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Title: Imposing land-surface fluxes at an immersed boundary for improved simulations of atmospheric flow over complex terrain

Abstract

Boundary layer flows are greatly complicated by the presence of complex terrain which redirects mean flow and alters the structure of turbulence. Surface fluxes of heat and moisture provide additional forcing which induce secondary flows, or can dominate flow dynamics in cases with weak mean flows. Mesoscale models are increasingly being used for numerical simulations of boundary layer flows over complex terrain. These models typically use a terrain-following coordinate transformation, but these introduce numerical errors over steep terrain. An alternative is to use an immersed boundary method which alleviates errors associated with the coordinate transformation by allowing the terrain to be represented as a surface which arbitrarily passes through a Cartesian grid. This paper describes coupling atmospheric physics models to an immersed boundary method implemented in the Weather Research and Forecasting (WRF) model in previous work [Lundquist et al., 2007]. When the immersed boundary method is used, boundary conditions must be imposed on the immersed surface for velocity and scalar surface fluxes. Previous algorithms, such as those used by Tseng and Ferziger [2003] and Balaras [2004], impose no-slip boundary conditions on the velocity field at the immersed surface by adding a body force to the Navier-Stokes equations. Flux boundary conditionsmore » for the advection-diffusion equation have not been adequately addressed. A new algorithm is developed here which allows scalar surface fluxes to be imposed on the flow solution at an immersed boundary. With this extension of the immersed boundary method, land-surface models can be coupled to the immersed boundary to provide realistic surface forcing. Validation is provided in the context of idealized valley simulations with both specified and parameterized surface fluxes using the WRF code. Applicability to real terrain is illustrated with a fully coupled two-dimensional simulation of the Owens Valley in California.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
945647
Report Number(s):
LLNL-CONF-404513
TRN: US200903%%697
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: 18th Symposium on Boundary Layers and Turbulence, Stockholm, Sweden, Jun 09 - Jun 13, 2008
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; ALGORITHMS; BOUNDARY CONDITIONS; BOUNDARY LAYERS; COMPLEX TERRAIN; FORECASTING; MOISTURE; NAVIER-STOKES EQUATIONS; PHYSICS; SCALARS; SIMULATION; TRANSFORMATIONS; TURBULENCE; VALIDATION; VELOCITY; WEATHER

Citation Formats

Lundquist, K A, Chow, F K, Lundquist, J K, and Mirocha, J D. Imposing land-surface fluxes at an immersed boundary for improved simulations of atmospheric flow over complex terrain. United States: N. p., 2008. Web.
Lundquist, K A, Chow, F K, Lundquist, J K, & Mirocha, J D. Imposing land-surface fluxes at an immersed boundary for improved simulations of atmospheric flow over complex terrain. United States.
Lundquist, K A, Chow, F K, Lundquist, J K, and Mirocha, J D. 2008. "Imposing land-surface fluxes at an immersed boundary for improved simulations of atmospheric flow over complex terrain". United States. https://www.osti.gov/servlets/purl/945647.
@article{osti_945647,
title = {Imposing land-surface fluxes at an immersed boundary for improved simulations of atmospheric flow over complex terrain},
author = {Lundquist, K A and Chow, F K and Lundquist, J K and Mirocha, J D},
abstractNote = {Boundary layer flows are greatly complicated by the presence of complex terrain which redirects mean flow and alters the structure of turbulence. Surface fluxes of heat and moisture provide additional forcing which induce secondary flows, or can dominate flow dynamics in cases with weak mean flows. Mesoscale models are increasingly being used for numerical simulations of boundary layer flows over complex terrain. These models typically use a terrain-following coordinate transformation, but these introduce numerical errors over steep terrain. An alternative is to use an immersed boundary method which alleviates errors associated with the coordinate transformation by allowing the terrain to be represented as a surface which arbitrarily passes through a Cartesian grid. This paper describes coupling atmospheric physics models to an immersed boundary method implemented in the Weather Research and Forecasting (WRF) model in previous work [Lundquist et al., 2007]. When the immersed boundary method is used, boundary conditions must be imposed on the immersed surface for velocity and scalar surface fluxes. Previous algorithms, such as those used by Tseng and Ferziger [2003] and Balaras [2004], impose no-slip boundary conditions on the velocity field at the immersed surface by adding a body force to the Navier-Stokes equations. Flux boundary conditions for the advection-diffusion equation have not been adequately addressed. A new algorithm is developed here which allows scalar surface fluxes to be imposed on the flow solution at an immersed boundary. With this extension of the immersed boundary method, land-surface models can be coupled to the immersed boundary to provide realistic surface forcing. Validation is provided in the context of idealized valley simulations with both specified and parameterized surface fluxes using the WRF code. Applicability to real terrain is illustrated with a fully coupled two-dimensional simulation of the Owens Valley in California.},
doi = {},
url = {https://www.osti.gov/biblio/945647}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jun 05 00:00:00 EDT 2008},
month = {Thu Jun 05 00:00:00 EDT 2008}
}

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