This paper describes test results of a joint NASA/Boeing research effort to advance Active Flow Control (AFC) technology to enhance aerodynamic efficiency. A full-scale Boeing 757 vertical tail model equipped with sweeping jets AFC was tested at the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel at NASA Ames Research Center. The flow separation control optimization was performed at 100 knots, a maximum rudder deflection of 30deg, and sideslip angles of 0deg and -7.5deg. Greater than 20% increments in side force were achieved at the two sideslip angles with a 31-actuator AFC configuration. Flow physics and flow separation control associated with the AFC are presented in detail. AFC caused significant increases in suction pressure on the actuator side and associated side force enhancement. The momentum coefficient (C sub mu) is shown to be a useful parameter to use for scaling-up sweeping jet AFC from sub-scale tests to full-scale applications. Reducing the number of actuators at a constant total C(sub mu) of approximately 0.5% and tripling the actuator spacing did not significantly affect the flow separation control effectiveness.

/pdf/flow-separation-control-on-a-full-scale-vertical-tail-model-2x7rcslb1u.pdf

Flow Separation Control on A Full-Scale Vertical Tail Model Using Sweeping Jet Actuators

The presented work provides a technical summary of the fundamental time-resolved properties of a spatially oscillating jet emitted by a fluidic oscillator. The discussion focuses on experiments inv...

Fundamental Properties of Fluidic Oscillators for Flow Control Applications

An innovative schlieren system design is introduced using two off-the-shelf telescopes instead of large, expensive lenses or mirrors. Schlieren is used in combination with a high-speed camera to investigate the internal dynamics of sweeping jet actuators. These devices are of particular interest due to their great success in active flow control applications for aerodynamic purposes. Their working principle based on schlieren images is discussed in detail based on a first model. An extended theory based on nondimensional frequency and jet velocity is introduced. A second model consisting of two adjacent sweeping jet actuators is investigated on their interaction characteristics by tracking their motion in the acquired schlieren images and the subsequent analysis of the relative deflection of the jets using fast Fourier transform, phase information, and the Hilbert transform. This is performed for multiple separation distances and two pressure ratios, leading to an underexpanded exit jet and a transonic jet. Last, the probability distribution of the deflection angles for both cases is discussed.

Schlieren Visualization and Analysis of Sweeping Jet Actuator Dynamics

Active flow control (AFC) subscale experiments were conducted at the Lucas Wind Tunnel of the California Institute of Technology. Tests were performed on a generic vertical tail model at low speeds...

/pdf/active-flow-control-on-vertical-tail-models-rv3a5mijy5.pdf

Active Flow Control on Vertical Tail Models.

An experimental study is conducted to examine the impact of internal geometry of a fluidic oscillator on its working mechanisms, i.e., the widths of the inlet wedge W1, mixing chamber W2, and exit throat W3, normalized by the width of the inlet throat W0. Using time-resolved particle image velocimetry, the flow dynamics both inside and outside the oscillator are measured simultaneously. The phase-averaged flow fields are obtained using proper orthogonal decomposition analysis based on which the pressure fields are computed. It is found that the external jet spreading angle and the oscillation frequency are proportional to the width of the inlet wedge up to W1/W0 = 2. This is because the inlet wedge controls the feedback flow and accordingly the recirculation bubble in the mixing chamber. At a critical lower value of W1/W0 = 0.8, there is no feedback flow with a stable external sweeping jet. The mixing chamber width W2/W0 controls the size of the recirculation bubble, which has a notable proportional control on the spreading angle. With a small mixing chamber of W2/W0 = 2.9, it is also found that the strong feedback flow can still produce a stable sweeping jet motion but with a small spreading angle. The exit throat width W3/W0 has non-monotonous control on the external jet spreading angle and the oscillation frequency. It is noteworthy that the jet can still produce a stable sweeping motion even with a large value of W3/W0 = 4.2, which can significantly reduce the blocking effect of the exit.

Flow dynamics of a fluidic oscillator with internal geometry variations

The size of the vertical tail and rudder of a commercial aircraft is influenced by the requirement that the airplane must be controllable in the event of an engine failure. As a result, on twin-eng...

Flight Test of an Active Flow Control Enhanced Vertical Tail

Full-scale Flight Demonstration of an Active Flow Control Enhanced Vertical Tail

Example active flow control systems and methods for aircraft are described herein An example method includes supplying pressurized air to a plurality of nozzles The nozzles arranged in an array across a control surface of an aircraft, and the nozzles are oriented to eject the pressurized air in a substantially streamwise direction The method further includes activating the nozzles to eject the pressurized air in sequence to create a wave of air moving in a spanwise direction across the control surface

Paul Vijgen

Papers

Flight Test of an Active Flow Control Enhanced Vertical Tail

Full-scale Flight Demonstration of an Active Flow Control Enhanced Vertical Tail

Active flow control systems and methods for aircraft