Delta Wing Stall and Roll Control Using Segmented Piezoelectric Fluidic Actuators

Abstract

The separated flow around a balance-mounted, 60-deg sweptback, semispan delta wing with a sharp leading edge was controlled using zero-mass-flux periodic excitation from a segmented leading-edge slot. Excitation was generated by cavity-installed piezoelectric actuators operating at resonance with amplitude modulation (AM) and burst mode (BM) signals being used to achieve reduced frequencies (scaled with the freestream velocity and the root chord) in the range from O(1) to O(10). Results of a parametric investigation, studying the effects of AM frequency, BM duty cycle and frequency, excitation amplitude, location of the actuation along the leading edge, and optimal phase difference between the actuators, as well as the Reynolds number, are reported and discussed. Balance data were supplemented by upper surface static pressure measurements and particle image velocimetry (PIV) data. Order unity reduced-frequency modulation of the high-frequency carrier wave increased the normal force generated by the delta wing most effectively. BM with a duty cycle that was as low as 5% was more effective than the amplitude-modulated signal with larger peak excitation velocity and an order of magnitude larger momentum input. PIV data suggest that excitation enhances the momentum transfer across the shear layer, downstream of the original vortex breakdown location, generating a streamwise vortex the size of which is commensurate with the local wing span. Nomenclatureleading-edge length D = drag force DCy = duty cycle, n f m / f r FM = figure of merit, η/(C L /C D ) baseline F + = nondimensional excitation frequency, ( f c/U ∞ ) f = excitation frequency; either f m or f r , depends on excitation type f m = modulating frequency f r = actuators resonance frequency K = number of active actuator elements L = length of separated region n = number of excitation cycles p = local pressure Q = in-plane velocity, √ (w 2 + v 2 ) q = freestream dynamic pressure, ρU 2 ∞ /2 Re = root chord Reynolds number, U ∞ c/ν T m = input signal modulation period T r = period of actuators' sine wave U p = slot exit peak velocity U ∞ = freestream velocity u f = fast Fourier transform amplitude results at f = f m u = rms of velocity fluctuations u s = u at the slot's exit V rms = rms excitation voltage v, w = velocity components of the flow in the y, z directions W= actuator input power, W X R = distance from actuator to reattachment area X TE = distance from actuator to trailing edge x, y, z = Cartesian coordinates, (Fig. 1) x , y = rotated coordinates, (Fig. 1) α = angle of attack α s = stall α η = aerodynamic efficiency, C L /(C D + C E ) η R = spanwise location of the center of pressure, origin at tunnel wall, C R /C N ν = kinematic viscosity ρ = air density = phase angle between input signals to each actuator χ M = streamwise location of the center of pressure, origin at midchord, C M /C N = dimensionless vorticity, (∂v/∂x − ∂u/∂ y)/U ∞ c

Alleviating Unsteady Aerodynamic Loads with Closed-Loop Flow Control

“…A few actuation methods that have proven to be successful for producing time-varying lift include 1) variablestrength "steady" jets [3,43], 2) variable-amplitude burst-mode actuation with synthetic jets [44][45][46][47], 3) burst-mode combustion actuators [48][49][50][51], and 4) variable-voltage dielectric barrier discharge plasma actuators [52,53].…”

Influence of Finite Span and Sweep on Active Flow Control Efficacy

“…[3,4] Control by pulse-modulation of high frequency piezo-electric actuators generated maximum lift at F + =O(1). [5] PIV measurements suggested that the pulsing enhances momentum transfer across the shear layer, downstream of the original vortex breakdown location, and generates a streamwise vortex whose size is commensurate with the local wingspan.…”

“…A number of AFC investigations have also been carried out on delta wings and highly swept planforms. [3][4][5][6] Control extended vortex breakdown by about 25%, thereby generating increased lift. [3,4] Control by pulse-modulation of high frequency piezo-electric actuators generated maximum lift at F + =O(1).…”

Active Flow Control on a UCAV Planform Using Synthetic Jets

“…Through unsteady actuation, the synthetic jets can exploit the instability of the separating shear layer, which results in a Coanda-like unsteady reattachment [4]. Other researchers have attempted to control the separated flow using a cylinder [5,6], 2D airfoils [4,7,8], tilt-rotor UAVs [9], or a simple geometric delta wing [10]. The results demonstrated that actuation is quite effective under variable flow conditions [11].…”