Unsteady Aerodynamics of Wings in Extreme Conditions

Currently aircraft designers must design for the worst case scenario plus a safety factor. This worst case scenario is always at the edge of the performance envelope and is associated with extreme manoeuvres and /or gusts. The aerodynamic flow over thse cases is characterised by highly unsteady, separated flow regions and possibly vortical interactions. Despite the importance of these extreme cases in dictating the aircraft structure very little is known about these highly separated flows and the current theoretical models are poor at predicting the unsteady forces.

The aim of this project is to achieve a complete understanding of the unsteady aerodynamic behaviour of generic wings in extreme conditions involving plunging motion near the stall angle. This improved knowledge of the vortical flows, and their influence on aerodynamic force generation, will be used to develop accurate reduced-order models, to improve the accuracy of numerical simulations and to develop effective high-frequency load control strategies. The proposed project will address these aspects through a combined experimental (University of Bath) and computational (University of Southampton) approach using state of the art facilities.

The benefits of this increased understanding of the highly separated flows, accurate reduced-order models and accurate numerical simulations will aid aircraft designers by removing some of the uncertainty that surrounds flight at the limits of the performance envelope. In addition, the high-frequency loads control strategies are a potentially feasible method of then controlling and limiting these extreme loads. Hence, the aircraft design can not only predict with greater accuracy but also control. Both elements will allow for lighter, more fuel efficient aircraft.

Economic: The ability of improved reduced-order models and improved numerical simulations to predict the unsteady loads over an aircraft in extreme condition with greater confidence will allow aircraft manufacturers to design lighter more fuel efficient aircraft. In addition high-frequency loads control is to be investigated as a possible new technology for aircraft. The concept is that control of the loads at the first point of contact, the fluid-structure interface, will allow for the peak loads to be maintained within more acceptable bounds. For aircraft this would improve ride quality and expand the design envelope enabling weight savings across the entire aircraft structure. This in turn would equate to cost savings, both in manufacture and use, resulting in a cheaper aircraft to build and fly. In addition improved aircraft efficiency equates to decreased fuel consumption helping the aircraft industry meet its environmental targets. The aerospace sector is represented in this current proposal by Airbus UK, although we have also described in the Pathways to Impact routes to wider dissemination. In addition these loads control technologies are potentially viable for the wind energy sector. For wind turbines effective loads control would yield savings both directly (reduced extreme forces on the blades mean reduced forces on all components), and indirectly (reduced extreme forces allow lighter blades which reduces fatigue on all power train and tower components allowing for lighter, cheaper components), which would lead to cheaper renewable energy.

Scientific: The scientific impact consists of five components: (i) new reduced-order models that can predict unsteady forces in highly separated conditions (ii) new insight into unsteady vortical flows and how they relate to the unsteady forces (iii) a new hybrid LES model that will predict the unsteady flow over a plunging wing in a computationally efficient manner, (iv) detailed experimental and computational unsteady results perfectly suited to CFD validation and (v) new loads control strategies a detailed investigation of their application in a highly three-dimensional unsteady environment with the associated control models.

People: Both of the PDRAs will directly benefit from the opportunity of being involved in an interesting and novel collaborative project with great potential for impact and publications. In particular they will get to work alongside our collaborative partner, Airbus UK, and will both have the opportunity to undertake a two month secondment. For the experimental PDRA this is so that they can develop the reduced-order models in partnership with the user; for the computational PDRA this is so that they can disseminated the new numerical methods and understanding developed during the project. The industrial experience and contacts will be very useful in their future careers.

Further: The wind tunnel rig and loads control wing developed as part of this proposal will be permanent artefacts that have further research possibilities beyond the scope of the current proposal. There is therefore the possibility of further grants and research, with associated impact.