turbulence in the stable boundary layer (SBL) is determined by the competing forcings of shear production and buoyancy destruction. When both forcings are comparable in strength, the SBL falls into an intermittently turbulent state, where intense turbulent bursts emerge sporadically from an overall quiescent background. This usually occurs on clear nights with weak winds when the SBL is strongly stable. Although turbulent bursts are generally short-lived (half an hour or less), their impact on the SBL is significant since they are responsible for most of the turbulent mixing. The nighttime SBL can be modeled with large-eddy simulation (LES). LES is a turbulence-resolving numerical approach which separates the large-scale energy-containing eddies from the smaller ones based on application of a spatial filter. While the large eddies are explicitly resolved, the small ones are represented by a subfilter-scale (SFS) stress model. Simulation of the SBL is more challenging than the daytime convective boundary layer (CBL) because nighttime turbulent motions are limited by buoyancy stratification, thus requiring fine grid resolution at the cost of immense computational resources. The intermittently turbulent SBL adds additional levels of complexity, requiring the model to not only sustain resolved turbulence during quiescent periods, but also to transition into a turbulent state under appropriate conditions. As a result, LES of the strongly stable SBL potentially requires even finer grid resolution, and has seldom been attempted. This dissertation takes a different approach. By improving the SFS representation of turbulence with a more sophisticated model, intermittently turbulent SBL is simulated, to our knowledge, for the first time in the LES literature. The turbulence closure is the dynamic reconstruction model (DRM), applied under an explicit filtering and reconstruction LES framework. The DRM is a mixed model that consists of subgrid scale (SGS) and resolved subfilter scale (RSFS) components. The RSFS portion is represented by a scale-similarity model that allows for backscatter of energy from the SFS to the mean flow. Compared to conventional closures, the DRM is able to sustain resolved turbulence under moderate stability at coarser resolution (thus saving computational resources). The DRM performs equally well at fine resolution. Under strong stability, the DRM simulates an intermittently turbulent SBL, whereas conventional closures predict false laminar flows. The improved simulation methodology of the SBL has many potential applications in the area of wind energy, numerical weather prediction, pollution modeling and so on. The SBL is first simulated over idealized flat terrain with prescribed forcings and periodic lateral boundaries. A wide range of stability regimes, from weakly to strongly stable conditions, is tested to evaluate model performance. Under strongly stable conditions, intermittency due to mean shear and turbulence interactions is simulated and analyzed. Furthermore, results of the strongly stable SBL are used to improve wind farm siting and nighttime operations. Moving away from the idealized setting, the SBL is simulated over relatively flat terrain at a Kansas site over the Great Plains, where the Cooperative Atmospheric-Surface Exchange Study - 1999 (CASES-99) took place. The LES obtains realistic initial and lateral boundary conditions from a meso-scale model reanalysis through a grid nesting procedure. Shear-instability induced intermittency observed on the night of Oct 5th during CASES-99 is reproduced to good temporal and magnitude agreement. The LES locates the origin of the shear-instability waves in a shallow upwind valley, and uncovers the intermittency mechanism to be wave breaking over a standing wave (formed over a stagnant cold-air bubble) across the valley. Finally, flow over the highly complex terrain of the Owens Valley in California is modeled with a similar nesting procedure. The LES results are validated with observation data from the 2006 Terrain-Induced Rotor Experiment (T-REX). The nested LES reproduces a transient nighttime warming event observed on the valley floor on April 17 during T-REX. The intermittency mechanism is shown to be through slope-valley flow transitions. In addition, a cold-air intrusion from the eastern valley sidewall is simulated. This generates an easterly cross-valley flow, and the associated top-down mixing through breaking Kelvin-Helmholtz billows is analyzed. Finally, the nesting methodology tested and optimized in the CASES-99 and T-REX studies is transferrable to general ABL applications. For example, a nested LES is performed to model daytime methane plume dispersion over a landfill and good results are obtained.

Large Eddy Simulation Of Atmospheric Boundary Layer Flow Over A Realistic Urban Surface

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Author : Marco Giovanni Giometto
language : en
Publisher:
Release Date :

Large Eddy Simulation Of Atmospheric Boundary Layer Flow Over A Realistic Urban Surface written by Marco Giovanni Giometto and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on with categories.

Large Eddy Simulation For Compressible Flows

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Author : Eric Garnier
language : en
Publisher: Springer Science & Business Media
Release Date : 2009-08-11

Large Eddy Simulation For Compressible Flows written by Eric Garnier and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009-08-11 with Science categories.

This book addresses both the fundamentals and the practical industrial applications of Large Eddy Simulation (LES) in order to bridge the gap between LES research and the growing need to use it in engineering modeling.

Large Eddy Simulation For Incompressible Flows

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Author : P. Sagaut
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-04-18

Large Eddy Simulation For Incompressible Flows written by P. Sagaut and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-04-18 with Science categories.

