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Key outcomes:

  • Terrain induced wind shear and turbulence predicted
  • Operational aviation safety risks understood

Since its completion in early 2016, St Helena’s £285,500,000 airport has attracted significant attention. The first flights to the island faced high levels of windshear and turbulence during final approach to the new runway. From May to September 2016, only eight flights landed at the airport due to the hazardous wind conditions. Commercial airline services were delayed until a smaller and more appropriate aircraft was selected. Synergetics used computational fluid dynamics (CFD) to understand the complex nature of the wind environment over St Helena Airport providing insight that will help prevent a reoccurrence of similar problems at other airports located near complex terrain or large buildings. Optimising the location of wind turbines in complex terrain can also benefit from similar studies.

Figure 1: Computational fluid dynamics (CFD) was used to simulate unsteady turbulence and wind shear over St Helena Airport. This video shows dark red highlighting of regions with high turbulence intensity along the northern approach trajectory.

The simulated results show that headwind approaches from the north experience the most severe wind shear effects, with mean wind speed changes of up to 20 knots occurring over a short distance along the approach trajectory. The high wind shear coincides with large turbulent wind speed fluctuations with a standard deviation of up to 6.2 knots.

wind profiles as the wind passes from the ocean over the cliffs of St Helena Island. Strong terrain induced wind effects result in regions of high and low velocity that change rapidly with position.

Figure 2: The wind undergoes a transition marked by slowing, reversing and recirculating at low altitudes as it flows over the steep terrain of the island.

In hindsight, it is evident that the windshear and turbulence hazards at St Helena airport could have been readily predicted by using CFD or wind tunnel testing during the early stages of the project. Such analysis could have assisted with the selection of a more suitable site for the runway and would have given stakeholders a more complete understanding of operational and commercial risks. Many airports, including Amsterdam Airport Schiphol and Hong Kong Airport, have employed this analysis. The International Civil Aviation Organization (ICAO) has published guidelines for identifying and mitigating windshear risks.

The March 2017 issue of Airports International magazine discusses this study in detail.

For further airport examples see our sector page.