MRV challenge 2: phase locked turbulent measurements in a roughness array

Magnetic resonance velocimetry (MRV) provides capabilities to measure three velocity components across three-dimensional fields of view without the need for optical accessibility. Predominant usage of the technique in engineering applications centers on steady flows and the discussion of a single time-averaged set of data. In this second MRV Challenge comparison, phase-locked MRV measurements of a pulsatile flow are conducted by five teams from across the globe. A geometry is explored which consists of turbulent flow past six identical cubic elements placed in the center of a square water channel, with partial elements along each side of periodically varying heights. A pulsatile injection flow through the floor between the second and third cubic roughness elements creates a three-dimensional jet that interacts with the complex cube wakes. The details of each scan sequence are summarized for the teams. Results are compared for three different time windows—one pre-injection, a second while the injection flow accelerates, and a third during a quasi-steady condition with the injector fully on. Finally, the influence of the temporal resolution selection for the phase locked MRV is discussed. The results are remarkably similar despite the complex flow configuration selection and showcase a relatively underutilized capability to obtain time-dependent, volumetric data for periodic flows through three-dimensional geometries using MRI. Recommendations for best practices are also provided.