Leading-edge flow sensing for detection of vortex shedding from airfoils in unsteady flows

Abstract

Sensing of vortex shedding in unsteady airfoil flows can be beneficial in controlling and positively harnessing their effects for increased aerodynamic performance. The time variation of the leading-edge suction parameter (LESP), which is a non-dimensional measure of the leading-edge suction force, is shown to be useful in deducing the various events related to vortex shedding from unsteady airfoils. The recently developed leading-edge flow sensing (LEFS) technique, which uses a few pressures in the airfoil leading-edge region for deducing the aerodynamic state of an airfoil, is adapted to deduce the variation of LESP during an unsteady motion in incompressible flow. For this purpose, the flow over the airfoil is divided into an outer-region flow over the chord, modeled using thin airfoil theory, and an inner-region flow over the leading edge, modeled as a flow past a parabola. By matching these two flows, relations are derived for calculating the LESP from a few pressures at the leading edge. By studying the variations of the LEFS outputs and the calculated LESP for various unsteady motions, guidelines are presented for detecting events related to vortex shedding: initiation, pinch-off, and termination. Computational and experimental results for additional unsteady motions confirm the effectiveness of the LEFS as a sensing technique for events associated with vortex shedding on unsteady airfoils.

Experimental quantification of unsteady leading-edge flow separation

“…The idea of a maximal amount of supported leading-edge suction at stall is also employed as a vorticity release criterion for discrete vortex methods (Ramesh et al 2014;Hou, Darakananda & Eldredge 2019;Narsipur et al 2020). Saini, Narsipur & Gopalarathnam (2021) used this leading-edge suction criterion to detect vortex shedding, together with a leading-edge flow sensing method to control aerofoils in unsteady flow. The leading-edge suction parameter is also a reliable tool to forecast the load response of an incident gust and other external disturbances (Darakananda et al 2018;Le Provost & Eldredge 2021).…”

“…The strategy was recently adopted by Ramesh (2020) to define the leading-edge suction based on the local flow field at the leading edge and linked to the first term of the Fourier coefficient of the thin-aerofoil theory. Saini et al (2021) also used it as a leading-edge flow sensing method, estimating the angle of attack and incoming flow speed. Yet, this approach still relies on a Kutta condition at the trailing edge.…”

“…2020). Saini, Narsipur & Gopalarathnam (2021) used this leading-edge suction criterion to detect vortex shedding, together with a leading-edge flow sensing method to control aerofoils in unsteady flow. The leading-edge suction parameter is also a reliable tool to forecast the load response of an incident gust and other external disturbances (Darakananda et al.…”

“…Saini et al. (2021) also used it as a leading-edge flow sensing method, estimating the angle of attack and incoming flow speed. Yet, this approach still relies on a Kutta condition at the trailing edge.…”

Experimental Study of Dynamical Airfoil and Aerodynamic Prediction

“…Zhou et al [24] explained the physical relationship of pressure data and then developed an offline-online method to sense the real-time aerodynamic parameters. Saini et al [25] developed the leading-edge flow sensing technique, which uses a few pressures in the airfoil leading-edge to identify and sense various flow events associated with vortex shedding in unsteady airfoils.…”