Key outcomes

  • Jet blast effects quantified
  • Jet blast deflector designed
  • Risks mitigated
A volume render showing the jet blast behind a B777 with and without a JBD

Figure 1: Jet blast behind a B777. The top image shows the region of high speed air flow without any jet blast controls, and the bottom image shows the effect of a simple, inclined, jet blast deflector. The blast shield dramatically reduces impacts for pedestrians and vehicles.

Jet blast, propeller wash and rotor wash involve rapidly moving air generated by aircraft engines during landing, take-off, taxiing and engine testing. The jet wash for a large jet aircraft can result in air speeds measuring hundreds of kilometres per hour. If not properly controlled it can pose a risk to pedestrians, staff, vehicles or buildings on or near airports. People can be knocked over, cars flipped, and aircraft damaged. Section 6 of the Manual of Standards for Airports places limits on jet blast, propeller wash and rotor wash velocities in regions where people or equipment are likely to be found.

For small aircraft, these effects are often controlled through separation applied by operational controls, however, with larger aircraft, or operations in small spaces, engineered solutions may be necessary to mitigate the effects. These engineered solutions typically involve a manufactured or earth, jet blast deflector (JBD) placed between the runway or helipad and potentially affected locations.

Contours of velocity on a plane through jet engine.

Figure 2: Contours of velocity through the starboard engine, without (top) and with (bottom) a jet blast fence. The blast fence deflects the jet blast up, resulting in a lower speed, recirculation region downwind of the blast fence. Through case specific optimisation of the blast fence, the extent of this recirculation region can be reduced without compromising the system performance.

Control measures should be placed carefully to maximise their performance and value, without significant collision risk, or influencing the wind speed at the airport anemometer. Using Computational Fluid Dynamics (CFD) modelling a range of barrier types, sizes and locations can be assessed to quickly identify the most appropriate solution for a particular airport.

References: https://www.casa.gov.au/search-centre/rules/part-139-casr-aerodromes