Research Multiphase and index-matched flows
Turbulence in round pipes across area changes
Stereo and tomographic PIV of turbulent pipe flow through abrupt and gradual expansions and contractions, a simple geometry that is notoriously hard to image.
High-resolution stereo PIV experiments are performed in the refractive-index-matched round channel with varying pipe geometries. We study the flow near an abrupt expansion or contraction to understand how the area change affects the turbulence upstream and downstream of the step. Four cases, with 45° and 90° steps in both directions, are compared at matched inlet Reynolds number; the area ratio is 2.56:1 for the contractions and 1:2.56 for the expansions. Although this is a simple problem, it is extremely difficult to image because of the curvature of the pipe, a difficulty that refractive index matching removes.
From the PIV data we characterize the recirculation region behind the step, the shear layer and the turbulent stresses. Pressures and flow rates are chosen to prevent cavitation. Comparing the turbulence characteristics of the different expansion and contraction regions helps explain pressure losses, sedimentation in particle-laden flow and efficiency. Reduced-order modeling with proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) isolates the important features of the flow field, and the stereo PIV results are extended with high-speed tomographic PIV and time-resolved stereo PIV.
