Experimental study of laminar-to-turbulent transition in pipe flow

Abstract

This paper describes an experimental study of the unforced laminar-to-turbulent transition in pipe flow. Two pipes with different length-to-diameter ratios are investigated, and the transition phenomenon is studied using pressure measurements and visual observations. The entropy change and force balance are examined, and the peak powers are measured through fast Fourier transform analysis at various Reynolds numbers. Visual observations show that the flow structure changes at the Reynolds numbers corresponding to the peak powers. There is no clear dependency of the transition on the ratio of pipe length to diameter. The flow conditions are classified as laminar flow, transitions I, II, and III, and turbulent flow, separated by Reynolds numbers of approximately 1200, 2300, 7000, and 12 000, respectively. The transition at a Reynolds number of 1200 is caused by the force balance between the laminar and turbulent flows. The other transitions are related to the flow condition in the development region upstream of the pipe flow region. That is, the laminar-to-turbulent transition in the development region affects the transition condition in the downstream pipe flow. The laminar and turbulent development length ratios derived from the entropy changes are in reasonable agreement with the formulas for both laminar and turbulent flows. At large Reynolds numbers, the laminar flow condition will be established through the creation of a laminar-flow velocity profile at the entrance to the pipe.

Study of the reverse transition in pipe flow

“…In Pipe C, the factor decreased at approximately ReD=1600. In a previous study, the factor deceased between ReD=1200 and 12 000 [11]. Patel and Head reported that the coefficient deviated at ReD=1700 and returned at ReD=30000 [22].…”

“…The measured pressure was analysed using a fast Fourier transform, and a power peak appeared at ReD=1800 in the downstream pipe. In Pipe C and the ordinary pipe [11], the peak appeared at ReD=1200. The flow condition for the transition was different from that in ordinary pipe flow at low Reynolds numbers.…”

“…Patel and Head reported that the coefficient deviated at ReD=1700 and returned at ReD=30000 [22]. The decrease was caused by a change from laminar to turbulent flow in the transition [11]. In the downstream pipe, however, the friction factor decreased between ReD=4000 and 10000.…”

“…The flow from the divergent section was presumed to be a mixture of the average velocity profile flow from the reservoir and turbulent flow. The change in entropy was examined in a way similar to the study of the entropy change from reservoir to laminar or turbulent pipe flow in an ordinary pipe [11]. First, we examined the change from average velocity profile flow to reverse transitioned laminar flow.…”

Laminar Viscous Fluid Flow with Micro-rotation Capabilities through Cylindrical Surface

“…The movement of particles in the fluid forms a boundary layer due to friction between particles. The boundary layer divides fluid flow into laminar, transitional, and turbulent flow (Hattori et al, 2022). The regular and parallel movement of particles is called laminar flow (Committee, 2019).…”