Urban Scale
Weather Modeling
NCAS and CD-adapco Partnership
Fred Mendonça, CD-adapco
Just before his retirement in April 2006, NCAS
director of weather research,
Professor Paul Mason, and CD-adapco’s President, Steve MacDonald,
agreed
exclusive Partnership terms, which will lead to an urban scale weather
modeling code. The prediction methodology, using the UK Met Office’s
operational Universal Modeling code to drive localized STAR-CD models
at
building and street-level scales, is aimed eventually at 5-day forecasting
of
urban air quality, dispersion and heat transfer.
∇ Fig1: Ariel photograph of Marylebone in London (Google Earth image)
∇ Fig2: Polyhedral mesh at ground level
A detailed assessment of three major commercial CFD codes has led to indications that proper use of Large Eddy Simulation (LES) capabilities leads to essentially identical results from all three codes and is a feasible approach. NCAS teams, initially at the Universities of Southampton and Reading led by Professors Ian Castro and Stephen Belcher, respectively, will concentrate in the next phases on further exploitation of CD-adapco’s advanced modeling techniques, centered around the recently released STAR-CD version 4.0.
Professor Castro, who with Dr Zhengtong Xie led the
evaluation of commercial software at Southampton notes, “Partly for technical reasons but also because they have been
the most engaged in the collaboration, CD-adapco has been
identified as the vendor most appropriate for NCAS’s needs”.
Then referring to CD-adapco’s own ParaSolids based
geometry modeler and CAD integrated product, he adds that, “STAR-Design
is very user-friendly for complex geometries, generating polyhedral meshes
which we consider essential for general urban topologies”. Professor
Belcher said, “There is
a growing need to be able to simulate flows in urban areas for
applications ranging from pedestrian comfort and wind
loading of buildings to dispersion of traffic pollutants and
terrorist releases. This new partnership promises the tools we
need to tackle these issues.” Fred Mendonça, CD-adapco’s
director of Vertical Applications and Expert Systems adds, “We
are particularly pleased with NCAS’s decision and look forward
to productive collaborations. Urban Weather Modeling
continues to be an area of keen interest to many research
groups, environmental agencies and building services organizations
worldwide; our commitment to this partnership
confirmsour serious intentions towards environmental flow
predictions”.
Dr Xie has produced a set of demonstration predictions using STAR-CD v4.0. Results to date point clearly at the viability of LES with polyhedra for building applications, validated against experimental measurements and the University’s own DNS code, used by Dr Glyn Thomas (its originator) and Dr Omduth Coceal (at Reading) to produce genuine DNS data for similar situations. The first predictions were performed on laboratory models comprising simple box-shaped buildings. Results pointed clearly to the viability of polyhedral meshes for building environmental flows. CD-adapco software has now been applied to more complicated models – for example London’s Marylebone district - see the Google Earth image and a view of the polyhedral mesh at ground level in Figure 2. Mean flow and turbulence statistics, agree well with wind tunnel data obtained using a 1:200 scale model of the region shown in Figure 2.
In the next phases of the work, NCAS teams at the Universities of Southampton and Reading will concentrate on exploiting CD-adapco’s modeling tools, centered around the recently released STAR-CD version 4.0, linking it with the UK Met Office’s codes and exploring the issues that arise in scalar (pollutant) dispersion and heat transfer effects. Licensing arrangements between CD-adapco and NCAS – free for all approved NCAS PI’s working on urban meteorology under the Weather Directorate – were finally approved by all parties in August 2006. Further information is available from Professor Ian Castro at the University of Southampton.