SINGLE-PHASE IMPINGING STREAMS

This chapter discusses the theory of laminar and turbulent impinging streams (IS), together with experimental observations and some applications of single-phase IS. In 1960, Powell proposed a theoretical model that can be used as a first step in understanding the number of the various flow modules associated with the IS flow field. According to Powell's mirror image concept, the impingement of two jets separated by a distance L is equivalent to the impingement of one of the jets on a flat plate placed at a distance L/2 downstream. According to Nosseir, while the mirror image concept is plausible if the impinging jets are laminar, its validity is doubtful in turbulent colliding jets. An experimental study on the characteristics of the flow field in IS revealed that pressure fluctuations were generated at the impingement plane of the streams, which were amplified by a feedback mechanism. Champion and Libby, Kostiuk and Libby, and Kostiuk and others were probably the first to present a theory of turbulent IS. Their model was verified with reasonable accuracy by measurements of the mean axial velocity and the intensities of the axial and radial velocity components.