Transonic buffet
Transonic buffet refers to shock oscillations in transonic flow over a rigid stationary wing. These oscillations are caused due to shock induced boundary layer separation. The significant parameters that influence buffet onset are Mach number and angle of attack beside the airfoil shape. One mechanism that is popular in explaining the cause of transonic shock buffet is that pressure waves propagate from the foot of the shock towards the trailing edge from where acoustic waves are reflected back towards the shock. This feedback loop is said to be the engine to drive the shock oscillations on the suction side of the wing.
We are investigating the influence of angle of attack (AOA), finite span, flexibility and wing inertia, and the interaction of transonic buffet with flutter using URANS simulations on the Benchmark Supercritical Wing (BSCW). BSCW is a finite span, uniform, unswept wing of aspect ratio 2 and a NASA second generation supercritical wing-section SC(2)-0414.
At a given Mach number and Reynolds number, for given wing or wing-section, the angle of attack is a critical parameter. Transonic buffet initiates at a buffet onset AOA and progresses to a fully developed buffet flow. However, above a certain AOA known as the buffet offset AOA, buffet ceases to exist. The boundary layer is fully separated and there are no shock oscillations, just a stationary shock.
BSCW, M = 0.85, Re = 4 million, SA turbulence model. Buffet onset occurs below 0 deg AOA. As AOA increases, the mean lift coefficient increases. Between 5 and 7 deg AOA, shock oscillations, or buffet, ceases and buffet offset sets-in.
BSCW, M = 0.85, Re = 4 million, SA turbulence model. RMS coefficient of pressure distribution on suction and pressure surfaces clearly shown unsteadiness or shock buffet on both the surfaces at all 0-5 deg AOA simulated. Shock oscillations on both surfaces is known as Type 1 shock buffet.
Magan Singh and Kartik Venkatraman (2023). The influence of angle of attack on the nature of transonic shock buffet in a finite span wing. In: 57th 3AF International Conference (AERO2023), Bordeaux, France, March 29-31, 2023.
Streamlines
Streamlines on the suction surface of a finite span wing showing the span-wise flow from wing tip to root. Flow is strongly 3D.
M = 0.85, Re = 4 million, AOA = 5 deg, SA turbulence model.
Skin friction lines
Skin friction lines on the suction surface clearly showing flow separation from almost 80% span.
Schlieren
Numerical schlieren or density gradient magnitude at the 60% span station clearly showing the shock and flow separation over the suction and pressure surfaces. Shock amplitude is approximately 6% of chord.
Magan Singh, Tumkur Pradeepa Karnick and Kartik Venkatraman (2022). Transonic buffet and buffeting in the finite span Benchmark Supercritical Wing (BSCW) in 2022 AIAA Aviation Forum, Chicago, IL, June 27 - July 1, 2022. https://doi.org/10.2514/6.2022-4172.
2D Transonic shock buffet
Transonic shock buffet over a NASA SC(2)-0414 supercritical airfoil. M = 0.75, Re = 4 million, AOA = 5 deg. SA turbulence model with Edwards-Chandra and compressibility corrections.
Divergence of velocity snapshots over a time period of oscillation.
Arif Md, Magan Singh, Tumkur Pradeepa Karnick and Kartik Venkatraman (2023). Two-dimensional transonic buffet in a supercritical wing section. In: 2023 AIAA SciTech Forum, National Harbor, MD, USA, January 23-27, 2023. https://doi.org/10.2514/6.2023-1567.
Md Arif, 2022. Numerical investigation of transonic buffet over a supercritical airfoil. MTech thesis. Department of Aerospace Engineering, IISc.