Unsteady Flow Evolution in Porous Chamber with Surface Mass Injection, Part 2: Acoustic Excitation

Our earlier work on injection-driven eows in a porous chamber is extended to explore the effect of forced periodic excitations on the unsteady eoweeld. Time-resolved simulations are performed to investigate the effects of traveling acoustic waves on large-scale turbulent structures for various amplitudes and frequencies of imposed excitations. The resultant oscillatory eowe eld is decomposed into mean, periodic (or organized), and turbulent (or random)motions using a time-frequency localization technique. Emphasis is placed on the interactions among the three components of the e oweeld. The primary mechanism for the transfer of energy from the mean to the turbulentmotionisprovidedbythenonlinearcorrelationsamongthevelocityeuctuations,asobservedinstationary turbulent eows.Theunsteady, deterministiccomponent gives risetoan additional mechanismforenergyexchange between the organized and turbulent motions and, consequently, produces increased turbulence levels at certain acoustic frequencies. The periodic excitations lead to earlier laminar-to-turbulence transition than that observed in stationary eows. The turbulence-enhanced momentum transport, on the other hand, leads to increased eddy viscosity and tends to dissipate the vortical wave originating from the injection surface. The coupling between the turbulent and acoustic motions results in signie cant changes in the unsteady eow evolution in a porous chamber.