Fluidic oscillators: decoupling amplitude and frequency

Abstract

The purpose of this thesis is to find a way to decouple the amplitude and the frequency of the oscillatory jet in the output of a fluidic oscillator by modifying a geometrical parameter and the Reynolds number, with the assistance of computational fluid dynamics (CFD). Fluidic oscillators are a type of active flow control that can be used to delay boundary layer separation, a problem that arises in aircraft wings when facing the airstream at a high angle of attack that causes a sudden decrease in lift and a high increase in drag. Fluidic oscillators improve this situation by injecting an oscillatory jet into the boundary layer, which converts the boundary layer into a turbulent one that can stay attached to the wing for longer. The advantage of the fluidic oscillator with respect to other active flow control devices is that, in its core design, it contains no moving parts, making it more robust than the rest. The version of the fluidic oscillator used in this study has been simplified with the design target of having a geometric parameter that can be modified during operation. The results focus on the internal dynamics of the fluidic oscillator and in the dependence of the amplitude and the frequency with respect to the Reynolds number and the geometric parameter, both separately and together. They show that the amplitude and frequency increase and decrease, respectively, with both an increasing Reynolds number and an increasing geometric parameter, within the operational range of the fluidic oscillator. This allows for both parameters to be modified independently but in limited increments, due to the similar behavior between changing the Reynolds number and the geometric parameter.