Transport phenomena in subsonic and supersonic flows in a duct with mass injection.

Abstract

Film cooling effects have always been crucial for the engine/rocket/ramjet propulsion systems. Knowing the pressure and temperature distribution of the flow is very important for both system and structural analyses to find optimal design. An efficient time dependent, compressible Navier-Stokes solver using higher order accuracy algorithms employing the finite-volume method is developed for this work. The physics inside the flow field with a cooler secondary mass stream injected into the channel is studied. The results showed that for subsonic main flow, the injected mass stream will bend and accelerate in the downstream direction, and creating a region of lower temperature near the downstream walls. This lower temperature region also exists even if there is a heat flux added to the flow system. Therefore, film cooling effect exists for the subsonic flow. For supersonic flow, however, the injected mass flow, instead of bending toward the downstream wall in order to have a cooling effect, is bent toward upstream direction and retards the main flow, resulting in a stagnant flow region. The temperature in the entire flow field is found to increase an appreciable amount even though the temperature in the stagnant region is found to be relatively lower than other areas. Therefore, there is no film cooling effect observed for supersonic flow. These phenomena have been verified by the experimental work. For subsonic flow, the acoustical wave is found to travel forwards and backwards in the field system while the pressure gradient is favorable for the whole flow field. For supersonic flow, there is always an adverse pressure gradient region formed near the walls upstream of the mass-injection location. Inside this adverse pressure gradient region, an air bubble is usually found to exist. The flow interactions between the main stream and secondary stream increase the flow vorticity. This vorticity is found to travel in the downstream direction for subsonic flow. However, for supersonic flow, this vorticity is found to travel in both the upstream and the downstream directions.