Particle Response to Low-Reynolds-Number Oscillation of a Fluid in Microgravity

Abstract

†§ This paper presents an experimental study of the response of a particle to the movement of a fluid in which it is suspended. The equations governing the motion of particles in the low Reynolds number regime have recently been solved analytically, and the solutions were used to design experiments to measure the most evasive term in the equation, known as the Basset history force. The objectives of the study are to compare experimental results with the solution to the particle equation of motion. Since the movement of a spherical particle in response to the surrounding fluid is predicted by the analytical solution to the theoretical equation of motion, the theory is tested by measuring the response of the particle to the fluid motion, specifically, the ratio of the particle to fluid displacement. In the experiment, particles are suspended in a fluid-filled cell, which is shaken in a carefully controlled oscillatory fashion. The particle and cell locations at the limits of motion are measured with great precision by applying electronic holography. Ground experiments were run with tethered particles to counteract gravity. The measured particle responses closely match the theoretical predictions for the full solution, and are clearly different from the solution where the history force is neglected. The results are important because they represent one of the first quantitative observations and analyses of the history force.