Miskam basics

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Miskam basics. Perspective view of an urban district Source : Marton Balczó. MISKAM – Mikroskaliges Strömung-und Ausbreitungsmodell ( M i c ro scale flow and dispersion model ) Developer : Dr. J. Eichhorn , Universit ät Mainz ( 1989 ) Custom software : - PowerPoint PPT Presentation

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Miskam basicsMISKAM Mikroskaliges Strmung-und Ausbreitungsmodell (Microscale flow and dispersion model)Developer: Dr. J. Eichhorn, Universitt Mainz (1989)Custom software:Urban ventilation & pollutant dispersionMeet VDI Richtlinie 3783 Blatt 9 german standardValidated numerical modelModel setup:RANS- equation: with k- turbulence model closureDispersion equation : passive scalar transport One-way coupling Numerical gridOnly hexahedral, structured meshmax. 5 millions grid cellsRectangular block-structuresbuildings, vegetation , bridges/passagesBoundariesInlet: 1D logarithmic velocity profileUpper boundary: Airflow parallel to the surfaceLateral boundaries: No normal velocity component

Perspective view of an urban districtSource: Marton Balcz

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It has been developed for modelling urban wind conditions and pollutant dispersion. The developer is Dr. J. Eichorn, who works in the University in Mainz. It was used in wide range by companies, several authorities in Gemany France, since it is validated by wind tunnel and field measurements and meets one of VDI german air quality standards. Briefly about the governing equations: The airflow is described by the RANS equation with k-e turbulence model closure. The dispersion equation is single coupled with the RANS, that is it has no effect on the flow conditions.

The numerical grid contains only hexa elements up to max. 5 millions. The flow obstacles (e.g. buildings, vegetation bridges) are modelled as rectangular block structures. For the inlet boundary condition you need to supply some characteristic data to define an logarithmic velocity profile.

1Miskam basicsPollutant emission modellingPoint source (mg/s)Area source (mg/m2/s)Line source (mg/m/s)Differentiated by x y directionsMiskam benchmarkAdvantages:Easy mesh generationLow CPU demandValidated for neutral atmospheric stratificationDispersion modelling of non-reactive pollutants

Disadvantages:Inaccurate calculation on vertical mixingNo heat transport modelingNo chemical reactionsNo parallel simulationTerrain modelling restricted to flatlandNo validated model for stabil stratificationNo velocity profileNo boundary layer resolution

Modelling urban pollution dispersion by using MISKAM, 2004 Source: Mrton Balcz, Gas exhaust stack of Istvn Benk elementary school in jpestUrban ventillation of city centre Millenium2In the urban environment pollutant emission sources often take place (e.g. smoke stacks, vehicles with combustion engine etc), which are modelled as point, line or area sources. Finally if wed like to evaluate the MISKAM code it can be revealed thatresolve = felbont2

Guideline for numerical modeling3

Firstly we should learn how to make an adequate model. There are some rules of thumb, which are recommended to respect. The 5L rule is an helpful method to establish the proper sizes of the domain.

3Start the program: Start menu / WinMiskam.exe

Step 1: Mesh generation

Step 2: Fit the layout mapLoad map:http://www.ara.bme.hu/oktatas/tantargy/NEPTUN/ BMEGEATMW08/2012-2013-IMake coordinate mapping Pixels -> layout Coordinates -> grid

Miskam tutorial4

You can also determine the percentage of the refinement area.4Step 3. : Digitize the buildingsDigitize/edit buildingOutline the buildings by polygonsMapping of buildings on the gridStop the edit process!

Step 4.: Allocate the line sourceDigitize/edit road netCPM10 = 1 mg/m/s (C24h limit = 50 g/m3)Mapping of road net on the gridStop the edit process!

Miskam tutorial5

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Save your mesh as campus.inp!6Step 5.: Wind field setup

Running the flow simulationAllocate the target directories Run Miskam in single mode

Step 6. : Concentration field setup

Running the dispersion simulation

Step 7. : Post-processingWind velocity and concentration data (read *.zwu \*.zwk files)Horizontal and vertical slicesPespective view of the domain ( read the *.inp file)

Miskam tutorial

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Create a new projectConfiguration file (.inp)7Thank you for your attention!88