Drag on object moving through foam

Abstract

<p>Foams consist of small gas bubbles separated by thin liquid films. Although many complex models have been developed to describe the rheological properties of foam, very little information is available concerning the flow charateristics of foam flowing past an object. The purpose of this research was to investigate foam flow properties by performing simple experiments to determine the drag charateristics of simple-shaped bodies moving through foam;A rotating tank apparatus was built and used as the equivalent of a wind tunnel in aerodynamic testing. Foam with consistent properties was produced and models of various shapes were suspended in the moving foam. The drag on the model moving through the foam was obtained by using a simple strain gauge force balance. The foams were made from liquid soap, water, and air. By varying the percent of these quantities, foams with various properties were produced;The drag was measured as a function of velocity, foam properties, and body type (spheres, disks, ellipsoids, and flat plates). Various surface roughnesses were tested to determine the dependence of drag on surface texture. This is especially important for foam flows because of their "slip" condition at solid surfaces;The experimental data obtained indicate that a foam flow has a Bingham plastic charateristic with a yield stress. The drag was a consistent function of the foam quality and soap-water solution's viscosity. For the case of rough surface specimens, the drag increment differs from that of Newtonian laminar flow.</p>