Run-up Simulation of Automatic Balanced Rotors Considering Velocity-dependent Drag Coefficients

Abstract

The paper at hand presents the modelling approach of a laboratory centrifuge with a vertically mounted rotor and an automatic balancing device, which counterbalances the unbalance in one plane. This device consists of an annulus containing the outer ring of a ball-bearing as well as steel balls and is filled with a newtonian fluid. The fluid, accelerated by the annulus’ walls, flows around the balls and positions them in the annulus. In order to develop a design method for the balancing device the velocity dependency of the drag coefficient is considered and the influence of fluid density and viscosity on the balancing efficiency is examined. An experimental comparison shows that the flow in the concave bearing race can be represented by the flow around a ball in contact with a flat surface. It can be shown that, depending on the run-up acceleration, a selective choice of the fluid properties has a positive influence on the vibrations near the critical speed and the response time of the counterbalancing effect at supercritical speeds.