Counter-flow phenomena studied by nuclear magnetic resonance (NMR) velocimetry and flow simulations

Abstract

Flow patterns including counter-flow and flow reversal effects have been studied by a combination of nuclear magnetic resonance flow imaging and numerical modeling using the finite volume method in the open-source computational fluid mechanics package OpenFOAM. Two cylindrical geometries have been used: In a concentric double-cylinder system the flow reversal under oscillatory rotation of the inner cylinder has been followed, and the time evolution of the flow reversal has been studied. We find extended periods of counter-rotating flow in the gap where fluid in the inner part of the gap follows the new direction of the rotor, while the outer part takes a longer time until the viscous forces transmit the reverted flow direction outwards. The radial position of the reversal of flow direction has been monitored as a function of the oscillation angle after the turning point. In the second cylindrical geometry, the rotating bob is placed off the center and a counter-rotating vortex is detected in the wider part of the gap. At constant viscosity and eccentricity, the position of the center of the vortex was found to depend on the rotation frequency of the bob. Qualitative and quantitative agreement between experiment and laminar (nonturbulent) flow simulations has been obtained for both steady-state flow using the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm and time-dependent flow using the Pressure Implicit with Splitting of Operators (PISO) algorithm.

Rheo‐NMR Spectroscopy for Cryogenic‐Probe‐Equipped NMR Instruments to Monitor Protein Aggregation

“…Because shear flow induces protein aggregation, Rheo-NMR makes it possible to observe aggregation-related structural changes of proteins at atomic resolution and in real time. In addition, through the use of magnetic resonance imaging and pulsed-field gradient NMR techniques, Rheo-NMR can be utilized to directly visualize flow patterns in the sample cell by determining the vector velocity of water (Kohn, Walinda, Sugase, Morimoto, & Scheler, 2022) Step 1. Inserting the sample into the NMR instrument 1.…”

“…Although the glass stick of the flexible rod is designed to be ideally aligned with respect to the NMR tube, any unexpected misalignment can cause undesirable secondary flow patterns to emerge (Kohn et al, 2022) or potentially break the tube or stick.…”

Rheo-NMR at the Phase Transition of Liquid Crystalline Poly-γ-benzyl-l-glutamate: Phase Kinetics and a Valuable Tool for the Measurement of Residual Dipolar Couplings

“…Rheo-NMR is a well-established technique that allows revealing detailed properties of viscous liquids – and liquid crystalline phases (LCs) under applied shear. – Particularly the combination of rheo-NMR and deuterium NMR with the residual quadrupolar coupling of deuterated solvents provides a highly sensitive measure for alignment properties of LCs and has been used extensively. – Experiments, however, are usually performed in a steady rheological state using specialized NMR-probehead that show excellent distribution of shear forces but compromised sensitivity and shim. ,, A better setup for our intended applications adds the rheology in a modular way . Not long ago, the Scheler group developed an apparatus for use with a conventional 5 mm high-resolution NMR probehead to study the effect of shear forces on a protein in solution with the highest currently available sensitivity. – The modular and relatively simple apparatus has led to important novel insights, but applicable shear forces are limited by the weak built-in sample spinning capabilities of the NMR spectrometer and only allow steady-state rheological conditions.…”