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 //o//s equals vertical u//m//,//o//s//,//l vertical D/ upsilon ( vertical u//m//,//o//s//,//l vertical is the cross-sectional mean velocity amplitude, D equals 2R the pipe diameter, upsilon the kinematic viscosity) from 600 to 65,000 and of dimensionless frequencies ROOT omega prime equals R ROOT omega / upsilon ( omega 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 are followed 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.