The atmospheric boundary layer wind tunnel is a purpose-built facility designed specifically to simulate flow fields associated with atmospheric winds.

The 15m upstream fetch makes it possible to generate the turbulence and shear characteristics essential for accurate simulation of the Earth’s atmospheric boundary layer.

Key facts

  • 2.4 x 1.2m (8’x4’) working section.
  • 15m flow development section.
  • Closed working section open return circuit.
  • 0.5m/s to 16m/s flow speed.
  • Interchangeable turbulence grids and surface roughness elements.
  • Computer controlled three axis over-head traverse system.
  • Floor mounted 360˚ rotating turntable.
  • Six component dynamic force/moment balance.
  • Multi-port simultaneous pressure scanning system.
  • Four channel hot wire anemometer.
  • High speed particle image velocimetry.
  • Multiple smoke filament flow seeding.
  • Hydrocarbon analyser for plume dispersion studies.

Summary of applications

Pedestrian wind environment: Adverse pedestrian-level wind conditions can seriously affect the usability and desirability of a facility or location. Scale model testing provides designers with information regarding potentially uncomfortable or dangerous wind conditions. Assessment of key issues allows the designer to optimise the proposed site early in the construction process thus minimising costly remedial work.

Wind loading on buildings and structures: The wind tunnel can be utilised to obtain wind loading data from mean and fluctuating wind forces and moments on structures. Cranfield is fully equipped with high accuracy measurement tools such as synchronous pressure measurement systems, hotwire anemometry and high frequency force/moment balances.

Dispersion tools: Smoke flow visualisation can be utilised to identify the dispersion patterns of pollutants exhausted from stacks or buildings. Coupled with the FID tracer system, this can be used not only to identify areas of excessive concentration of harmful or nuisance substances but also to provide design data to optimise inlets and exhausts. Smoke can also be used as a flow visualisation tool to assess the performance of natural or mechanical ventilation systems.

Further facilities: The wind tunnel is flexible in construction allowing it to be configured to specific test conditions and apparatus. The wind tunnel offers a secure rigging and tunnel control room and the University also benefits from an experienced model manufacturing workshop.

Using the facility

Applications include:

  • Airflow characteristics around buildings and structures, including pedestrian environment, helicopter landing areas (CAP437) and natural ventilation (BS 5925);
  • Surface pressure measurements taken for wind loading for buildings (BS 6399-2), building heating, ventilation and air conditioning testing (HVAC), and gas turbine intakes;
  • Static and dynamic wind loading of tall structures, lattice towers (BS 8100-1), chimneys (BS 4076) and bridge structures (BS 5400).