Characterization of accelerating pipe flow

Paul John Lefebvre, University of Rhode Island

Abstract

A unique series of experiments was conducted to determine the effects of constant acceleration on the flow in a 5-cm diameter pipe. These experiments, which differed substantially from those of previous researchers, investigated such phenomena as transition to turbulence and the general physics of the effect acceleration has on various flow parameters such as wall shear stress, velocity profile, and turbulence intensity profile.^ To conduct the experiments of the present study, a new transient flow loop was designed and built. This facility provided the capability of programmed acceleration via a control system that used the position of a downstream control valve for transient flow control. The repeatibility of the facility was established to be $\pm$0.5.^ A total of 1016 transient runs were conducted at constant acceleration between 1.8 and 11.8 m/s$\sp2$ over a large velocity range up to 11.3 m/s. Accelerations were either started from rest or from an initially turbulent flow at a mean velocity of 1 m/s. For the runs from rest, the flow remained laminar up to transition pipe Reynolds numbers ranging from 2 $\times$ 10$\sp{+5}$ to 5.2 $\times$ 10$\sp{+5},$ depending on the acceleration. Transition essentially occurred at the same instant over the length of the pipe indicating global transition. Two parameters that were approximately grouping K$\sb{\rm a}$, whose mean value is 1.53 $\times$ 10$\sp{-8}$, and the local boundary layer thickness parameter Re$\sb{\delta}$, whose mean value is 24,300.^ Prior to transition, the velocity profile agrees with that calculated using Szymanski's exact solution for a suddenly applied constant pressure gradient. For low accelerations, the wall shear stress can also be calculated using Szymanski's solution. But for high accelerations, wall shear stress remains constant over a very large velocity range. Following transition, wall shear stress, velocity profile, and turbulence intensity profile all follow the quasi-steady turbulent values. At transition, the wall shear stress and the velocity profile change to the quasi-steady values almost instantaneously (generally within 0.017 seconds). For the tests conducted from an initially turbulent flow, no relaminarization was observed. However, the flow did tend to be somewhat stabilized. ^

Subject Area

Engineering, Mechanical

Recommended Citation

Paul John Lefebvre, "Characterization of accelerating pipe flow" (1987). Dissertations and Master's Theses (Campus Access). Paper AAI8811562.
http://digitalcommons.uri.edu/dissertations/AAI8811562

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