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This paper presents a comprehensive experimental aeroacoustic investigation of a propeller under turbulence ingestion. Two turbulence-generating passive grids were utilised to quantify the effect of turbulence intensity on the aeroacoustic characteristics of the propeller. A two-component hot-wire anemometry was employed to study the flow field. The flow field results demonstrate a substantial increase of fluctuating velocity components in both axial and radial directions, concentrated at the mid-span of the blade and near the tip, respectively. Energy spectra analysis in the vicinity of the propeller blade shows significantly higher broadband energy levels with multiple haystacking peaks at the harmonics of the blade passage frequency. Far-field noise and load measurement results show that turbulence ingestion has a strong effect on the aerodynamic loading and acoustic response at the blade passage frequency. The directivity of noise radiation at low frequencies shows a significant tonal noise contribution. Meanwhile, broadband noise radiation is more dominant at the higher range of frequency, especially when the propeller is operated with turbulence ingestion and at higher advance ratio settings. The far-field noise results revealed the haystacking trends in the low-frequency domain of the spectra and are most significant for propellers operating in turbulent inflows.

A concept of growing interest in recent years is that of the Flared Folding Wingtip (FFWT), which can be used in-flight to reduce airframe loading due to gust encounters and augment the handling qualities of an aircraft. The performance of an FFWT is affected by the relative angle between the built-in hinge angle and the flow direction. Therefore, a critical question is the behaviour of such a device at a non-zero sideslip angle, where recent studies have shown that a FFWT can collide with the inner wing at sideslip angles within the flight envelope of an aircraft. In this paper the effect of sideslip angle on the stability behaviour of a wing incorporating FFWTs is investigated both experimentally and numerically. It is shown that the response of FFWTs to sideslip varies not only as a function of flare angle, but also with the angle of incidence of the aircraft and the camber or twist of the wingtip itself.

Recent studies have considered the use of flared folding wingtips (FFWTs) to enable higher aspect ratios - reducing overall induced drag - whilst reducing gust loading and meeting airport operational requirements. The majority of these analyses have been conducted using linear assumptions despite the presence of large wingtip deformations. The aim of this work is to assess the effect of geometric nonlinearities introduced by an FFWT on the static and dynamic aeroelastic response of a wing. In this paper, a geometrically exact expression was formulated to describe the change in both the local Angle of Attack (AoA) and sideslip angle across all fold angles. This expression highlighted that the aerodynamic stiffness of an FFWT, and therefore quantities such as the linear flutter speed, are a function of the fold angle and therefore, the attitude of the wing. This effect was then verified using both: a wind tunnel model of a flexible semi-span wing incorporating an Flared FoldingWingtip (FFWT), and a newnumerical modelling technique, utilising MSC Nastran, which linearised the model about the equilibrium position of the wingtip. The results of these experiments show that the geometric nonlinearities introduced due to the large deformations of FFWTs can significantly affect the dynamics of the system, with flutter speeds varying by over 25%, simply by changing the root angle of attack of the model. Furthermore, good agreement was found between the experimental results and numerical predictions.

Recent studies have considered the use of Flared Folding Wingtips (FFWTs) to enable higher aspect ratios - reducing overall induced drag - whilst also reducing gust loading and meeting airport operational requirements. This paper presents the first experimental research into the nonlinear dynamic behaviour of a wing incorporating FFWTs. Wind tunnel tests were conducted at a range of velocities belowand beyond the linear flutter boundary. The experimental findings are compared with results obtained by conducting continuation and bifurcation analyses on a representative low fidelity numerical model. The results show that beyond the linear flutter boundary a stable Limit Cycle Oscillation (LCO) forms which, dependent on the flare angle, is bounded by either geometric or aerodynamic nonlinearities. Also presented is the effect of a wingtip trim tab on the stability boundary of a wing incorporating FFWTs. It is found that the tab angle can significantly alter the stability boundary of the system, indicating that a moveable control surface on a FFWT could be used ’in-flight’ to extend the stability boundary of an aircraft.