Tomographic PIV measurements and RANS simulations of secondary flows inside a horizontally positioned helically coiled tube

Helically coiled tubes are widely used in industry to enhance heat and mass transfer in the laminar flow regime, due to their secondary flow pattern. In this study, tomographic particle image velocimetry (tomo-PIV) is used in a horizontally coiled helical tube to systematically acquire 3C-3D velocity fields for Reynolds numbers ranging from 20 to 1400 and Dean numbers from 8 to 567. The velocity field evaluations are performed using two different approaches: time-averaged velocity field calculation from instantaneous velocity fields and velocity field determination by cross-correlation from an ensemble of instantaneous reconstructed volumes. Equivalent velocity field accuracy is achieved in both velocity approaches when the flow can be considered stationary. Moreover, numerical simulations were carried out in the same geometry at the same flow conditions and were validated against the experimental 3C-3D data sets. The simulation results show good agreement with the measured velocities, offering the possibility of parametric studies and design optimization. To the authors’ best knowledge, this is the first systematic experimental investigation of a helical coil flow by means of 3C-3D velocity measurements, which results can now be used for validation of numerical models in computational fluid dynamics. Graphic abstract Measured time-averaged velocity visualized by vector-magnitude colour at horizontal and vertical slices (left) and Dean vortices detected by 3D Q-criterion (right) from the time-averaged measurements (purple isosurfaces) and from the simulation (red isosurfaces) inside the helically-coiled tube at Re = 220 and De = 89.