Engineered solutions to Jet Blast, Propeller Wash and Rotor Wash

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

During landing, take-off, taxiing, and engine testing, aircraft engines generate rapidly moving air known as jet blast, propeller wash, and rotor wash. For large jet aircraft, this jet wash can result in air speeds measuring hundreds of kilometres per hour. If not properly controlled, it can pose a significant risk to pedestrians, staff, vehicles or buildings on or near airports. For example, it can knock over people, flip cars, and damage anothaircraft. To address this risk, the Manual of Standards for Airports, Section 6, imposes limits on jet blast, propeller wash, and rotor wash velocities in areas where people or equipment are likely to be present.

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 solutions typically involve a jet blast deflector (JBD) placed between the runway or helipad and affected locations. These deflectors may be manufactured or earthen and are also referred to as blast fences, shields or walls.

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. Case specific optimisation of the blast fence can reduce the extent of this recirculation region without compromising the system performance.

Careful placement of control measures is necessary to ensure maximum performance and value, while also avoiding significant collision risks and any impact on the airport anemometer’s wind speed. Computational Fluid Dynamics (CFD) modeling can assess a range of barrier types, sizes, and locations to quickly identify the most appropriate solution for your airport.

Related articles: Predicting and controlling helicopter rotor wash

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