Pulsed gradient spin echo nuclear magnetic resonance measurements of hydrodynamic instabilities with coherent structure: Taylor vortices

Pulsed gradient spin echo (PGSE) nuclear magnetic resonance (NMR) is applie d to the characterization of hydrodynamic instabilities. It is demonstrated theoretically and experimentally that for Taylor vortex flow in a Couette cell the PGSE NMR data is coherently modulated in an interference pattern d ependent upon the vortex size, or wavelength, and velocity intensity. Spati ally resolved NMR velocity images of all three velocity components for wate r in supercritical Taylor number flow and NMR velocity image data of the ax ial disturbance velocity for pentane at three supercritical values of the T aylor number are presented, For the short column used the NMR velocity data clearly show axial asymmetry with maximum velocities and the center (eye) of the vortex drawn toward the radial outflow boundary. (C) 1999 American I nstitute of Physics. [S1070-6631(99)01705-5].