Variable Frequency Diverter Actuation for Flow Control

Abstract

• E-mail your question via the Internet to help@sti.nasa.gov• Fax your question to the NASA STI Help Desk at 301-621-0134• This report contains preliminary findings, subject to revision as analysis proceeds.The design and development of an actively controlled fluidic actuator for flow control applications is explored. The basic device, with one input and two output channels, takes advantage of the Coanda effect to force a fluid jet to adhere to one of two axi-symmetric surfaces. The resultant flow is bi-stable, producing a constant flow from one output channel, until a disturbance force applied at the control point causes the flow to switch to the alternate output channel. By properly applying active control the output flows can be manipulated to provide a high degree of modulation over a wide and variable range of frequency and duty cycle. In this study the momentary operative force is applied by small, high speed isolation valves of which several different types are examined. The active fluidic diverter actuator is shown to work in several configurations including that in which the operator valves are referenced to atmosphere as well as to a source common with the power stream. I. IntroductionFlow control, broadly defined, is the ability to purposely alter the characteristics of a flowfield in order to extract some overall benefit. More precisely in terms of present day aeronautics technology, flow control implies the intent to correct any local defects in a given flowfield which generally are the result of transitory, three-dimensional effects in a volatile design space. A fixed aeromechanical surface can only be expected to perform optimally over a relatively narrow range of conditions and flow control is viewed as a method in which to extend this useful range. Hence, flow control in aero vehicles and engines is a vigorous area of research. Still the implementation of flow control in actual practice is limited to well-understood and well-behaved techniques such as passive vortex generators and the mechanical articulation of flow surfaces. These passive attempts at flow control are effective and often necessary, however they ultimately limit performance.NASA Glenn Research Center (GRC) is aggressively pursuing new flow control methodologies and applications in future aero-vehicles. These are largely "active" flow control methodologies meaning that when not needed they are not applied. The intent is to minimize the performance penalty which would otherwise be incurred. In a paper by Lord 1 , et al, many opportunities for active flow control within turbomachinery are articulated. Presently, turbinebased propulsion systems require large aeromechanical design margins and make very limited use of scheduled flow control. The design of these systems is typically based on the worst-case requirements seen at take-off and landing and from the expected performance degradation resulting from routine wear during the service life of the engine. In a typical commercial aircraft, however, only during a small portion of the m...

A Review of Fluidic Oscillator Development and Application for Flow Control

“…Gregory et al [35] used a piezoelectric bender to drive the switching process, while Culley [18] used a range of pressure input devices such as solenoid valves. Koklu and Melton [48] also used solenoid valves to drive the oscillation frequency for phase-locked PIV studies.…”

Parameters Governing Separation Control with Sweeping Jet Actuators

“…The characteristics of various actuator types, conceptually similar to the designs shown in Figure 1, have been investigated experimentally [31][32][33][41][42][43][44][45][46][47][48] and numerically [48][49][50][51][52] by numerous researchers. Several active and passive concepts to provide the oscillatory character of the emitted jet have been proposed, including selfinduced feedback [43] and external control [42,[44][45][46][47] designs. Early actuators for flow control used a splitter in the outlet nozzle [36,40,55] , which forced the jet to exit through discrete outlets ( Figure 1a) instead of having a continuous sweeping range ( Figure 1b).…”

Characteristics of a novel fluidic oscillator with movable feedback channels and resonators

“…This approach can change the jet frequency of the oscillator through the K-H instability between the two control jets and the mainstream to generate ultra-high frequency jets. Culley (Culley, 2006) added a solenoid pressure valve to the inlet of the oscillator to regulate the pressure in the control channel and thus control the frequency of the jets generated by the devices. The highest frequency measured from this experimental device is 312 Hz due to the limitations in the switching speed of the solenoid valve.…”