Pedestrian wind comfort CFD results showing normalised velocity at 1.5 m height in a dense urban environment for planning and wind microclimate assessment.

Benchmarking pedestrian wind comfort using CFD in complex urban environments

Navier is participating in BeStPLW (Benchmark Study on Pedestrian Level Winds), a UK-wide blind benchmarking exercise led by the UK Wind Engineering Society (WES) in collaboration with industry and academia.

The study aims to assess how consistently pedestrian wind comfort is predicted across CFD and wind tunnel methodologies, and to help establish clearer best-practice guidance for wind microclimate assessments in the UK.

Our involvement reflects Navier’s wider capability in atmospheric boundary layer (ABL) modelling, urban airflow, and external flow interaction with the built environment, with direct relevance to:

Pedestrian wind comfort and safety
Urban pollutant dispersion
Data centre heat rejection and recirculation risk
External ventilation and exhaust re-ingestion studies

Background to the BeStPLW benchmark

Pedestrian wind comfort assessments are now a routine requirement for major developments in the UK, particularly in dense urban environments and high-rise schemes. While guidance exists – notably the City of London Wind Microclimate Guidelines – significant variation remains in how studies are executed and interpreted.

To address this, WES initiated BeStPLW, a structured benchmark designed to:

Compare CFD and wind tunnel approaches on a like-for-like basis
Assess variability between practitioners
Evaluate methods used to derive gust wind speeds
Inform future guidance on minimum modelling requirements

The benchmark was formally introduced at the 14th UK Conference on Wind Engineering (Southampton, 2024) and is supported by ERIES funding for the experimental programme.

The case study area

CFD geometry used for a pedestrian wind comfort benchmark study, showing urban massing and simulation domain — **CFD geometry used for a pedestrian wind comfort benchmark study**

The selected benchmark site is located in Manchester, centred on the Deansgate area, and includes:

A mix of high-rise and low-rise buildings
Complex street canyons
Open spaces and transport corridors

This configuration intentionally introduces challenging flow features, including:

Downwash from tall buildings
Corner accelerations
Channelling and funnelling effects
Building-to-building interference

The geometry has been chosen to be representative of real UK urban conditions, making the findings directly applicable to planning-led wind assessments.

A blind study by design

A key feature of BeStPLW is that it is a blind study.

CFD participants submit results before wind tunnel data is released
Wind tunnel results are not yet published
No calibration or tuning to experimental data is possible

This ensures that outcomes genuinely reflect modelling assumptions, numerical practice, and interpretation – not post-hoc adjustment.

At the time of writing, wind tunnel testing has not yet commenced, and validation data is not available.

Navier’s CFD approach

Atmospheric boundary layer modelling

Navier’s simulations replicate the wind tunnel exposure using a fully developed neutral atmospheric boundary layer, with careful attention paid to:

Inlet velocity profile
Turbulence intensity and length scale consistency
Ground roughness representation
Domain extent relative to building height

Comparison of atmospheric boundary layer profiles from wind tunnel measurements and CFD simulation — **Comparison of wind tunnel atmospheric boundary layer inflow profiles and CFD results**

The objective was to maintain streamwise ABL equilibrium while preserving realistic turbulence decay through the domain.

This capability directly underpins our wider work in:

Turbulence modelling and gust representation

A steady-state RANS approach was adopted, consistent with current industry practice for pedestrian wind comfort studies.

While RANS does not resolve transient gusts directly, gust-equivalent wind speeds are derived during post-processing using established statistical formulations.

One of the explicit goals of BeStPLW is to quantify how different gust derivation approaches influence predicted comfort and safety classifications.

Mesh strategy and numerical robustness

CFD mesh for pedestrian wind comfort assessment in a complex urban environment, showing atmospheric boundary layer domain and near-ground refinement. — **Overview of computational mesh**

The computational mesh was designed to balance accuracy and practicality, reflecting constraints commonly faced in planning applications:

Structured refinement at pedestrian level
Gradual vertical expansion through the ABL
Consistent wall-function treatment aligned with roughness specification
Mesh extents exceeding 15H to minimise blockage and inlet influence

The benchmark provides a valuable opportunity to assess how such choices affect results across different practitioners.

Pedestrian-level assessment methodology

Figure: Pedestrian-level velocity probe results at 1.5 m height, animated across wind directions analysed as part of the BeStPLW benchmark.

As part of the benchmark, pedestrian-level wind conditions are evaluated using over 100,000 probe locations at a height of 1.5 m above ground level, representing typical pedestrian exposure. These probe values are extracted consistently across all participating CFD submissions and will be directly compared against corresponding wind tunnel measurements once experimental data becomes available. This high spatial resolution enables a robust, statistically meaningful assessment of local acceleration, sheltering, and comfort classification across the site, rather than reliance on a small number of isolated sampling points.

Why this matters beyond pedestrian comfort

Although BeStPLW is focused on pedestrian wind comfort, the underlying physics are the same as those governing:

Exhaust re-ingestion around data centres
Pollutant dispersion in dense urban areas
Wind-driven ventilation performance
External plant derating and recirculation risk

Participation in this benchmark strengthens Navier’s ability to defend CFD methodologies in regulatory and peer-review contexts, particularly where wind tunnel testing is not feasible.

Related services

Planning a pedestrian wind comfort study, atmospheric flow assessment, or external airflow analysis in a complex urban environment? Speak with our CFD team to discuss your project.

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