Flow simulations have been performed as part of our effort to better understand powered resonance tube behavior. Scaled simulations of the powered resonance tube have produced reasonable correspondence to laboratory experiments, in terms of the frequency and amplitude of the resonant response. The simulations suggest new insights into the complexity and details of the flowfield. The simulations show that the flow in the integration slot is primarily on the resonance tube side, with almost no flow on the supply tube side of the integration slot. The numerical results suggest that the acoustic waves from the resonance in the resonance tube drive an unsteady separation at the supply tube. The unsteady separation at the supply tube in turn drives the observed large oscillations in the shock structure. The unsteady separation seems to be a key aspect of the resonance phenomena. Very recently it has been discovered that for shallow resonance tubes, the pressure ratio affects the response frequency. Also, the resonance tube is found to impose strong pressure disturbances in a Mach 0.5 boundary layer flow. The presence of the Mach 0.5 external stream and boundary layer reduces the resonance frequency by about 12%, relative to the case without an external stream.