An approach of simulating journal bearings-gear pump system including components’ cavitation
Introduction
External gear pumps (EGPs) continue to be widely applied in aero-engines. The factors of success for this hydrostatic unit are reflected by its simplicity, efficiency and low cost. Following the hydrodynamic lubrication principle, the hydrodynamic journal bearing (HJB) is one of the key design units of EGPs. During the pump operation cycle, the gear shaft and bush are separated by a thin film between the shaft and HJB, which allows the shaft to rotate freely without metal-to-metal contact. Thus, the lubrication performance of HJBs is often one of the decisive factors in limiting the pump performance.
In rotodynamic pumps, cavitation is seen as an undesirable situation, which may cause many problems, such as noise, vibration, erosion and efficiency loss. To determine the hydraulic head loss of a pump, a well-known parameter, namely, the net positive suction head required (NPSHR), has been established [1] for several applications. An accurate numerical model of cavitating flows in rotodynamic pumps is essential. Over the years, several kinds of cavitation models have been proposed (Singhal et al. [2], Zwart et al. [3] and Schnerr et al. [4]) with application and validation [1,[5], [6], [7]]. In addition, the serious cavitation phenomenon in conformal contacts is also undesirable, which may cause an oil film oscillation [8]. While several studies regarding cavitation have been presented during the last decade, one of the major contributions came from Jakobsson, Floberg, and Olsson's published work [9,10]. Their theory, called JFO boundary, considers mass conservation on the film boundary and satisfies both accuracy and practicality; this theory has been widely used as a theoretical basis in cavitation numerical models. The most prominent studies of cavitation numerical modeling came from Elrod and Adams [11,12], who proposed the efficient numerical method for HJB cavitation. These models obeyed the physical laws of the JFO boundary and successfully embodied this theoretical improvement into the numerical simulation. The JFO-based mass-conserving cavitation algorithm shows its strong applicability, and examples of it can be found in [13], [14], [15], [16], [17] for journal bearings, in [18,19] for parallel bearings, in [20] for ring-liner conjunctions, in [21,22] for thrust bearings and in [23,24] for piston rings-liner.
Ideally, the shaft is widely considered parallel in bearing lubrication calculations. Nevertheless, this ideal situation rarely exists in rotation machines due to a multiplicity of factors, including manufacturing tolerances, installation errors and many elements during the operating cycle [25]. McKee et al. [26] made one of the first documented experimental observations that pointed out that the hydrodynamic pressure will be influenced by a misalignment; therefore, a misalignment bearing investigation is one of the subjects of experimental studies [27], [28], [29], [30]. In terms of numerical research, Vijayaraghavan and Keith presented the performance investigation of a grooved misaligned journal bearing considering cavitation [31,32]. Lahmar et al. [33] analyzed dynamically loaded engine main crankshaft bearings considering the misalignment effect. These researchers concluded that constant misalignment causes an obvious reduction in the film thickness, which should be considered carefully in bearing design. The static and dynamic characteristics were both investigated by Sharma et al. [34] considering the combined effect of misalignment and surface topography. Monmousseau and Fillon [35] studied the effects of misalignment on the static and dynamic characteristics of a tilting-pad journal bearing. These investigators pointed out that the bearing characteristics are directly related to the misalignment amplitude. Xu et al. [36] carried out a comprehensive analysis of the bearing performance with turbulent and thermo effects. Their study also indicated that misalignment may be detrimental to film generation. Jang and Khonsari [37] investigated the effect of wear on the bearing performance considering misalignment.
As one of the typical father components of journal bearings, the working principle of an external gear pump is uncomplicated: The fluid in the pump moves from the inlet to the outlet port during the gear rotating process, realizing fluid transfer. Due to the similar nature of the gear teeth, the gears stay at the same position at a certain angle. The flow pressure distribution varies periodically at a cycle in correspondence with the teeth number, which leads to periodic forces acting on the shaft. Subsequently, the periodic forces on the shaft cause changed shaft micromotion, film geometry, and lubrication characteristics. Regarding the EGPs in aero-engines, these forces have a high amplitude, which cannot be neglected in lubrication calculations. Thus, the lubrication problem of HJBs in an aero-engine EGP should be treated as a system-level problem. Castilla et al. [38,39] presented a novel method for journal bearing shaft movement in gear pumps with an experimental study. Pellegri et al. [40] established a computational fluid dynamics (CFD)-radial motion coupled model for EGP journal bearings, but their work did not consider the influence of cavitation. Du et al. [41] proposed a numerical analysis of journal bearing lubrication characteristics in a water hydraulic internal gear pump considering the effect of surface elastic deformation. To enhance the load support of the water film in the gap between the gear shaft and bush, Zhou et al. [42] investigated the influence of microshapes on gear pump journal bearings using an elastohydrodynamic model. Based on dynamic mesh techniques, Mo et al. [43,44] proposed a thermohydrodynamic calculation method for gear pump self-circulating bearings.
