Estimation of Magnitudes of a Static and Dynamic Axial Thrust Acting on the Impeller by Applying the Mathematical Model Approach to a Flow through Hydraulic Passages of the Hydromachine with Account for a Flow through Auxiliary Channels

Abstract

More stringent reliability requirements placed upon pump operation call for a more accurate prediction of integral characteristics of a machine at the design stage, including estimation of hydrodynamic forces. The existing analytical techniques for estimation of the magnitudes of the axial thrust acting on the pump impeller are based on the assumptions that fail to account for an actual flow pattern in sidewall gaps and for geometry of the sidewall gaps, static pressure distribution at the impeller outlet, and for unsteady processes which occur both during operation close to the optimum flow rate and during off-design operation of the pump. At present, the method which implies numerical modeling of a flow through hydraulic passages of the hydromachine is gaining ever greater importance for investigation of features of a flow pattern under different operational duties, and also for estimation of any integral characteristics including axial thrust. The present paper gives an overview of joint researches done by specialists of VNIIAEN JSC and masters of Applied Fluid Mechanics Chair of Sumy State University with regard to estimation of magnitudes of steady and unsteady components of the axial thrust for pumps of various construction types. The flow through hydraulic passages was modeled by employing a numerical solution to a system of Reynolds equations and the continuity equation. The standard k-ε turbulence model was used to close the system of equations. The modeling was performed both under steady and unsteady conditions for a viscous incompressible medium. As a result of the investigation, magnitudes of steady and unsteady components of the axial thrust were estimated for a double-entry impeller under the following duties: optimum flow rate and 0.5Q_opt, as well as for a mixed-flow impeller with balance holes on its rear shroud. The paper provides results of comparison of axial thrust magnitudes which were obtained numerically and analytically.