A numerical study was conducted to investigate the effect of an array of zero-mass "synthetic" jets on the aerodynamic characteristics of the NACA-0012 airfoil. Flowfield predictions were made using a modified version of the NASA Ames "ARC2D" unsteady, two-dimensional, compressible Navier-Stokes flow solver. An unsteady surface transpiration boundary condition was enforced over a user-specified portion of the airfoil's upper or lower surface to emulate the time variation of the mass flux out from and into the airfoil's surface. Here, a sinusoidal function which describes the approximate time behavior of the mass flux across the airfoil's surface was used. Our numerical results have indicated that zero-mass jets can, with the careful selection of their peak amplitude and frequency, enhance the lift characteristics of airfoils (helicopter rotor blades, wings, etc.). Effects of the jet peak suction and blowing velocities, oscillation frequency and, jet placement on the time histories of the sectional lift, drag and moment are presented for two angles of attack and one free stream Mach number. Flowfield results which provide more insight into the mechanics of the interaction between the array of jets and the developing boundary layer over the airfoil are presented.

Results from a joint DARPA/Boeing/NASA/Army wind tunnel test demonstrated the ability to reduce in-plane, low-frequency noise of the full-scale Boeing-SMART (Smart Material Actuated Rotor Technology) rotor with active flaps. Test data reported in this paper illustrated that near-field acoustic energy in the first six blade-passing harmonics could be reduced by up to 6 dB at a moderate-airspeed, level flight condition at an advance ratio of 0.30. Reduced noise levels were attributed to selective active flap schedules that modified in-plane blade airloads on the advancing side of the rotor, generating counteracting acoustic pulses that partially offset the negative pressure peaks associated with in-plane, steady thickness noise. These favorable reduced-noise operating states are a strong function of the active flap actuation amplitude, frequency, and phase. The reduced noise levels resulted in reduction of predicted aural detection distance, but incurred vibratory load penalties due to increased hub shear forces.

A numerical study was conducted to investigate the effect of an array ofzero-mass "synthetic" jets on the aerodynamic characteristics of the NACA-0012 airfoil. Flowfield predictions were made using a modified version of the NASA Ames "ARCZD" unsteady, hvo-dimensional, compressible Navier-Stokes flow solver. An unsteady surface transpiration boundary condition was enforced over a user-specified portion of the airfoil's upper andlor lower surface to emulate the time variation of the mass flux out from and into the airfoil's surface. Here, a sinusoidal function which describes the approximate time behavior of the instantaneous mass flux across the airfoil's surface was used. Numerical results have indicated that zero-mass jets can, with the careful selection of their peak amplitude and frequency, enhance the lift characteristics of airfoils (helicopter rotor blades, wings, etc.). Effects of the jet peak suction and blowing velocities, oscillation frequency, and jet surface placement on the time histories of the sectional lift, drag and moment are presented for hvo angles of attack and a free stream Mach number of 0.60. Flowfield results that provide insight into the mechanics of the interaction behveen the array of jets and the developing houndary layer over the airfoil are presented.

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