UWERN microscale model: discussion of development of a cfd code to examine airflow in urban enivironments

UWERN microscale model: discussion of development of a cfd code to examine airflow in urban environments.

OBJECTIVE and SUMMARY:

To discuss whether there is an interest and a need to to develop a building scale code that could

act as a stand alone cfd model code which is a gratis UK code?

act, and feedback with a micro-scale / boundary layer code of the lower atmosphere, again as a UK developed resource?

Is there an interest and demand in the community to develop this facility?

Responses are requested to the email group generated at the 1^st microscale modelling workshop as to

questions (a) and (b) above,

comments or changes to the scientific methodology suggested below,

if sufficient interest is generated, would you be willing to participate in a short half day meeting to see if this or a similar project should be taken forward.

Background
Project aim:

The aim is to resolve physical and dynamical scales down to a few metres, and enable resolution of flow over steep terrain and other atmospheric high-resolution processes in the atmosphere. To this aim a workshop was organised in Spring 2003, and recommendations produced. This document is a consequence of discussions following the workshop.

Workshop conclusions:

Many recommendations were made and these are listed on the web page:- http://www.env.leeds.ac.uk/~alan/microscale/workshop1/workshop1summary.html

It was decided that an "urban scale, cfd type" and "steep terrain" models were not compatible. In principle it was agreed that it would be most appropriate to develop the New Dynamics Unified Model, or similar, and that a terrain following code could, in principle, with suitable modification, handle steep slopes, but not buildings. Thus if building scale problems were to be addressed, then separate models would need to be constructed.

After discussions with the Met Office (letter, 23^rd May 2003), there is a feasible, if ambitious work plan, which will produce a research microscale model suitable for flow over steep terrain and for use as a Cloud Resolving Model.

Thus a decision as to whether there is interest in developing an urban code is now appropriate.

Urban Code

At the workshop, questions were raised.

Cfd codes. How could use of suitable existing codes or approaches would be assessed.
How much resource is required? Should a new code be created for a non-adaptive / structured / unstructured finite volume approach?
Can a "cfd type model" be applied or developed using the UM or similar equation set.
Should an unstructured model be utilised?
How could such a project be achieved?

Names for those interested in an urban scale model include S. Belcher, A. Blyth, R. Britter, X. Cai, I. Castro, B. Dawes, A. Gadian and A. Robins. There are others interested for the creation of a new cfd code include C. Greenhough, Head of numerical techniques at RAL , and M. Hubbard, Computation, Leeds, but this is now probably beyond the scope of the project.

Proposal.

I propose that interested parties should be circulated to initially discuss this by email. If sufficient interest is forthcoming, to have a short meeting to propose a research project.

Essential requirements.

The UM equation set, or an equation set consistent with the microscale model should be used as basis of the model. Initially, dry code should be implemented, with the use of thermal forcing and larger scale initialisation possible. The ability to create a 3d mesh (2-d solutions initially) is required. The ability to follow tracers is essential.

Details.

To act as a starting point, I am proposing the following content:

A dry cfd code, but including water vapour, inert tracers and thermal forcing, should be applied to field data (e.g. DAPPLE project). Available existing cfd codes should be used. This "surface" model would act as the lower boundary conditions be interfaced with a microscale model. The aim of the project would be to model and identify the pollutant transfer to and from the surface layer to the atmospheric boundary layer, to examine the mixing processes between the two layers. The "unsteadiness" of the boundary layer wind and stability structure will impact on the ventilation of the "surface layer" and the proposal would identify these exchange processes. This work could be carried out by perhaps two p-g students, one working on the cfd code and the other developing the microscale code. If successful, the long term goal would be to produce a combined model.

There are alternative modelling strategies. E.g. Develop a new finite volume code., and these need to be discussed.

Timing

If following the email discussion, there is suffiecient interest, then a meeting during the 1^st week of October ??? be arranged. Possible agenda structure would include

Is an urban scale meteorological model necessary.
If so what are the scientific objectives?
Is it useful to propose a UWERN project?
What is the project?
Who wants to be involved and what contribution could be made?
Do we need any resource?

Summary

What is the interest and viability of developing a project to look at the mixing processes between the surface urban layer and the free atmospheric boundary layer above.

Comments please?