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Miskam basicsMISKAM – Mikroskaliges Strömung-und Ausbreitungsmodell (Microscale flow and dispersion model)Developer: Dr. J. Eichhorn, Universität Mainz (1989)

Custom software:• Urban ventilation & pollutant dispersion• Meet VDI Richtlinie 3783 Blatt 9 german standard• Validated numerical model

Model setup:• RANS- equation: with k-ϵ turbulence model closure• Dispersion equation : passive scalar transport One-way coupling

Numerical gridOnly hexahedral, structured meshmax. 5 millions grid cellsRectangular block-structures

• buildings, vegetation , bridges/passages

Boundaries• Inlet: 1D logarithmic velocity profile• Upper boundary: Airflow parallel to the surface• Lateral boundaries: No normal velocity component

Perspective view of an urban districtSource: Marton Balczó

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Miskam basicsPollutant emission modellingPoint source (mg/s)Area source (mg/m2/s)Line source (mg/m/s)

Differentiated by x y directions

Miskam 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: Márton Balczó,

Gas exhaust stack of István Benkő elementary school in Újpest

Urban ventillation of city centre Millenium

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Extent of computational domain• All the airflow structures developing around the buildings

(e.g. wakes, vortices etc.)

• „5L rule”

• Dmin= Lb+4wm • L =size of the smaller edge of the building• w = magnitude of wind velocity• The height of the domain > 3H of the tallest building

Numerical grid quality requirementsThe applied numerical schemes to work accurately:• Smoothness: max. 1.2 growth rate• Aspect ratio: max. 1:2• Skewness:

-> max. 0.85 for hexa elements (Miskam automatically fulfils this requirements)

Guideline for numerical modeling

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Start the program: Start menu / WinMiskam.exe

Step 1: Mesh generation

Step 2: Fit the layout map Load map:http://www.ara.bme.hu/oktatas/tantargy/NEPTUN/ BMEGEATMW08/2012-2013-I Make coordinate mapping

Pixels -> layout Coordinates -> grid

Miskam tutorial

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Step 3. : Digitize the buildings Digitize/edit building Outline the buildings by polygons Mapping of buildings on the grid Stop the edit process!

Step 4.: Allocate the line source Digitize/edit road net CPM10 = 1 mg/m/s (C24h limit = 50 μg/m3) Mapping of road net on the grid Stop the edit process!

Miskam tutorial

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Miskam tutorial

Save your mesh as campus.inp!

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Step 5.: Wind field setup

Running the flow simulation Allocate the target directories Run Miskam in single mode

Step 6. : Concentration field setup

Running the dispersion simulation

Step 7. : Post-processing Wind velocity and concentration data

(read *.zwu \*.zwk files) Horizontal and vertical slices

Pespective view of the domain ( read the *.inp file)

Miskam tutorial

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Thank you for your attention!