First concise textbook on Large-Eddy Simulation, a very important method in scientific computing and engineering From the foreword to the third edition written by Charles Meneveau: "... this meticulously assembled and significantly enlarged description of the many aspects of LES will be a most welcome addition to the bookshelves of scientists and engineers in fluid mechanics, LES practitioners, and students of turbulence in general."

Large Eddy Simulation Of Atmospheric Flow Over Complex Terrain

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Author : Andreas Bechmann
language : en
Publisher:
Release Date : 2006

Large Eddy Simulation Of Atmospheric Flow Over Complex Terrain written by Andreas Bechmann and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.

Large Eddy Simulation Of Complex Engineering And Geophysical Flows

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Author : Boris Galperin
language : en
Publisher: Cambridge University Press
Release Date : 1993-11-26

Large Eddy Simulation Of Complex Engineering And Geophysical Flows written by Boris Galperin and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1993-11-26 with Technology & Engineering categories.

Originally published in 1993, this book was the first to offer a comprehensive review of large eddy simulations (LES) - the history, state of the art, and promising directions for research. Among topics covered are fundamentals of LES; LES of incompressible, compressible, and reacting flows; LES of atmospheric, oceanic, and environmental flows; and LES and massivelt parallel computing. The book grew out of an international workshop that, for the first time, brought together leading researchers in engineering and geophysics to discuss developments and applications of LES models in their respective fields. It will be of value to anyone with an interest in turbulence modelling.

Direct And Large Eddy Simulation I

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Author : Peter R. Voke
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-12-06

Direct And Large Eddy Simulation I written by Peter R. Voke and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-12-06 with Technology & Engineering categories.

It is a truism that turbulence is an unsolved problem, whether in scientific, engin eering or geophysical terms. It is strange that this remains largely the case even though we now know how to solve directly, with the help of sufficiently large and powerful computers, accurate approximations to the equations that govern tur bulent flows. The problem lies not with our numerical approximations but with the size of the computational task and the complexity of the solutions we gen erate, which match the complexity of real turbulence precisely in so far as the computations mimic the real flows. The fact that we can now solve some turbu lence in this limited sense is nevertheless an enormous step towards the goal of full understanding. Direct and large-eddy simulations are these numerical solutions of turbulence. They reproduce with remarkable fidelity the statistical, structural and dynamical properties of physical turbulent and transitional flows, though since the simula tions are necessarily time-dependent and three-dimensional they demand the most advanced computer resources at our disposal. The numerical techniques vary from accurate spectral methods and high-order finite differences to simple finite-volume algorithms derived on the principle of embedding fundamental conservation prop erties in the numerical operations. Genuine direct simulations resolve all the fluid motions fully, and require the highest practical accuracy in their numerical and temporal discretisation. Such simulations have the virtue of great fidelity when carried out carefully, and repre sent a most powerful tool for investigating the processes of transition to turbulence.

Direct And Large Eddy Simulation

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Author : Bernard J. Geurts
language : en
Publisher: Walter de Gruyter GmbH & Co KG
Release Date : 2022-12-05

Direct And Large Eddy Simulation written by Bernard J. Geurts and has been published by Walter de Gruyter GmbH & Co KG this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022-12-05 with Mathematics categories.

This book presents a comprehensive overview of the mathematics and physics behind the simulation of turbulent flows and discusses in detail (i) the phenomenology of turbulence in fluid dynamics, (ii) the role of direct and large-eddy simulation in predicting these dynamics, (iii) the multiple considerations underpinning subgrid modelling, and, (iv) the issue of validation and reliability resulting from interacting modelling and numerical errors.

Direct And Large Eddy Simulation X

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Author : Dimokratis G.E. Grigoriadis
language : en
Publisher: Springer
Release Date : 2017-10-06

Direct And Large Eddy Simulation X written by Dimokratis G.E. Grigoriadis and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017-10-06 with Technology & Engineering categories.

This book addresses nearly all aspects of the state of the art in LES & DNS of turbulent flows, ranging from flows in biological systems and the environment to external aerodynamics, domestic and centralized energy production, combustion, propulsion as well as applications of industrial interest. Following the advances in increased computational power and efficiency, several contributions are devoted to LES & DNS of challenging applications, mainly in the area of turbomachinery, including flame modeling, combustion processes and aeroacoustics. The book includes work presented at the tenth Workshop on 'Direct and Large-Eddy Simulation' (DLES-10), which was hosted in Cyprus by the University of Cyprus, from May 27 to 29, 2015. The goal of the workshop was to establish a state of the art in DNS, LES and related techniques for the computation and modeling of turbulent and transitional flows. The book is of interest to scientists and engineers, both in the early stages of their career and at a more senior level.