A study on the wind forces on low rise building arrays and their application to natural ventilation design methods.

Due to the complicated flow phenomenon in urban
areas, the assessment of wind pressure forces as well as
the rates of natural ventilation for groups of low rise
buildings is complex. As a result, the current design
methods for the prediction of these forces are oversimplified
and lead to inaccurate estimates of wind forces
and ventilation rates in buildings.
A survey of previous studies regarding wind
properties and their influence on pressure forces along with
work related to natural ventilation, wind loading and air
flow round buildings was carried out. The survey revealed
that no general relationship exists which defines the
interaction between the various aspects of flow. This
thesis, therefore, attempts to enhance our knowledge about
the flow around groups of buildings and suggests a means of
quantifying the interaction between building shape, group
geometry, flow properties and the resulting pressure forces.
The present study has been carried out in a
simulated urban terrain atmospheric boundary layer flow.
A series of model scale experiments were performed for
different building shapes. The study starts with the
investigation of the influence of upstream fetch on the
central model drag before going on to the detailed measurements
on various models covering a wide range of building shapes,
group form and plan area density. The detailed measurements
of mean pressure forces on model buildings situated within a
variety of groups of similar form indicated three different
trends in the behaviour of these forces, corresponding to
the three flow regimes known to exist for flow over general
roughness elements. The existence of these flow regimes
was confirmed by velocity profile measurements. A general
correlation between group geometry, flow properties and the
resulting pressure forces has been suggested.
In order to apply the foregoing results to full
scale building arrays, a method has been proposed to yield
the pressure difference across low rise buildings for the
prediction of natural ventilation rates in an urban built
form. This method takes into account the relevant built
form and flow parameters which are ignored in the current
IHVE design guide method (1970), (applicable to high rise
buildings only). The suggested method includes the
prediction of ventilation rates from the openings in the
walls as well as in the roof. Suggestions have also been
made to revise the British Standard Code of Practice for
wind loading to incorporate the trends which have been
found to be different to those currently recommended.