1. MISKAM simulation of the Oklahoma City case Márton Balczó COST 732 MC /WG meeting Madrid, December 4, 2008 Budapest University of Technology and Economics (BME) Department of Fluid Mechanics Part I. - Model setup

2. Motivation MISKAM – a model in operation (100 users in Europe) not as sophisticated like e.g. Fluent – simple grid generation, fewer user settings  faster way to the results | no tuning. I am a user, not a model developer Model was already used in high-rise building project The model RANS with k-  turbulence closure, modified as suggested by Kato & Launder (1993) and López (2002) Dispersion : Reynolds averaged advective diffusion equation (passive scalar) Cartesian non-equidistant grid, buildings blocked out of the grid Versions used in the OKC test: 5.02a (official); 6 beta3 (not yet released)

3. Domain Same as in the FLUENT grid of Jörg Franke 5H - inflow, top and lateral 10H – outflow (H max = 152m Chase Tower F9 ) 2460 x 1200 x 912 m (full scale simulation) Orientation: 180.7° || long axis

4. Grid MISKAM: Building accuracy depends on grid resolution Investigated area and close investigation area determined Building input : Rhino 3D model  Background bitmap  building polygons  prjection to grid in WinMISKAM 460 x 480m, 4x4m Outside: growth rate 1.25 284 x 156m, 2x2m At building walls 1m

5. Grid - vertical resolution 1.5m up to the height of 75m, spreading to 5m at 125m and from then growth rate of 1.2 Refinement to 0.5m at ground level and at the top of lower Park Ave buildings (48-52m) to resolve the top separation bubble 246 x 216 x 108 = 5.74 mio.cells (OKC_3.inp)

6. Garages Openings only on one side of buildings (|| x or || y) possible Garages outside of the investigated area or with too small openings not modelled. Less floors due to rough grid, opening area ~ same Floors fully open, wall structural elements like in the wind tunnel were not modelled.

7. Source Canopy could not be modelled Simple volume sources without momentum Size of source region similar to the size and height of the canopy Source geometry in wind tunnel (from the drawing of Bernd Leitl) Sources in MISKAM

8. Boundary conditions Surfaces : z 0 at the ground 0.12m, building walls 0.01m (for the wall functions) Inlet velocity: 8 m/s at 81m height Profile: logarithmic mean flow, k and  generated by the model from equilibrium Lateral and outflow: no-flux, top: constant values from the top of the inlet profile

9. Numerical schemes MISKAM version5.02a6 beta3 Convection terms Momentum equation Upstream Predictor-corrector method suggested by MacCormack (1969) Turbulence equations* Upstream MPDATA algorithm (Smolarkiewicz and Grabowski, 1989) Transport equationMPDATA algorithm Diffusion terms ADI (Alternating Direction Implicit)-method of Douglas and Rachford (1956) Run IDGridDescription OKC_01OKC_3MISKAM 6 beta3 with garages, z 0 = 0.48 OKC_02OKC_3MISKAM 6 beta3 without garages, z 0 = 0.48 OKC_03OKC_3MISKAM 6 beta3 with garages, z 0 = 0.24 OKC_04OKC_2*MISKAM 5.02a with garages, z 0 = 0.48 Simulation runs

10. To be continued…