Control of a Transonic Shock in a Serpentine Diffuser using Surface Fluidic Actuation

The total pressure losses and distortion in a serpentine diffuser over a range of flow rates that result in the formation of a transonic shock at the diffuser’s first convex turn are alleviated using fluidic-based flow control. The present investigations show that the shock strength is highest at the diffuser’s spanwise corners and has a local minimum at midspan. Flow distortions above the diffuser’s convex bottom surface are induced by two counterrotating streamwise vortices that originate at each corner and strengthen as a result of interaction of the corner flow with the shock. These vortices are controlled indirectly by manipulation of the shock using a spanwise array of fluidic oscillating jets that are integrated into the diffuser moldline upstream of the shock. It is shown that along with changing the shock footprint topology, flow control displaces the streamwise vortex pair farther apart and thereby diminishes the cooperative advection of a low momentum fluid from the wall region into the core flow. Consequently, the average circumferential distortion parameter is reduced by 35%, while the total pressure recovery increases by about 1%. These findings indicate that diffuser flow rates higher than the nominal operating condition, which are typically limited by shock losses, can be enabled by active flow control.