Studies on transition from laminar to turbulent flow in a pipe

Abstract

This thesis describes some investigations on the transition from laminar to turbulent flow in a straight pipe of circu lar cross-section. It is found that Emmons* Theory of transition by the formation and growth of turbulent spots can be extended to pipe flow. Mgiking the assumptions (whose, ju stifica tion is discussed) that the breakdowns occur at a single station downstream of the entrance, that the spot propagation is one dimensional as •plugs’ of turbulence which f i l l the pipe cross-section and grow in the axial direction, and that the mean flow is unaffected by the formation and growth of turbulent plu ^ a simple theory fo r the prediction of the intermittency factor and intermittency frequency is given. It is shown that measurements confirm the theory in a range of Reynolds Numbers just above the lower c r itic a l. At higher Reynolds Numbers, it was discovered that in pipes of su fficien t length a completely new situation develops in which the transition process is intimately associated with a mean flov; fluctuation. The non-stationary S U M M A R Y character of the mean flow and the formation and propagation of turbulence are highly interactive and lead to a sharp well defined frequency for turbulent plug production and mean flow fluctuation. In this range of Reynolds Numbers, the intermittency factor appears to lose much of its significance. Auxiliary experiments confirmed the mean flow time dependence and the dependence o f the frequency on flow parameters and pipe length was also investigated. The propagation rates for turbulence were measured fo r Reynolds Number range 2700 — 13000. A review of the existing theoretical and experimental information on the phenomenon of pipe flow transition precedes the main body of present investigations.