Dynamics of an Internal Flowfield Driven by Two Hydrodynamic Instabilities

Hydrodynamic instabilities in a confined flow generated by air injection through porous walls separated by an emerging obstacle are experimentally characterized. Two different mechanisms of instabilities have been detected: a vortex shedding phenomenon back to the obstacle location and one developing along the porous wall. The latter was found to provide most of the acoustic energy. Influence of an unbalanced mass flow rate between each side of the obstacle has been carried out over a wide range of mean velocities; an increase of the mass flow rate injected downstream of the obstacle implies resonance amplification by wall vortex shedding that strengthens the instabilities in the chamber. On the other hand, an increase in the mass flow rate upstream from the obstacle location favors vortex pairing and self-sustained oscillations, whereas acoustic wave generation by wall vortex impingement is weakened. [PUBLICATION ABSTRACT]