Molecular Dynamics Investigation of the Mechanism of Turbulence Modification by Polymer Additives and Noise Irradiation

摘要

Molecular dynamics computer simulation experiments have been carried out to study the response of a dilute short-chain polymer solution subjected to severe flow conditions. Under high amplitude shear flows the polymer molecules were observed to reorient and reconfigure so as to be confined to a plane parallel to the flow direction. Once this situation is achieved, aperiodic cycling between coiled and elongated forms within the plane was observed. No significant enhancement of the intramolecular oscillations was seen, nor was there any flow-induced tension developed in the molecule. Conversely, in a configuration in which one end of the molecule was anchored and a uniform flow of solvent was maintained, scission of an intramolecular bond was found at high solvent flow velocities. The mechanism of bond rupture arose from the flow-driven excitation of intramolecular vibrational modes of motion of the molecule, the steady-state tension arising from viscous drag on the molecule being much smaller than that required for bond scission. Analysis of the flow-induced vibrations leads to the conclusion that bond breaking occurs only when there is substantial excitation of the low frequency acoustical modes of the molecule. This mechanism should also be operative in the degradable of very long-chain polymers in a flow field characterized by an extesional velocity gradient.