A probabilistic framework for assessing helicopter landing conditions within the ship air-wake

Abstract

Particle Image Velocimetry (PIV) measurements were performed in a wind-wave facility to characterise the ship air-wake on the landing deck (LD) of a stationary NATO-GD model. To our knowledge, this is the first laboratory ship air-wake experiment in a naturally-developed boundary layer over a water surface. This study builds on our previous wind tunnel tests over a solid floor (Setiawan et al. 2022, Ocean Engineering, vol. 260, 111931). The results indicate that the air-wake statistical characteristics are comparable to the wind tunnel data, with the mean flow and turbulence kinetic energy only differing by 5% and 2%, respectively, from the flat-plate baseline flow. We further developed a new probabilistic method to estimate the “landing risk” percentage based on the likelihood of extreme turbulence events. Although the exercise was performed using the local vertical wind fluctuations ${〈{\sigma }_{wn}〉}_{LD}$ employing a threshold specified for civil aviation, the approach can be adapted for other metrics or can employ a more suitable limit for the Navy context. In essence, we mapped the fractional time (out of the total PIV snapshots) when the ${〈{\sigma }_{wn}〉}_{LD}$ exceeded the selected threshold. Having shown Reynolds number independence, we scaled up the velocity data in order to emulate a set of higher reference velocities. It is shown there is a non-linear increase in the “landing risk” percentage with increasing reference velocity (wind speed), and the various inflow conditions affect landing risk.