Title

Detailed measurements of accelerating-flow properties in pipes

Document Type

Conference Proceeding

Date of Original Version

12-1-1992

Abstract

As part of a continuing study of accelerating laminar-transitional-turbulent flow in pipes, extensive measurements have been made of unsteady velocity profiles, wall pressure, pressure gradient, wall shear stress, and turbulence intensity distributions. Accelerations were approximately constant and begun either from rest or from an initially turbulent flow. For acceleration from rest, the instantaneous velocity profiles are in reasonable agreement with classical laminar-flow theory for a suddenly imposed pressure gradient. However, shear stress is not in agreement, and the cause is found to be a brief but large transient in the pump-driven pressure gradient. Numerical solutions for varying pressure gradient improve the prediction of wall shear stress. After a rapid (30 ms) transition period, the turbulent flow data are in good agreement with classical correlations for mean velocity and turbulence intensity. For acceleration starting from an initially turbulent condition ReD ≈ 50,000, the flow remains turbulent, with a moderate initial decrease in turbulence intensity and wall shear stress. The flow then returns approximately to quasi-steady conditions.

Publication Title

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED

Volume

139

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