Control of Transition to Turbulence in Constant-Acceleration Square Duct Flow

Abstract

A constant acceleration flow is generated in a square duct using a butterfly valve driven by a stepping motor. The valve is opened at programmed rotation speeds until the opening area attains a predetermined value. The acceleration of flow therefore changes suddenly from a constant non-zero value to zero. Transition to turbulence occurs when an instantaneous Reynolds number is raised above a certain critical value. This critical Reynolds number depends on the acceleration and becomes greater than the steady flow value of approximately 3000 with an increase in the acceleration. It is possible to delay the transition to turbulence by changing the final opening area. The period from the start of 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.