Transition to Turbulence in Constant Velocity Pipe Flow after Initial Constant-Acceleration

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Unsteady pipe flows such as oscillating flow, pulsating flow, and transient flow are frequently encountered in engineering fields. Significant effort has been devoted to understanding the basic characteristics of these flows. Experimental and theoretical studies of transition to turbulence, however, are rather limited and restricted to simple constant-acceleration pipe flows and pulsating pipe flows. Information on the transition to turbulence in flows with complex histories is not available. In this study attention is focused on an air flow in a pipe subjected to an initial constant-acceleration followed by an almost instantaneous switch to a constant-velocity condition. The final Reynolds number based on the constant velocity is greater than the critical Reynolds number for steady pipe flow. The time from the start of the constant velocity flow to the initiation of turbulence can be predicted by an empirical equation. This equation is derived in this study by taking the burst period into consideration. Information on this flow provides a better understanding of the effect of initial acceleration on the transition to turbulence
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