The Effect of Impeller Cutback on the Fluid-Dynamic Pulsations and Load at the Blade-Passing Frequency in a Centrifugal Pump

Abstract

A study is presented on the fluid-dynamic pulsations and the corresponding dynamic forces generated in a centrifugal pump with single suction and vaneless volute due to blade-volute interaction. Four impellers with different outlet diameters, obtained from progressive cutbacks (trimmings) of the greatest one, were successively considered in the test pump, so that the radial gap between the impeller and the volute ranged from 8.8% to 23.2% of the impeller radius. The study was based on the numerical computation of the unsteady flow through the machine for a number of flow rates by means of the FLUENT code, solving the 3D unsteady Reynolds-averaged Navier–Stokes equations. Additionally, an experimental series of tests was conducted for the pump with one of the impellers, in order to obtain pressure fluctuation data along the volute front wall that allowed contrasting the numerical predictions. The data collected from the numerical computations were used to estimate the dynamic radial forces and torque at the blade-passing frequency, as a function of flow rate and blade-tongue radial gap. As expected, for a given impeller diameter, the dynamic load increases for off-design conditions, especially for the low range of flow rates, whereas the progressive reduction of the impeller-tongue gap brings about corresponding increments in dynamic load. In particular, varying the blade-tongue gap within the limits of this study resulted in multiplying the maximum magnitude of the blade-passing frequency radial force by a factor of about 4 for low flow rates (i.e., below the nominal flow rate) and 3 for high flow rates.

Numerical analysis of the unsteady flow in the near-tongue region in a volute-type centrifugal pump for different operating points

“…Following previous work by the authors [18], this paper presents a numerical study on the pulsating flow at the tongue region for a conventional centrifugal pump with a non-dimensional specific speed of 0.47 and an impeller-tongue gap of 11.4% of the impeller radius. The study focuses on the relation between the pressure pulsations and the fluctuating velocity field.…”

Energy Performance and Radial Force of a Mixed-Flow Pump with Symmetrical and Unsymmetrical Tip Clearances

“…Suzuki et al [20] examined the characteristics of the rotor-dynamic fluid forces on the impeller, measured rotor-dynamic fluid forces in cases with and without whirling motion, and found that the rotor-dynamic forces become destabilizing in a wide range of positive whirls. Barrio et al [21,22] studied the fluid-dynamic pulsations and the corresponding dynamic forces generated in a centrifugal pump with different outlet diameters due to blade volute interaction. They also estimated the dynamic radial forces and torque at the blade-passing frequency as a function of flow rate and blade-tongue radial gap, and determined that the dynamic load increased for off-design conditions.…”

Effects of Impeller Diameter on High-Speed Rescue Pump

“…Jain et al [24] proposed an empirical correlation to predict the efficiency of pump impellers that run in turbine mode. Barrio et al [25] compared the effects of four impeller diameter sizes on pressure pulsation.Šavar et al [26] proposed a maximum diameter trim value for pumps operating under a certain law. Wang and Liu [27] diameters.…”