Near Stall Unsteady Flow Responses to Morphing Flap Deflections

Abstract

The unsteady flow characteristics and responses of an NACA 0012 airfoil fitted with a bio-inspired morphing trailing edge flap (TEF) at near-stall angles of attack (AoA) undergoing downward deflections are investigated at a Reynolds number of 0.62 × 106 near stall. An unsteady geometric parametrization and a dynamic meshing scheme are used to drive the morphing motion. The objective is to determine the susceptibility of near-stall flow to a morphing actuation and the viability of rapid downward flap deflection as a control mechanism, including its effect on transient forces and flow field unsteadiness. The dynamic flow responses to downward deflections are studied for a range of morphing frequencies (at a fixed large amplitude), using a high-fidelity, hybrid RANS-LES model. The time histories of the lift and drag coefficient responses exhibit a proportional relationship between the morphing frequency and the slope of response at which these quantities evolve. Interestingly, an overshoot in the drag coefficient is captured, even in quasi-static conditions, however this is not seen in the lift coefficient. Qualitative analysis confirms that an airfoil in near stall conditions is receptive to morphing TEF deflections, and that some similarities triggering the stall exist between downward morphing TEFs and rapid ramp-up type pitching motions.

Effects of an Unsteady Morphing Wing with Seamless Side-Edge Transition on Aerodynamic Performance

“…The laminar trans to turbulent BL is clearly captured as seen in the sudden increase of Cf, and it appear the transition gets closer to the LE the more the main flap is deflected, indicating tha transition has some connections with the LSB. A similar conclusion was drawn in a ence paper [37] when the Stress-Blended Eddy Simulation (SBES) model was used a These predictions may be more realistic compared with the statically morphed wing, as in real-life scenarios, the flap is deployed dynamically which gives rise to unsteady flow phenomena (e.g., vortex formation and convection downstream) that could influence the aerodynamic performance, such as the sudden peaks in drag observed before the final TEF position.…”

“…Moreover, the intermittency k-ω SST model is used for turbulence closure, and a second order upwind scheme is utilized for the momentum and turbulence equations discretization. The intermittency k-ω SST has been chosen as it offers a good balance between the accuracy and computational cost, it has been shown that it is perfectly adequate for this type of turbulent separated flow [47], offering better predictions than the Spalart-Allmaras model [48], but at only a fraction of the cost compared to higher fidelity turbulence models, such as the hybrid SBES which has been used in previous published 2D work [37].…”

“…Of course it is possible that improved predictions for drag coefficient may be obtained using advanced turbulence models, as demonstrated by Arko and McQuilling [52], who used the advanced turbulence models of Abe et al [51] to improve drag predictions in the post stall. Also, Abdessemed et al [37] used Stress-Blended Eddy Simulation modelling to improve 2D airfoil flow prediction. However, given the increased computational resources that already exists in a Energies 2022, 15, 1093 10 of 27 3D dynamically morphing configuration, the current predictions were deemed satisfactory for the purpose of this paper, especially that the morphing configuration and its settings are merely compared relatively to each other, rather than to an absolute accuracy.…”

“…All of the studies surveyed to date have simplified the wing morphing to be a statically morphed wing configuration, thereby overlooking the dynamic effects that deforming motion of the TEF might have on the flow field and its subsequent contribution to the airframe noise. Abdessemed et al [34][35][36][37][38] have previously introduced a framework to study 2D unsteady morphing airfoils by modifying a parametrization method to include a time variable and integrating it into a high-fidelity RANS solver [39] with the help of an in-house developed user-defined function (UDF) routine [40] to accommodate a dynamic meshing for mesh deformation. Nevertheless, to capture the physics of real-life morphing wings, the problem needs to be considered in 3D, allowing the turbulence to be properly resolved, and a more realistic morphing concept to be modelled, particularly the spanwise effects on the flow field.…”

“…The seamless transition is based on a recent concept, known as Morphing Elastically LofteD (MELD), introduced by Woods et al [25], which still lacks quantitative performance analysis. Secondly, an extension to the above work by investigating the unsteady aerodynamic effects of a morphing wing [34][35][36][37] is proposed in order to study a dynamically morphing TEF with a seamless side-edge transition (where the TEF deforms continuously from a baseline position to a final deflection). A modified seamless transition function is proposed and used to model the transition between the static and morphing parts of the wing.…”