Transition to Turbulence and Velocity Distribution in an Oscillating Pipe Flow

Abstract

Experiments on transition to turbulence in an oscillating pipe flow were made by using a hot wire anemometer over ranges of Reynolds numbers R_{e os} = |μ_{m, os, l}| D/ν(|μ_{m, os, l}|is the cross-sectional mean velocity amplitude, D = 2R the pipe diameter, ν the kinematic viscosity) from 600 to 65000 and of dimensionless frequencies √(ω') = R√(ω/ν) (ω is the angular frequency) from 2.6 to 41. Critical Reynolds numbers from laminar to transitional and from transitional to turbulent flows agreed well with published experimental results. In the turbulent regime turbulent bursts follow by relaminarization in the same cycle. It is observed that the instantaneous velocity profile in every phase when a turbulence with higher frequency appears is represented by the well-known Blasius 1/7 power law, but in the laminar-like phase it does not follow the laminar theoretical solutions for a steady oscillating pipe flow.