Three-dimensional concentration field measurements in a mixing layer using magnetic resonance imaging

Abstract

Magnetic resonance imaging (MRI) was used to measure the three-dimensional, time-averaged concen- tration distribution in a turbulent two-stream mixing layer. Test fluids and MRI scanning parameters were chosen to give good signal linearity, and a calibration/normalization procedure was developed to reduce the concentration measurement uncertainty. Plain deionized water mixing with a solution of 0.8% gadopentetate dimeglumine in deionized water were selected as test fluids. The concen- tration of the marked water was measured on an array of 220,000 0.69 mm 3 voxels covering the entire flow appa- ratus. Planar laser-induced fluorescence experiments were performed on the flow centerplane to provide validation data. The uncertainty of a single voxel measurement was estimated to be less than 12% with the largest source of uncertainty being turbulent dephasing. Averaging two runs in which the marked water was switched between the two streams reduced the uncertainty to only 4%. The complete magnetic resonance concentration (MRC) procedure including the adjustment of scanning parameters, a back- ground run, two reference/calibration runs, and multiple concentration measurement runs can be completed in 2- 3 h. This work establishes MRC as a viable technique for studying the mixing in complex turbulent liquid flows.