Internal flow of fluidic oscillators

Abstract

Fluidic oscillators are devices that generate a temporally oscillating jet when supplied with a fluid under pressure. In recent investigations fluidic oscillators have proven to be very efficient in active flow control applications, while only little is known about the internal working mechanism of these devices. This thesis presents the internal flow structures and operating frequencies of multiple small-scale fluidic oscillator types for a range of subsonic inlet velocities. Time-resolved visualization of the flow structures inside the fluidic oscillators has been achieved by tracking the shadow of cornstarch particles suspended in the airflow. The application of this particle shadow velocimetry technique to the complex internal flow of fluidic oscillators has resulted in a detailed overview of the different internal flow fields, aided by two-dimensional numerical simulations. These simulations were performed for a wider range of flow rates, thereby extending the parameter range beyond what could be measured experimentally. Using the numerical results an empirical model is formulated, relating the flow rate and internal surface area of the presented fluidic oscillators to an oscillation frequency of the exit jet.