Unsteady aerodynamics of wings in extreme conditions

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

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.

Publications

10 25 50
 
Description We have developed techniques to simulate airfoils under gust conditions and are currently preparing papers for publication. Direct numerical simulations (DNS) and modal analysis techniques are applied to investigate the effect of sweep on the transitional separation bubbles forming on the suction side of a NACA-0012 airfoil. Three different sweep angles are considered. An independence principle was found to be a good approximation for configurations with a fixed ratio of thickness to the chord perpendicular to the leading edge, allowing the lift and drag coefficient to be scaled from a zero sweep case. The transitional flow structure changed with sweep angle, with both swept cases showing more coherent large-scale structures. At moderate sweep angle these structures are perpendicular to the free stream direction, whereas at high sweep they are parallel to the leading edge. A good agreement between Fourier analysis of the DNS data and global stability analysis suggests that the changes are due to the emergence of a strongly unstable global mode. The global modes have coupled acoustic and vortical support, suggesting a coupling between trailing edge sound production and shear layer instability. However the swept cases show increasingly broadband rather than tonal noise characteristics. Dynamic mode analysis shows, additionally, the presence of lower frequency non-acoustic modes in the highly swept case that are not present in the unswept case. Additional simulation of heaving airfoils and wings are under way, with confernec papers accepted for presentation and jounrla papers to follow.
Exploitation Route The simulation results have been used to write a joint paper with University of Bath that is not yet published.
Sectors Aerospace, Defence and Marine

URL https://www.sciencedirect.com/science/article/pii/S0045793019300970?via%3Dihub