Abstract
The aviation industry recognises its effects on the greenhouse emissions. Innovative solutions are needed to reduce aviation carbon emissions. Mitigation of the increase in loads during aircraft manoeuvres and gust encounters is an area of potential efficiency improvements in civil aviation. During certain manoeuvres it is beneficial for civil transport aircraft to reduce or alleviate aerodynamic loads by concentrating lift inboard to reduce the wing bending moment.Similarly, reducing the excessive loads during gust encounters in the outer section of the wing reduces the wing bending moment. Gust and manoeuvre loads alleviation is achieved by coordinated deflections of the outer ailerons and spoilers. The alleviation of gust and manoeuvre loads allow the reduction in structural weight or an increase in the wingspan improving the aircraft performance.This research is aimed at studying a novel active aerodynamic loads alleviation system which consists of combining upper and lower surface spoilers. The deployment of the upper and lower surface spoiler may further reduce the lift in the outer section of the wing. This thesis will examine the possible improvements in aircraft efficiency by implementing the novel loads alleviation system.
The investigation was conducted in two stages. The first stage aims to study the aerodynamic properties of the combined upper and lower surface spoilers. The second stage studies the alteration in design loads by simulating the novel loads alleviation system in a three dimensional wing.
The studies will model a sealed flap type spoiler. The upper and lower surface spoiler are hinged at the same chord location.
The range of the parameters were selected in line with the current civil aviation specifications. The analysis should offer an understanding of the effects of the lower surface spoiler on loads alleviation and aircraft performance.
The aerodynamic analysis was conducted using the TAU CFD solver. The CFD analysis simulated the flow around the RAE2822 and SC0710 supercritical aerofoils with different spoiler configurations. The aerodynamic and geometrical parameters governing aerofoil-spoiler systems were varied in order to understand their effects on loads alleviation. The Reynolds Number, angle of attack, hinge location and spoiler deflection were varied in the conducted simulations. The conducted CFD simulations showed that the upper surface spoiler, when individually deployed, reduced the lift. However, there might have been an increase in the pitching moment when the upper spoiler is individually deployed. The combined upper and lower surface spoilers further reduced the lift force and decreased the pitching moment. The lower surface spoiler greatly improved the functionality of the upper surface spoiler as a loads alleviation system.
An additional three dimensional aeroelastic analysis was conducted using a transonic wing designed as a medium range civil airplane wing. A steady and an unsteady aeroelastic solver were developed to estimate the wing forces experienced during gust and manoeuvre. The manoeuvre and gust design cases were conducted in accordance with the corresponding regulations enacted by the European Aviation Safety Agency. The aeroelastic solver incorporated a structural and aerodynamic solver as well as an interpolation method.
The vortex lattice method was corrected to model the influence of the spoilers on aerodynamic loads.
The aerodynamic model developed to estimate the force distribution in the chord and span direction was validated. The aeroelastic solver was also validated.
The validation studies showed good agreement of the estimated forces with the validation data.
The steady aeroelastic analysis of the flexible wing showed that during a $2.5g$ pull-up manoeuvre, the lower surface spoiler when operated in combination with the upper surface spoiler reduced the torque and further reduced the bending moment. Deploying the upper and lower surface spoilers at $25^circ$ and $20^circ$ respectively provided the most effective configuration in terms of bending moment reduction.
This combined spoiler configuration offered a minimum reduction of $14%$ in the bending moment and a minimum reduction of $14%$ in the torque.
In comparison, a minimum reduction in the bending moment of $8%$ and an increase in the torque were achieved when the upper surface spoiler was deployed individually.
The influence of the loads alleviation system on gust load was examined by conducting unsteady aeroelastic analysis of the flexible wing.
%6 gust profiles were considered.
The unsteady aeroelastic solver incorporated Newmark Beta as a time integration method.
The structural damping was derived using proportional damping method. An assumed $3%$ of the first and second natural frequency of the structure was used to assemble the damping matrix. The spoilers were operated at a constant frequency.
The lower surface spoiler has increased the efficiency of the upper spoiler as a gust loads alleviation system.
Short gust did not greatly benefited from lift dumping due to spoilers deployment rate.
The bending moment significantly reduced in medium and long gusts.
The torque was reduced in medium gust length. An increase in the torque occurred at long gusts due to undesired structural excitation.
The system is most effective when the increase of the lift due to gust and the degradation of the lift due to the deflecting the combined spoiler system are probational. During gust encounters, an uncompensated reduction or rapid recovery of the lift due to spoilers deployment or retraction may lead to unwanted structural response which may result in an increase in structural loads.
| Date of Award | 25 Jan 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Jonathan E Cooper (Supervisor) & Thomas C S Rendall (Supervisor) |