Numerical Analysis of External Gear Pumps Including Cavitation

Abstract

Hydraulic machines are faced with increasingly severe performance requirements. The need to design smaller and more powerful machines rotating at higher speeds in order to provide increasing efficiencies has to face a major limitation: cavitation. The problem is inherently three-dimensional, due to the axial clearances, the relief and circumferential grooves, and to the circular pipes through which the fluid enters and exits the pump. A simplified two-dimensional numerical approach by means of computational fluid dynamics (CFD) has been developed for studying the effect of cavitation in the volumetric efficiency of external gear pumps. The assumptions employed prevent from predicting realistic values of the volumetric efficiency, but show to be valid to understand the complex flow patterns that take place inside the pump and to study the influence of cavitation on volumetric efficiency. A method for simulating the contact between solid boundaries by imposing changes in viscosity has been developed. Experiments of unsteady cavitation in water and oil performed by other authors have been numerically reproduced using different cavitation models in order to select the most appropriate one and to adjust its parameters. The influence of the rotational speed of the pump has been analyzed. Cavitation in the suction chamber very effectively damps the water hammer associated to the sudden change of the contact point position at the end of the gearing cycle. At high rotational speeds, the volume of air becomes more stable, reducing the flow irregularity. When cavitation takes place at the meshing region downstream from the contact point, the volume of air that appears acts as a virtual second contact point, increasing the volumetric efficiency of the pump.

Analysis of a scroll machine for micro ORC applications by means of a RE/CFD methodology

“…[18] the attention was given to the turbulence structure in the suction chamber, while in Ref. [19] the analysis referred to the pressure variation and cavitation phenomena. In these cases, the 2D strategy allows the comprehension of the major fluid dynamic phenomena involved in volumetric devices.…”

Three-Dimensional Numerical Analysis of an Operating Helical Rotor Pump at High Speeds and High Pressures including Cavitation

“…Besides it can produce pressure fluctuations and noise, it also has effect on volumetric efficiencies [4][5][6][7].Along with the cavitation, the problems of two-phase flow appear, which have significant influences on work performance of gear pumps [8]. Numerical simulation of an external gear pumps operating at speeds below 3000rpm including cavitation is studied by D. del Campo [4], who discusses the influences on the volumetric efficiency under different rotational speeds. In order to understand the complex fluid dynamic characterization, Zhou et al [9] simulate 2D gear pumps running at high pressures and high speeds, but cavitation is not considered.…”

Lumped Parameter Modelling of Cavitating Orifice Flow in Hydraulic Systems

“…Particularly, due to the upstream side connecting to the oil reservoir, hydraulic orifices or restrictions in the supply system of open circuits, cavitation may be more easily induced [3]. In other cases, the large pressure drop produced by the narrow flow restrictions in hydraulic control valves or the insufficient flow in high-speed rotating hydraulic pumps also indicates a strong tendency of gaseous cavitation [4] and [5]. Nowadays, the bigger pressure ratio or higher shaft speed required by the increasing power density of systems brings a significant challenge to the modelling and designing on the new generation of hydraulic components.…”

“…In order to calibrate empirical coefficients in the CFD gaseous cavitation model, three parameter sets are carefully chosen based on the experience of previous research including Set A proposed by Zwart et al [8], Set B proposed by Campo et al [5] and Set C provided by the authors. All the values are shown in Table 2.…”

“…Typical examples are given by the models by Singhal et al [7] (also known as the "full cavitation model"), Zwart et al [8] and Schnerr and Sauer [9], which are already implemented in commercial software such as ANSYS Fluent [10]. However, these models are very limited to simulate fluid power systems or complex pumps since many aspects which have a substantial impact on the unit performance are neglected, as done in the literature [5] and [11]. For this reason, the lumped parameter (LP) approach is often employed in fluid power research because it is effective, quick as well as robust for studying the dynamic features of hydraulic systems.…”