Fluidic-Oscillator-Based Pulsed Jet Actuators for Flow Separation Control

Abstract

The control of flow separation on aerodynamic surfaces remains a fundamental goal for future air transportation. On airplane wings and control surfaces, the effects of flow separation include decreased lift, increased drag, and enhanced flow unsteadiness and noise, all of which are detrimental to flight performance, fuel consumption, and environmental emissions. Many types of actuators have been designed in the past to counter the negative effects of flow separation, from passive vortex generators to active methods like synthetic jets, plasma actuators, or sweeping jets. At the Chair of Aerodynamics at TU Berlin, significant success has been achieved through the use of pulsed jet actuators (PJA) which operate by ejecting a given amount of fluid at a specified frequency through a slit-shape slot on the test surface, thereby increasing entrainment and momentum in a separating boundary layer and thus delaying flow separation. Earlier PJAs were implemented using fast-switching solenoid valves to regulate the jet amplitude and frequency. In recent years, the mechanical valves have been replaced by fluidic oscillators (FO) in an attempt to generate the desired control authority without any moving parts, thus paving the way for future industrial applications.

Current state and future trends in boundary layer control on lifting surfaces

“…Schematics of: (a) fluidic oscillators, 102 (b) wall-normal pulsed jets, 108 (c) hybrid SJA, 119 (d) DBD actuators, 129 (e) moving walls, 13 and (f) deforming wall patch. 155 …”

“…Their oscillatory operation is usually achieved mechanically, or, in recent years, by fluidic oscillators (actuators constituted of a flow vane with no moving parts, using steady suction and oscillatory blowing, have been thoroughly investigated in previous years). More analytical and explanatory material on fluidic oscillators is available in Lo¨ffler et al 102 (Figure 4(a)). Various types of PJAs are mentioned here, and their applications are truly extensive.…”

Editorial for the Special Issue on “Fluidic Oscillators—Devices and Applications”

“…This Special Issue, titled "Fluidic Oscillators-Devices and Applications", captures a few examples of current topics involving fluidic oscillators, ranging from flow control over combustion applications to various industrial systems. The use of fluidic oscillators for active flow control purposes remains a focus area of the scientific community, as showcased by Löffler et al [18] and Koklu [19]. Liebsch and Paschereit [20] discuss the use of active flow control with fluidic oscillators for an industrial application to reduce flow separation and recirculation of harmful gases in laboratory fume hoods.…”

Jet Velocity and Acoustic Excitation Characteristics of a Synthetic Jet Actuator

“…Previous work on synthetic jet actuators (SJAs) has proven their potential to delay flow separation over critical aerodynamic surfaces [1][2][3][4]. Like many other active flow control techniques [5,6], SJAs have the promising aspect of being tuned to control-separated flow in different conditions. In this technology, flow control is achieved by injecting flow via the external excitation of an enclosed cavity volume.…”