14th Conference on Mountain Meteorology

P2.27

Assessment of explicit filtering and reconstruction turbulence models for large-eddy simulation over complex terrain

Bowen Zhou, Univ. of California, Berkeley, CA; and F. K. Chow

In this study,‭ ‬large-eddy‭ ‬simulation‭ (‬LES‭) ‬is performed over complex terrain for both idealized and real‭ ‬cases.‭ ‬We use an explicit filtering and reconstruction‭ ‬turbulence modeling‭ ‬approach‭ ‬which‭ ‬splits the‭ ‬subfilter-scale‭ (‬SFS‭) ‬turbulence stress into‭ ‬resolvable‭ ‬subfilter-scale‭ (‬RSFS‭) ‬stresses and‭ ‬subgrid-scale‭ (‬SGS‭) ‬stresses.‭ ‬The former are recovered from a velocity reconstruction approach,‭ ‬and the latter are represented by either a TKE-1.5‭ ‬model or a dynamic eddy-viscosity model.‭ ‬This‭ ‬approach has been proven advantageous‭ ‬in our previous work‭ ‬in terms of‭ ‬turbulence representation and‭ ‬agreement with similarity theory‭ ‬in neutral‭ ‬and stable atmospheric‭ ‬boundary layer flow‭ ‬over flat terrain.‭ ‬It has also been successfully applied in LES‭ ‬over Askervein Hill,‭ ‬Scotland,‭ ‬but‭ ‬with certain‭ ‬limitations.‭ ‬In this work,‭ ‬the limits‭ ‬and applicability‭ ‬of the explicit filtering approach are explored‭ ‬using‭ ‬flow‭ ‬over a‭ ‬3D bell shaped mountain.‭ ‬This idealized test case has‭ ‬two objectives:‭ ‬to evaluate the performance and computational cost of reconstruction models with conventional eddy viscosity closures, and to assess the grid aspect ratio and hill slope requirements for using the reconstruction model under a terrain following coordinate system.‭ ‬Using the results from the‭ ‬idealized‭ ‬study as a guideline,‭ ‬we perform LES‭ ‬in‭ Owens Valley,‭ ‬located in the lee of‭ (‬east of‭) ‬the California Sierra Nevada Range,‭ ‬which was the site of the‭ ‬2006‭ ‬Terrain-Induced Rotor Experiment‭ (‬T-REX‭)‬.‭ ‬A set of nested grids are used to resolve the region of interest,‭ ‬beginning with‭ ‬9‭ ‬km‭ ‬horizontal spacing‭ ‬down to a fine grid‭ ‬with‭ ‬350‭ ‬m‭ ‬spacing.‭ ‬At‭ ‬1‭ ‬km and coarser grid levels,‭ ‬the TKE-1.5‭ ‬LES closure‭ ‬is‭ ‬used,‭ ‬as it is more appropriate for such resolutions.‭ ‬The‭ ‬350m grid resolution run is carried out with explicit filtering and reconstruction models.‭ ‬We will‭ ‬evaluate conclusions from the idealized study using‭ ‬this‭ ‬real test case and‭ ‬validate our simulation results using radiosonde‭ ‬and other data from the field campaign.‭ ‬Results‭ ‬with explicit filtering and reconstruction‭ ‬will be compared to‭ ‬conventional LES closure‭ models.‭

Poster Session 2, Wednesday Poster Session
Wednesday, 1 September 2010, 10:00 AM-11:30 AM, Alpine Ballroom B

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