Active Flow Control of a Pitching Turret Flow Field Using Closed-Loop Feedback Control

Abstract

Experimental testing of an active flow control system on a three-dimensional, nonconformal turret has been performed at a diameter based Reynolds number of 2.0 × 10 6 . Active flow control was achieved using dynamic suction and various open and closed-loop feedback control algorithms in an effort to determine the most effective and efficient control scheme for reducing aero-optic distortions in the vicinity of the turret aperture. Dynamic surface pressure and PIV measurements have been used to better characterize and understand the flow field in order to evaluate the active control system. From this research, it has been shown that dynamic suction has the ability to manipulate the separated flow above the turret aperture and can significantly alter the characteristics of the aperture flow field. Open-loop control was shown to be the most efficient form of control when set to the proper suction levels, but the merit of closed-loop feedback control has also been shown, especially for cases where the aperture of the turret is dynamically pitching. Generally, open-loop control systems require scheduling of the active control system during pitching where a closed-loop control system would not due to the sensing capabilities. Nomenclaturẽ a n = Estimation of POD expansion coefficient a n = POD expansion coefficient A J = Suction slot area A o = Frontal area of turret A ni = Linear coefficients of MLSM C µ = Jet momentum coefficient D = Turret diameter DC = Duty cycle eã n = MLSM estimation error f p = Turret pitch frequency in Hertz P = Fourier transform of pressure signal p = Time dependent pressure signal Re D = Diameter based Reynolds number S j,k = Cross-spectral density function T = Block sampling time t = Time U = Streamwise velocity component u i = i th component of velocity U ∞ = Freestream velocity U J = Suction jet velocity u RMS = Fluctuating RMS velocity θ = Turret pitch angle φ (n) i = Mode n POD eigenfunction ρ ∞ = Freestream density ρ J = Density of suction jet flow ξ = Controller efficiency * Graduate Student, Department of Mechanical and Aerospace Engineering, 263 Link Hall, and AIAA Student Member.

Closed-Loop Active Flow Control of a Three-Dimensional Turret Wake

“…Operating outside of this range resulted in inconsistent response from the valves, which was undesirable. It is also important to note that, although the 15 Hz driving frequency is not fast enough to respond to the natural timescales of the flowfield, this control rate is satisfactory for control at the timescales associated with pitching the turret (see, e.g., Wallace et al [13] and Shea et al [19]). Figure 13 shows example time traces of the DC and corresponding valve driving signals for the SCLC configuration.…”

“…The dynamic turret has additional timescales associated with the pitching or yawing of the optical systems, and these timescales can be much lower than the natural flow frequencies. Past work has shown that performing closed-loop flow control at these timescales can be more efficient than open-loop control [13,19].…”

“…Initial active flow control studies performed by Andino et al and Andino and Glauser investigated the use of synthetic jet actuators on the static geometry [11,17]. More recent studies by Wallace et al and Shea et al investigated the effect of suction-based flow control on dynamic geometries, in which the turret aperture had prescribed motion in either the pitch or yaw direction [13,18,19]. As part of these studies, parametric evaluations of the static pitch and yaw angles were also performed.…”