CALCULATION OF MINIMUM CRITICAL REYNOLDS NUMBER FOR LAMINAR-TURBULENT TRANSITION IN PIPE FLOWS

This article describes the calculation of the minimum critical Reynolds number for laminar-turbulent transition in pipe flows. From the conclusions of our previous experimental study, it is clear that a transition occurs near the pipe inlet and the critical Reynolds number R(c) takes the minimum value of about 2000 in the case of a straight pipe. Moreover, in our previous calculations of laminar entrance pipe flow, it was found that near the pipe inlet a large pressure gradient in the radial direction exists, which decreases as the Reynolds number Re increases. Thus, we have built a new transition macromodel to determine R(c) using the effect of the radial pressure gradient. The calculated results were R(c)(min) = 3750 when the number of radial grid points J0 = 51 and 2200 when J0 = 101.