Interfacing Model Components CRTI RD Project Review Meeting Canadian Meteorological Centre August 22-23, 2006

Component 3 : Interfacing of Model Components urbanSTREAM urbanGEM/LAM Component 2 Component 1 2-way interaction ? urbanLS urbanEU Component 4 Component 5 (whole system validation) Component 3 CRTI

Coupling GEM/LAM with urbanSTREAM urbanSTREAM urbanGEM/LAM Component 2 Component 1 2-way interaction ? Component 3 1.urbanGEM/LAM is a mesoscale code from Environment Canada 2.urbanSTREAM is a microscale CFD model Flow models

Regional GEM 15 km OPERATIONAL 48-h RUN (00 or 12 UTC) EVENT GEM-LAM 2.5 km GEM-LAM 1 km MC2-LAM 250 m T+12 T-3 T-6 T-9 21-h run 18-h run 15-h run Microscale flow models IC + LBC Global Variable resolution 576 x 641 Timestep = 7.5 min 58 levels (for NWP) 1D turbulence No TEB LAM 201 x 201 Timestep = 60 s 53 levels (two levels of packing near surface) 1D turbulence TEB LAM 201 x 201 Timestep = 30 s 53 levels (two levels of packing near surface) 1D turbulence TEB LAM 201 x 401 (long axis oriented along the low- level wind direction) Timestep = 10 s 53 levels (two levels of packing near surface) 3D turbulence TEB From Mesoscale to Microscale

Interfacing Mesoscale Model with CFD Model Two major challenges involved in this activity –Synchronization: Running flow solvers simultaneously and maintaining real-time communication between two codes (information exchange) –Exchange: Specify meaningful boundary conditions on basis of exchanged data Mesoscale model (GEM/LAM) functions as URANS Two possible exchange modes between mesoscale model and CFD model requiring two different methodologies –Mesoscale (URANS) to CFD (URANS) Simpler option –Mesoscale (URANS) to CFD (LES) More difficult option –Artificial buffer layer at interface

Two Modes of Exchange From Mesoscale Model to CFD Mesoscale (URANS)CFD (LES) Provide statistically-averaged data Create turbulent fluctuations coarse resolution statistical averages of momentum and turbulence quantities turbulence approximated with model fine resolution generation of quality turbulent eddies according to statistical data supplied by RANS flow solver to dispatch into LES region (“eddy seeding”) Interface Mesoscale (URANS)CFD (URANS) Provide statistically-averaged data coarse resolution prolongation of solution from mesoscale region to CFD region fine resolution restriction of solution from CFD region to mesoscale region Interface Mode 1 (two-way coupling) Mode 2 (two-way coupling) Measurement (Experiment)

Inner region: buildings explicitly resolved Outer region: modelled by drag force B.C. from urbanGEM/LAM One-way coupling (downscaling) (URANS  URANS) urbanSTREAM

Coupling GEM/LAM with urbanSTREAM Multi-resolution decomposition with full overlap One-way coupling algorithm One-way coupling of GEM/LAM (mesoscale model) to urbanSTREAM (CFD model) Solution integrated separately on coarse-level and fine-level domains Coupling enforced by imposing boundary conditions on D f using data coming from coarse grid (mesoscale solution) on D c Coarse resolution field obtained on boundary of D f by simple linear interpolation Prolongation of coarse grid solution at boundary of fine-level domain to various vertical levels obtained from idealized mean velocity and TKE profiles (e.g., three-layer wind model)

Interface Limited Length-Scale k-e Model to Mesoscale Model (GEM/LAM) Inclusion of Coriolis force terms –without Coriolis forces to balance applied pressure gradient at boundary- layer top (where stress divergence vanishes), horizontally homogeneous boundary layer not possible For flow in ABL, need to impose outer scale to limit maximum size of turbulent eddies due to –boundary-layer depth (e.g., ) –stable stratification (e.g., ) Limit turbulent length scale modifying production term in dissipation rate transport equation –Model remains consistent with logarithmic velocity profile for –No new closure constants are introduced into model

Coupling GEM/LAM with urbanSTREAM (One-Way Interaction) GEM/LAM domain urbanSTREAM domain

Inflow Condition from GEM/LAM

Comparison with Experimental Data Location 1 Location 2

Mean wind speed and direction at Location 1 Expt data Drag force

Mean wind speed and direction at Location 2 Expt data Drag force

Coupling GEM/LAM with urbanSTREAM Mean velocity profile: Below canopy height (exponential profile) Above canopy height (surface layer profile with diabatic correction) Above surface layer (constant wind profile) Diabatic corrections: Unstable Stable Blend profiles at canopy top:Below canopy

Coupling GEM/LAM with urbanSTREAM Mean velocity profile: Blend profiles at canopy top:Above canopy need to shift surface-layer profile upwards by d, the displacement height of canopy U s is velocity at top of surface layer Estimate of height to top of surface layer: Input: roughness length of canopy displacement height of canopy boundary-layer height Monin-Obukhov length reference velocity above canopy Determination of U s from reference velocity if reference height Parameterization for d : attenuation coefficient Parameterization for frontal area density

Coupling GEM/LAM with urbanSTREAM Turbulence kinetic energy profile: (Simplified) Below canopy where Above canopy where need to know value of TKE at some reference height above canopy, then

Coupling GEM/LAM with urbanSTREAM Turbulence kinetic energy profile: (Second-order closure model) Above canopy Below canopy where NB: Skin frictioncan be obtained from mean velocity profile, since at canopy top

Coupling GEM/LAM with urbanSTREAM Viscous dissipation profile: Length scale determined as Imposed limiting length scale restricting depth of inertial sublayer above canopy

Interfacing urbanSTREAM With Urban Dispersion Models urbanPOST takes output from urbanSTREAM and writes out flow statistics required by various urban dispersion programs Coordinate system used in urbanSTREAM (meteorological convention): x W-E (index = i ) y (index = j ) S-N z (index = k ) Vertical Numbering convention : (direction l) - grid lines (l = 1, 2, …, NL-1) - cell centers (l = 2, 3, … NL-1) [interior] l = i, j, k … l =123 NL-1NL-2 l =12 3NL-1 NL l

urbanSTREAM to urban(A)EU or urban(B)LS-0 urbanSTREAM urban(A)EU urban(B)LS-0 File: urbanEU_input.dat (dt > 0)

urbanSTREAM to urban(B)LS-1 urbanSTREAM urban(B)LS-1 File: urbanLS_input.dat

grid_generator Summary urbanSTREAM(-P) urbanPOST urban(A)EU urban(B)LS-0 urban(B)LS-1 ArcView Shape file (*.shp,*.dbf) Meteorological data file (urbanGEM / LAM) grid generation flow solver post processor AVERAGE.dat GridInfo.dat urban dispersion  Eulerian  Lagrangian urbanLS_input.dat urbanEU_input.dat input.par boundary_interpolate interpolate BCs urbanGRID gridded output individual receptor locations