Abstract: We investigate experimentally the turbulent flow through a two-dimensional contraction. Using a water tunnel with an active grid we generate turbulence at Taylor microscale Reynolds number Re_lambda ~ 250 which is advected through a 2.5:1 contraction. Volumetric and time-resolved Tomo-PIV and Shake-The-Box velocity measurements are used to characterize the evolution of coherent vortical structures at three streamwise locations upstream of, and within the contraction. We confirm the conceptual picture of coherent large-scale vortices being stretched and aligned with the mean rate of strain. This alignment of the vortices with the tunnel centerline is stronger compared to the alignment of vorticity with the large-scale strain observed in numerical simulations of homogeneous turbulence. We judge this by the peak probability magnitudes of these alignments. This result is robust and independent of the grid rotation protocols. On the other hand, while the point-wise vorticity vector also, to a lesser extent, aligns with the mean strain, it principally remains aligned with the intermediate eigenvector of the local instantaneous strain-rate tensor, as is known in other turbulent flows. These results persist when the distance from the grid to the entrance of the contraction is doubled, showing that modest transverse inhomogeneities do not significantly affect these vortical-orientation results.
Biography: Vivek is a PhD candidate in the Mechanical Engineering (ME) Program, PSE Division. He joined the High Speed Fluids Imaging Laboratory in 2015. He earned his bachelor’s degree in ME from Anna University Chennai, India in 2006; and master’s degree in Thermal and Fluids Engineering from Indian Institute of Technology Bombay (IITB), India in 2010. After completion of master’s, he worked as a faculty in the ME department at Amrita University Coimbatore, India. His current research is focused on tomographic measurements of turbulent flows.