Currently the cavitation erosion damage becomes a critical issue that limits the centrifugal pump life cycle extension. Despite of a long history of studying the cavitation erosion phenomenon in centrifugal pumps there are still no reliable assessment methods except semi-empirical formula having rather limited application and accuracy. The paper is presenting a novel method for assessment of centrifugal pump cavitation erosion combining 3D unsteady flow CFD modeling and numerical analysis of cavitation bubbles behavior. The Navier-Stokes equations are solved by a splitting method with the implicit algorithm and high-order numerical scheme for convective transfer terms. The 3D numerical procedure is based on non-staggered Cartesian grid with adaptive local refinement and a sub-grid geometry resolution method for description of curvilinear complex boundaries like blade surfaces. Rotation is accounted with implementation of “sliding-grid” technology. The method considers evolution of the bubble in 3D flow from initial conditions until the disruption moment with determination of the erosion jet power impact. Validation of the method on model feed centrifugal pump stages is completed for two model centrifugal impellers Centrifugal impeller #1 is designed with a goal of through-passed shaft pump flow modeling. There are completed computations of cavitating bubbles’ evolution under non-uniform pressure field that show the non-uniform pressure distribution near the blade surface causes an essential influence on cavitation erosion. Computational prediction of the impeller #1 cavitation erosion damage is confirmed experimentally.

CFD analysis of two first-stage centrifugal impellers is undertaken with the main goal to obtain additional evaluation data regarding flow characteristics of the old first stage impeller design and in the proposed new cantilever impeller design. The new design is developed to reduce the 1st stage impeller cavitation erosion damage of a multistage centrifugal feed pump. This stage of work comprises computational tests of both impeller models under the same mode of operation, 3000 RPM and volumetric flow rate 0.0503 m3/s. Both impellers are planning to be tested experimentally. The inlet geometry for CFD tests is taken from the test facility draft. The outlet is made like a circular vaneless diffuser. In the old design, a hub developed upstream presents the through shaft. Computational results are compared with the head/efficiency data delivered by plane cascade theory. Computational data shows an advantage of the new design by head and efficiency although the efficiency level is underestimated. Computational data shows lower pressure zones in the proposed design are localized at the impeller inlet periphery, in the old design lower pressure zones spreads along the blade inlet height. Further computational test will be made for the whole geometry including the stage stator part and experimental validation of the proposed design will follow.

Information about cavitation characteristics of centrifugal pumps and critical cavitation conditions is given. Depending on the position of the leading edge, impellers are divided into three groups. The spatial lattice of the impeller is presented as a set of elementary lattices on the axisymmetric surfaces of a current of equal-velocity meridional flow. Equations have been derived from the determination of the cavitation margin and the equation of the energy in relative motion for the critical cavitation margin containing a cavitation coefficient referred to the impeller inlet. General equations have been obtained for the critical cavitaion coefficient of specific speed, which can be used to analyze the influence of geometric and operating conditions on the suction capacity of centrifugal impellers, which must be taken into account in designing them. The selection of the typical inlet diameter of the impeller has been substantiated and the critical cavitation coefficients of the elementary lattices have been found. An empirical equation, valid in the whole range of parameters encountered in practice, has been derived for the cavitation coefficient of type-3 impellers with a leading edge located roughly on the diameter of the impeller neck. An analytical equation, applicable for type-1 and -2 impellers, is given for the critical cavitation coefficient with empirical force coefficient values. A scheme for calculation of the suction capacity of such impellers is presented.We shall examine the cavitation characteristic of a pump, which depicts the dependence of the head and power consumption on the cavitation margin at the pump inlet at a constant rotation speed n and a delivery Q of the pump:where p in is the absolute pressure at the inlet, p sv is the absolute saturated vapor pressure, ρ is the liquid density at the inlet, and v in is the mean liquid velocity at the inlet.Several critical cavitation conditions are discernible in the cavitation characteristic. The first (I) critical condition corresponds to the beginning of change in the head or power and the second (II), to the beginning of dramatic change in the head and power. When a vane pump operates with a single-component liquid not containing undissolved gases as impurities, in the densely spaced lattices of the impeller vanes cavities (pockets) form under these conditions and they join up on the vanes, forming eddies. According to the published data [1][2][3][4], the length of a cavity under the second critical condition is roughly equal to the pitch of the vane at the impeller inlet. The eddy trails past the cavities are washed out by the main flow before exiting from the impeller and, consequently, do not affect the flow kinematics at its outlet. So, the head and power under the second critical condition change little compared to those under cavitation-free conditions. Under this condition, the pump sucks and discharges the liquid, i.e., it retains the operating capacity. Upon subsequent small diminution of the cav-

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