An experimental investigation of the mixing of coannular swirling flows

An extensive investigation of the mixing behavior of coannular streams, with swirl present, has been carried out. A large blowdown facility was adapted to provide two streams of air at variable stagnation pressures but equal stagnation temperatures. Conditions within the mixing region were essentially incompressible. The facility was constructed to provide swirl in the inner stream, and a fixed inner and outer annulus could be provided if desired. In all cases considered, swirl was present in the inner but not the outer stream, thereby leading to flow conditions unstable to the Rayleigh instability. Mean flow measurements only were obtained. A five-hole probe was used to obtain the static pressure, stagnation pressure, and three velocity components. Additional measurements included sidewall pressure measurements on the inner and outer annuli, as well as stream mass flow rates obtained from orifice plate meters. A variety of flow regimes were considered, including some without separated regions present. Where possible, the results were compared to the somewhat limited data available in the literature.