Shock Buffet and Associated Fluid–Structure Interactions of the Benchmark Supercritical Wing

Abstract

This study focuses on the fluid–structure interactions of the Benchmark Supercritical Wing (BSCW) at buffet conditions (transonic flows and moderate angles of attack). It presents unsteady Reynolds-averaged Navier–Stokes simulations of the fixed BSCW, the BSCW undergoing prescribed pitch motion, and the BSCW suspended on springs in one and two degrees of freedom. The study’s objectives are to 1) establish the BSCW buffet properties and 2) investigate the aeroelastic and prescribed-motion responses of the wing at buffet conditions. The results indicate that the BSCW buffet is predominantly two-dimensional in terms of its characteristics, although it is greatly affected by the tip flow. The response to prescribed pitch motion and the aeroelastic response of the spring-suspended wing display similar phenomena, where the response in the buffet frequency is suppressed once the oscillation amplitude exceeds some threshold, and the structural and aerodynamic responses are solely at the structural frequency. At the studied conditions, the BSCW undergoes stall flutter, dominated by pitch oscillations, compared to a bending-torsion coalescence flutter at lower angles of attack. We conclude that the shock buffet does not drive the BSCW flutter instability. However, both the buffet and stall flutter develop at similar flow conditions of detached boundary layer behind a strong shock at transonic Mach numbers and moderate angles of attack.

Towards extending the aircraft flight envelope by mitigating transonic airfoil buffet

“…Finally, we like to point out that the present study focuses on the aerodynamics of 2D transonic airfoil buffet and neglects aeroelasticity as well as 3D effects occurring on realistic swept wings where the nature of the buffet phenomenon can be additionally influenced by interactions with, e.g., the engine nacelle 75 and the aircraft fuselage 76 . However, the dominant aerodynamic phenomena of 3D straight and mildly swept wings are similar to 2D airfoil buffet 12 , 77 , 78 . Therefore, the present findings provide a good indication of the behavior of the complex real-world system and thus, a valuable basis for more sophisticated prospective investigations, which certainly have to be conducted prior to approaching real-world aircraft implementations.…”

“…The present study reveals a second benefit of PTEs - their ability to attenuate self-sustained shock wave oscillations associated with the transonic buffet phenomenon. Several recent studies observed a direct connection between this aerodynamic instability and a particular class of transonic aeroelastic stability problems 9 – 12 (a review of recent literature is provided in the Supplementary Information, section 3) , which constitute a hazard to flight safety due to their undesirable impact on the flight control system and the structural integrity. Therefore, the present findings are important for the aviation sector in outlining a promising strategy to mitigate certain safety-critical aerodynamic and aeroelastic instabilities.…”

“…However, non-classical flutter occurring in transonic flows has different instability characteristics that also depend on the Mach number, i.e., the non-dimensional ratio of the local flow velocity to the local speed of sound, and the angle of attack, which refers to the angle between the freestream velocity and the inclination of the airfoil. Recent research has shown that transonic aeroelastic problems arise when the flow is close to or in an unsteady state 9 – 12 (for an extended literature review, the interested reader is referred to the Supplementary Information, section 3) . This aerodynamic instability is called transonic buffet and describes self-sustained shock wave oscillations occurring on the aircraft wings 13 – 16 .…”

“…Overall, the findings presented in this contribution clearly demonstrate the ability of porous trailing edges to mitigate transonic airfoil buffet. Since one class of transonic aeroelastic instabilities of the wing structure is connected to the flow field unsteadiness associated with buffet 5 , 9 , 10 , 12 , the aerodynamic stabilization is expected to positively impact the structural behavior for particular flow conditions. Thus, due to their benefits compared to other buffet control technologies, porous trailing edges possess great potential in advancing civil aviation by prospectively extending the limits of the flight envelope in the high-speed regime.…”