NASA’s Langley Research Center develops innovative technologies to control fluid flow in ways that will ultimately result in improved performance and fuel efficiency. Often called fluidic oscillators, sweeping jet actuators, or flip flop oscillators, these flow-control devices work based on the Coanda effect. They can be embedded directly into a control surface (such as a wing or a turbine blade) and generate spatially oscillating bursts (or jets) of fluid to improve flow characteristics by enhancing lift, reducing drag, or enhancing heat transfer. Recent studies show up to a 60% performance enhancement with oscillators. NASA offers two new fluidic oscillator designs that address two key limitations of these oscillators: coupled frequency-amplitude and random oscillations. One oscillator effectively decouples the oscillation frequency from the amplitude. The other design enables synchronization of an entire array. The new oscillators have no moving parts — oscillation, decoupling, and synchronization are achieved entirely via internal flow dynamics.
The first design decouples frequency and amplitude. Existing oscillators are limited in that the frequency of oscillation is controlled by input pressure or mass flow rate. The frequency and amplitude (mass flow rate) are coupled, limiting control authority over the oscillators. The new oscillator design decouples the frequency from the amplitude by employing a novel design featuring a main oscillator that controls the amplitude and a small oscillator that controls the frequency of the oscillations. The decoupled oscillator delivers high (or low) mass flow rates without changing the frequency and vice versa.
The second design synchronizes the entire oscillator jet array. Existing oscillators in an array oscillate randomly. While this is useful for mixing enhancement, synchronized flow may be more beneficial for active flow-control applications. The simple design of the new Langley synchronized oscillator achieves synchronization without having electro/ mechanical or any other moving parts. The new oscillator enables synchronization of an entire array by properly designing the feedback loops to have one unique feedback signal to each actuator. Once each actuator has the same feedback signal, each main jet attaches to one side of the Coanda surface at the same time, allowing synchronized oscillation.
These fluidic oscillator designs are rugged and can be used in harsh environments. In addition, they are scalable from micro to macro size, and can be machined as embedded arrays. This technology can be used in aerospace applications for boundary layer control, separation control, lift enhancement, drag reduction, and mixing; in shipbuilding for flow control; in gas turbines for heat transfer enhancement and separation control; and in commercial spa equipment for improved nozzle performance.