Experimental observations on transition to turbulence in confined coaxial jets and other boundary layer flows
Experiments were performed to demonstrate the transition to turbulent flow of water jets discharging coaxially into a stream confined in a round duct. Experimental apparatus consisted of a storage tank, pump, constant head tank to minimize pump transients, and two lines of different diameter. Valves were used to control flow rates through both lines. The critical Reynolds number is shown to be a strong function of velocity ratio. Flow visualization showed a proportionality between the laminar length of the jet and the wavelength. This coincides with similar observations concerning the transition to turbulence in various other flows. A brief argument based on scale analysis for the confined coaxial jet and round plume is presented. The apparent universality of the scaling law supports the conclusion that the laminar sections of all naturally progressing boundary layer-type flows are geometrically similar. (from authors' abstract)
