Velocity Distribution in an Abruptly Expanding Circular Duct

The behavior of recirculating flows typical of advanced air-breathing and rocket injectors has been experimentally investigated. The configuration used consisted of a circular duct having a sudden increase of its diameter. Step size and flow velocity were chosen to be of a magnitude representative of “sudden-dump” combustion chambers. The recirculation, which occurred in the separation region behind the sudden expansion, was investigated using a laser-Doppler velocimeter. Detailed measurements of mean axial velocities were made. Sets of partial differential equations—including continuity, axial and transverse momentum, turbulence energy, and turbulence dissipation—were simultaneously solved using finite differencing techniques. Predictions made using these equations were brought into good agreement with the data taken from the recirculating flows under investigation by selection of appropriate “constants” in the models.