Numerical Simulations of High Resolution Urban Flow Using the RAMS Model

Transcription

1 Numerical Simulations of High Resolution Urban Flow Using the RAMS Model Tamir Reisin, Soreq NRC, Israel Orita Altaratz-Stollar, Department of Environmental Sciences, Weizmann Institute, Israel Silvia Trini Castelli, ISAC, C.N.R., Torino, Italy

2 Numerical Simulations of High Resolution Urban Flow Using the berams Model Tamir Reisin, Soreq NRC, Israel Orita Altaratz-Stollar, Department of Environmental Sciences, Weizmann Institute, Israel Silvia Trini Castelli, ISAC, C.N.R., Torino, Italy

3 Outline Background Model Setup Flow Results Dispersion Results Summary and Future Plans Ubatuba, Brasil 3

4 Aim: To describe pollutants dispersion in an urban environment. Especially, tracking and predicting the atmospheric dispersion of hazardous material releases to the atmosphere. Methodology: To apply a high resolution (~1m) atmospheric model to describe the flow in canyon streets and around buildings. Ubatuba, Brasil 4

5 Tel Aviv Univ. 1) Weather prediction system (MM5) 2) Mineral dust prediction (ETA) Verification Extending the pollution inventories Initial and boundary conditions Hebrew Univ. Jerusalem High-resolution transport and photochemical models (RAMS, TDM, CAMx, Emission Inventory) Initial conditions TECHNION, CNR ROME Measurements of physical and chemical properties of particles, including heavy metals and dust Validation Local effects, dispersion time, hotspots locations SOREQ Urban air flow model (RAMS) Ubatuba, Brasil 5

6 Atmospheric Model vs CFD Interface with larger scale meteorological models: initial conditions, boundary conditions, data assimilation. Soil model and land use parameterizations. Parameterizations of precipitation, scavenging, solar radiation, etc. Time dependent solutions. Ubatuba, Brasil 6

7 CFD vs Atmospheric Model Robust numerical schemes for high resolutions. Turbulence parameterizations on buildings scales. Wall boundary conditions. Complex grid geometries. Steady state solutions. Ubatuba, Brasil 7

8 The RAMS model and urban flow Adaptive Aperture vertical coordinate system. Steep topography explicit definitions of buildings. RAMS recognizes walls numerically but not physically. Therefore, the first step in this project is to improve RAMS treatment of buildings and walls, specifically: Turbulence parameterization. Boundary conditions on walls. Ubatuba, Brasil 8

9 Model Setup Igud Arim Ashdod Building. Resolution of O~(m). Domain Size: x-250m, y-180m, z-60m. Time step: ~0.01s Turbulence scheme: RNG k-ε (Following Kim and Baik, AE 2004). Homogeneous base state environment provided by a larger scale RAMS simulation. Ubatuba, Brasil 9

10 Igud Arim Ashdod building Ubatuba, Brasil 10

11 Model Setup The buildings Ubatuba, Brasil 11

12 Model Setup The buildings Ubatuba, Brasil 12

13 Resolving the flow around buildings Three nested grids: 18m, 6m and 2m on the horizontal. Vertical resolution 1m. Results after 3.5 min of simulation. Ubatuba, Brasil 13

14 Horizontal resolution=18m Ubatuba, Brasil 14

15 Horizontal resolution=6m Ubatuba, Brasil 15

16 Horizontal resolution=2m Ubatuba, Brasil 16

17 Horizontal resolution=6m Ubatuba, Brasil 17

18 Horizontal resolution=2m Ubatuba, Brasil 18

19 Ubatuba, Brasil 19 Turbulence Parameterization Turbulence Parameterization RNG k-ε model (Kim & Baik, AE 2004), R k C x K x x U u u k C x U t x k K x x U u u x k U t k j m j j i j i j j j k m j j i j i j j + = + + = + ε ε σ ε ε ε ε σ ε ε ε, )k ( ) / ( C R η + β ε η η = µ η. x U x U x U k / j i i j j i ε η = / 2 1/ + = ε ν ν C µ k K m Additional sink term for nonequilibrium strain rates (0.0845,0,7179,0.7179,1.42,1.68,0.012,4.377) ),,,,,, ( = η β σ σ ε ε ε µ C C C k TKE Energy dissipation rate

20 Wind Vectors k-ε k-ε RNG Ubatuba, Brasil 20

21 TKE k-ε k-ε RNG Ubatuba, Brasil 21

22 k-ε k-ε RNG Ubatuba, Brasil 22

23 k-ε k-ε RNG Ubatuba, Brasil 23

24 k-ε k-ε RNG Ubatuba, Brasil 24

25 k-ε k-ε RNG Ubatuba, Brasil 25

26 Boundary conditions on buildings walls We apply a logarithmic interpolation where ζ 0 is the coordinate at the building face, ζ 1 and ζ 2 the coordinates of respectively the first and the second atmospheric grid points close to the building. u i ( ζ ) = u 1 i ζ 1 log ζ 0 ( ζ 2) ζ 2 log ζ 0 For u, v and w and imposing the no-slip condition ( ζ ) 0 u i 0 = T( ζ 1 ) = T( ζ 2 ζ 1 )log + T ζ0 ζ 2 log ζ0 build ζ log ζ 2 1 For temperature, T build is the wall s temperature. Ubatuba, Brasil 26

27 Air temperature differences for buildings walls at 20C and 5C. Results after 5 min of simulation. Ubatuba, Brasil 27

28 T build =5C Ubatuba, Brasil 28

29 T build =5C Ubatuba, Brasil 29

30 T build =20C Ubatuba, Brasil 30

31 T build =20C Ubatuba, Brasil 31

32 T build =5C T build =20C Ubatuba, Brasil 32

33 T build =5C T build =20C Ubatuba, Brasil 33

34 T build =5C T build =20C Ubatuba, Brasil 34

35 T build =5C T build =20C Ubatuba, Brasil 35

36 T build =5C T build =20C Ubatuba, Brasil 36

37 T build =5C T build =20C Ubatuba, Brasil 37

38 Summary RAMS6 was used to simulate the flow around the Igud Arim Ashdod building. Turbulence parameterization and boundary conditions on walls were modified. The RAMS model seems to be appropriate to simulate the atmospheric flow in a simplified urban environment. The high spatial resolution (1-2 m) that can be implemented in RAMS permits resolution of the wind flow that develops in the close vicinity of the buildings. Ubatuba, Brasil 38

39 Summary (cont.) The atmospheric flow that develops is very complicated and very sensitive to the ambient wind speed and direction as well as to the temperature profile. The flow pattern around the buildings is significantly influenced by the buildings walls temperature. The HYPACT model was implemented to simulate the dispersion of tracers. Ubatuba, Brasil 39

40 Future Plans Improvement of boundary conditions (fluxes). Comparisons with measurements/cfd models. Integration into a modeling system for urban pollution (resolutions cascade). Urban simulations with complex geometries using OLAM (because of its gridding capabilities). Ubatuba, Brasil 40