The 2019 MRV challenge: turbulent flow through a U-bend

While magnetic resonance velocimetry (MRV) has been used in technological flow studies for over 30 years, it has not yet reached the levels of usage as more traditional experimental techniques such as particle image velocimetry or laser Doppler anemometry. This work involves a relatively simple U-bend geometry with complex three-dimensional turbulent flow characteristics which was shared with four research groups, including a combined effort from the U.S. Military Academy/Stanford University, and teams from Hanyang University, the University of Rostock, and the Mayo Clinic. The geometry—including upstream flow development—was shipped between groups with nominally similar experimental conditions, and the acquired data are presented including both two- and three-dimensional comparisons. In addition, details on how each team conducted the MRV experiments are provided, with each team using a different set of procedures and hardware. The results are remarkably similar, with only a few variations at the flow regions with the highest in-plane velocity gradients showing differences outside the combined uncertainty of the results. Graphic abstract