It is known that the presence of liquids can significantly affect the dynamic motions of immersed solids. This paper proposes a method for evaluating fluid forces for use in the dynamic analysis of moving systems in which solid bodies are completely immersed in incompressible, frictionless fluids. A damping parameter is suggested to determine whether a fluid system may be considered frictionless. The incompressibility requirement is also discussed. Experimental data are cited to support the proposed method. Formulas for hydrodynamic masses are tabulated.

Analysis and tests were made to investigate the hydrodynamic mass and damping effects of a liquid in a thin annulus surrounding a vibrating rotor. The analytical results are described in this report and the test results in Part 2. The analysis determines the fluid forces for the general case of a vibrating rotor. Vibrational amplitudes and the limits of dynamic stability are then determined for a constant-speed rotor excited by unbalance. Fluid flow was assumed incompressible and tangential and to be in the Taylor vortex regime or in the turbulent regime. The Taylor vortex regime is considered a natural convection process resulting from centrifugal force gradients, while the turbulent regime is a forced convection process. As a result, annular flow around a rotor is considered an inherent combination of forced and natural convection. Fluid damping is estimated for each process separately and for the case where the vortex and turbulent process are predicted to occur simultaneously.

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Analyses and tests were made to investigate the hydrodynamic mass and damping of a fluid in a thin annulus surrounding a rotor which is vibrating due to unbalance forces. The analysis is described in Part 1. This report describes the tests. Vibrational amplitudes were measured of a constant-speed rotor with various fluids and radius-to-clearance ratios. Axial flow was restricted by limited-leakage end seals. The fluid flow was considered to be either vortex or turbulent, based on the Taylor or Reynolds number. The presence of the fluid was found to lower the critical speed. This effect was ascribed to a hydrodynamic mass which was evaluated from the tests. Hydrodynamic masses were also determined for the rotor vibrating without rotation and were found to be in agreement with the results of Stokes [1]. All results were in reasonable agreement with the predictions of Part 1.

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