Turbulence in round pipe flow across change in cross-sectional area
High resolution Stereo-PIV experiments are performed in the refractive index matched round channel, with varying pipe geometries. The flow in the vicinity of an abrupt expansion or contraction are studied to understand the effect of area expansion/contraction on the turbulence characteristics upstream and downstream of the step. Four cases, with 45 and 90 degree steps are used and the flow Reynolds number is matched at the inlet. The area ratios are 2.56:1 for contraction and 1:2.56 for expansion cases.
The characteristics of the recirculation region behind the step, the shear layer and turbulent stresses are estimated from the PIV data. The pressures and flow rates are chosen so as to prevent effects of cavitation. The turbulence characteristics of the various expansion/contraction regions are compared and can help understand the pressure loses, sedimentation in the case of particulate flow, efficiency etc. Reduced order modeling using Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) help capture the important features in the flow field. The results from the stereo-PIV studies are further extended and supplemented using high speed Tomographic-PIV and time resolved stereo PIV experimenst