Active Flow Control Upon Cavities At Low Reynolds Numbers

Abstract

Flow past open cavities is well known to give rise to highly coherent and selfsustained oscillations. The oscillations lead to undesirable aeroacoustic resonance. The self-sustained oscillations arise from a feedback loop which is formed as a result of successive events that take place in sequence: roll up of the separating shear layer that is convectively unstable, formation of vortices, vortices hitting the trailing edge of the cavity, propagation of the generated acoustic wave toward to the leading edge, and the receptivity process at the leading edge which set the initial amplitude and phase of the instability waves in the separating shear layer. In particular, when the process is coupled with an acoustic resonance, an intense aerodynamic noise is radiated from the cavity. This character is common to basically all cavity noises regardless of the Mach number. This type of aeroacoustic noise is referred as the cavity noise. But there are scarce bibliography regarding cavity flow control under free incident turbulent flows. So, our main interest is boundary layer control using cavity flows. On doing that we study the characteristics of the cavity flow when the incident free stream is turbulent and how to achieve some control on its vortex pattern inside and the surroundings, and the developed turbulent boundary layer outside the cavity. We intend to use the cavity flow generated as a active flow control system to manage the turbulent boundary layer outside it, using a suction and/or blowing system inside it. An experimental setup was made in order to study the vortex behavior and its incidence on the turbulent boundary layer configuration. As results we show the vortex generated inside the cavity and the turbulent boundary layer behavior related to them, also we include the vortex flow control system instrumentation and characterization.