Nathan Webb

Preliminary Results on Shock Wave/Boundary Layer Interaction Control Using Localized Arc Filament Plasma Actuators

Localized Arc Filament Plasma Actuators (LAFPAs) are used to excite natural instabilities within a shock wave / boundary layer interaction for separation control. A newly built supersonic wind tunnel with 76.2mm × 76.2mm test section and with a variable-angle wedge shock generator is used. The Mach 2.33 flow in the new facility is characterized using schlieren imaging, streamwise PIV measurements, time-resolved surface pressure measurements, and surface oil flow visualization. The naturally developed boundary layer before the interaction region is fully turbulent with a boundary layer thickness of 5.35 mm and Reynolds number based on boundary layer momentum thickness of 24,800. The unsteadiness observed in the interaction region is similar to the recent experimental and computational results in the literature—the Strouhal number gradually changes from approximately 0.03 to 0.5 in the downstream direction. In this paper, we present characterization of the baseline Mach 2.33 flow with several shock angles.

Supersonic Cavity Control Using Plasma Actuators

Cavity flows are present in a wide range of aerodynamic applications. A cavity could potentially be used in a scramjet isolator as a shock trap to increase the back-pressure margin of the inlet/isolator. In order to avoid a significant drag penalty while maintaining shock-trapping ability, fastresponse resonance suppression is required. Localized Arc Filament Plasma Actuators (LAFPAs) have demonstrated the ability to control a high subsonic cavity flow. 1 This work investigates the control authority of the LAFPAs in a supersonic (M = 2.24) cavity flow. The LAFPAs significantly suppress the primary cavity resonance. Additionally, the trend in effectiveness suggests that inducing mode competition through the excitation of the Kelvin-Helmholtz instability, and thus shear-layer structure formation at the excitation frequency, is likely the control mechanism. The effects of 2-D and 3-D excitation were explored. While 2D excitation achieved the greatest resonance suppression, 3-D excitation showed similar suppression with much less sensitivity to excitation frequency. This likely makes it more suitable for applications such as a shock trap.

An Investigation of the Control Mechanism of Plasma Actuators in a Shock Wave-Boundary Layer Interaction

Shock Wave-Boundary Layer Interaction (SWBLI) induced separation control using Localized Arc Filament Plasma Actuators (LAFPAs) is investigated. The freestream Mach number is 2.3 and the boundary layer is fully turbulent (Re = 27,900). The impinging oblique shock wave is generated by a 10 compression ramp. The reflected shock is displaced upstream by approximately one boundary layer thickness (~ 5 mm) by the LAFPAs. The control objective was to exploit potential natural instabilities within the flow to manipulate the low frequency (St~0.03) unsteadiness associated with the upstream region of the interaction. Parametric studies of the LAFPAs’ effects seemed to indicate that unsteadiness manipulation is not the primary control mechanism but suggest that boundary layer degradation through heating is rather the primary control mechanism. Further examination of the boundary layer and interaction has shown this hypothesis to be correct.

Control of Dynamic Stall over a NACA 0015 Airfoil Using Plasma Actuators

Dynamic stall is observed in numerous applications, including sharply maneuvering fixed-wing aircraft, biomimetics, wind turbines, and most notably, rotorcraft. The associated unsteady loading can ...

Shock-Trapping Capability of a Cavity in a Supersonic Flow

Unstart prevention is a critical part of maintaining stable scramjet operation. An isolator is used to perform this function, but incurs substantial size, weight, and drag penalties. Augmenting an isolator with a cavity could increase the back-pressure margin, allowing a reduction in the isolator size and weight. A resonating cavity could potentially provide the necessary increase in back-pressure margin; however, there is an associated drag penalty. Localized Arc Filament Plasma Actuators (LAFPAs) have demonstrated the ability to enhance or suppress cavity resonance. Thus, a feedback control system could allow the cavity resonance to be suppressed during normal operation, thereby reducing the drag penalty until added back-pressure margin is needed. This work examines the back-pressure margin of a model isolator (straight duct) and the same isolator with a controlled cavity installed at the upstream end. In this preliminary work, the baseline resonating cavity is found to significantly increase the supportable downstream blockage. The ongoing work will explore the effect of resonance enhancement and suppression on cavity drag and shock-trapping capabilities, and eventually feedback control.