Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

Abstract

High-fidelity simulations are performed to study active flow control techniques for alleviating deep dynamic stall of a SD7003 airfoil in plunging motion. The flow Reynolds number is Re = 60,000 and the freestream Mach number is M = 0.1. Numerical simulations are performed with a finite difference based solver that incorporates high-order compact schemes for differentiation, interpolation and filtering on a staggered grid. A mesh convergence study is conducted and results show good agreement with available data in terms of aerodynamic coefficients. Different spanwise arrangements of actuators are implemented to simulate blowing and suction at the airfoil leading edge. We observe that, for a specific frequency range of actuation, mean drag and drag fluctuations are substantially reduced while mean lift is maintained almost unaffected, especially for a 2D actuator setup. For this frequency range, 2D flow actuation disrupts the formation of the dynamic stall vortex, what leads to drag reduction due to a pressure increase along the airfoil suction side, towards the trailing edge region. At the same time, pressure is reduced on the suction side near the leading edge, increasing lift and further reducing drag.

Extremum Seeking Control Applied to Airfoil Trailing-Edge Noise Suppression

“…Some of the values for 𝐴 used in this work are: 0.060 (𝐶 𝜇 ≈ 1.511𝑒 − 3), 0.030 (𝐶 𝜇 ≈ 3.778𝑒 − 4) and 0.012 (𝐶 𝜇 ≈ 6.045𝑒 − 5). These values resemble those found in literature[23,[43][44][45] for flow actuation in airfoil flows. The variation of 𝐶 𝜇 along the wall with moving actuation is under 1% above and below the average.…”

“…In the present work, extremum seeking control is applied for real-time minimization of acoustic noise emitted by an airfoil. The pertinent control modules are implemented in a high-fidelity CFD simulation tool that has been validated for compressible flow applications [23,31]. Besides the ESC approach, some investigations proposed in this work alternatively use slope seeking control, which is suitable for cost functions that exhibit plateaus.…”

“…The improvement in computational power and novel developments in control theory [17,18] enabled high-fidelity simulations of complex unsteady flows together with active flow control. The combination of computational fluid dynamics (CFD) and active control strategies has been shown by several authors [19][20][21][22][23][24]. Yeh and Taira [22] applied resolvent analysis to airfoil large eddy simulation data in order to find the best open-loop control parameters of a periodic heat flux actuator near the leading edge.…”

“…In a numerical environment, the authors presented a study on how the controller modifies the flow in different configurations, and how it affects aerodynamic properties such as lift and pitching moment. Further studies on airfoil dynamic stall control were conducted by Ramos et al [23]. These authors investigated the actuator spanwise arrangement and frequency that provided drag reduction for a plunging airfoil by modifying the formation of the dynamic stall vortex and, hence, the unsteady pressure distribution around the airfoil.…”

Transition, intermittency and phase interference effects in airfoil secondary tones and acoustic feedback loop

“…Herein, time and frequency (Strouhal number) are presented non-dimensionalised by freestream velocity as t = t * U * ∞ /L * and St = f * L * /U * ∞ , respectively. The present numerical methodology has been extensively validated for various 2-D and 3-D simulations of compressible airfoil flows at different configurations (Wolf et al 2012a,b;Wolf, Azevedo & Lele 2013;Ramos et al 2019).…”