The simulation of the EGP-HJB system poses a major challenge because it involves a theory of different subjects, including lubrication, multiphase flow and rotodynamics. This paper presents an approach for solving this problem and details a methodology for solving the bearings lubrication problem and its coupling with the pump CFD model. Moreover, the cavitation models are integrated into the simulation framework to provide precise component cavitation analysis. This framework not only can be used to drive the designs of the lubrication and flow components but also allows a limitation in the pump conditions to avoid damage caused by severe wear or cavitation.
Section snippets
EGP-HJB simulation model details
A 3D model of the EGP-HJB system with a plane cross is depicted in Fig. 1, where the research components are highlighted. The input/output sample of the EGP-HJB simulation model can also be seen in Fig. 1. As represented in the figure, the proposed code has several main modules: the EGP CFD model, the film geometry model, the HJB lubrication model, and the model for the calculation of the gear shaft transient position and the geometrical model. To acquire precise results, the lubrication model
Results and discussion
In the current section, the results of the extensive sets of simulations for the HJB-EGP system are proposed. The specifications of the components are detailed in Table 1. Unless specified otherwise, these parameters are implemented in all simulations.
Conclusion
This paper presents a simulation framework to solve an engineering system-level problem for HJB-EGP based on lubrication and CFD simulation methods. As integrated submodels within this framework, different cavitation models are provided to enable an accurate representation of the cavitation in the system. The significant observations include the following:
- 1.
The results highlight the importance of the EGP influence on HJB lubrication. The maximum amplitude of the force fluctuation due to the gear
Funding
This work was supported by the National Science and Technology Major Project of China (grant no. 2017-V-0013-0065).
Declaration of Competing Interest
The authors declare that they have no conflict of interest.
References (51)
- et al.
A novel approach for predicting the operation of external gear pumps under cavitating conditions
Simul. Modell. Pract. Theory
(2014) - et al.
Mixed lubrication problems in the presence of textures: an efficient solution to the cavitation problem with consideration of roughness effects
Tribol. Int.
(2016) - et al.
Mass-conserving cavitation model for dynamical lubrication problems. Part II: numerical analysis
Math. Comput. Simul.
(2015) - et al.
Mass-conserving cavitation model for dynamical lubrication problems. Part I: mathematical analysis
Math. Comput. Simul.
(2015) - et al.
An experimental study of axial misalignment effect on seizure load of journal bearings
Tribol. Int.
(2019) - et al.
Effect of cavitation on the performance of a grooved misaligned journal bearing
Wear
(1989) - et al.
The effect of misalignment on performance characteristics of engine main crankshaft bearings
Eur. J. Mech. A. Solids
(2002) - et al.
On the wear of dynamically-loaded engine bearings with provision for misalignment and surface roughness
Tribol. Int.
(2020) - et al.
The numerical computation of turbulent flows
Comput. Meth. Appl. Mech. Eng.
(1974) - et al.
Influence of stochastic roughness on performance of a Rayleigh step bearing operating under Thermo-elastohydrodynamic lubrication considering shear flow factor
Tribol. Int.
(2019)
Mixed-lubrication analysis of misaligned bearing considering turbulence
Tribol. Int.
Demonstration and validation of a 3D CFD simulation tool predicting pump performance and cavitation for industrial applications
J. Fluids Eng.-Trans. Asme
Mathematical basis and validation of the full cavitation model
J. Fluids Eng.-Trans. Asme
A two-phase flow model for predicting cavitation dynamics
Physical and numerical modeling of unsteady cavitation dynamics
Comparison of computational results obtained from a homogeneous cavitation model with experimental investigations of three inducers
J. Fluids Eng.-Trans. Asme
Numerical analysis of external gear pumps including cavitation
J. Fluids Eng.-Trans. Asme
Oil film boundary analysis of spiral oil wedge sleeve bearing based on the dynamic loading conditions
Proc. Inst. Mech. Eng.Part J-J. Eng. Tribol.
The finite journal bearing considering vaporization
Trans. Chalmers Univ. Technol.
Cavitation in dynamically loaded bearings
Trans. Chalmers Univ. Technol.
A Cavitation Algorithm
J. Lubrication Technol.-Trans. ASME
A computer program for cavitation and starvation problems
A transient analysis of the textured journal bearing considering micro and macro cavitation during an engine cycle
Proc. Inst. Mech. Eng. Part J-J. Eng. Tribol.
Transient analysis of the textured journal bearing operating with the piezoviscous and shear-thinning fluids
J. Tribol.-Trans. Asme
Comparative analysis of textured and grooved hydrodynamic journal bearing
Proc. Inst. Mech. Eng. Part J-J. Eng. Tribol.
Cited by (9)
Vibration and cavitation in high-speed gears caused by faults
2023, International Journal of Mechanical SciencesA framework for uncertainty quantification of mixed lubrication of conformal contacts in multilevel systems
2023, Advances in Engineering SoftwareCitation Excerpt :Moreover, the govern equation for lubrication calculation is based on two-dimension Reynolds equation rather than N-S equation. It is because film thickness is small and the variation of pressure in film direction can be ignored, which is widely accepted and applied in HJB lubrication calculation [2,39-41]. Reynolds equation has significant advantages: simple form, good convergence and short convergence time.
Numerical prediction of vibration-induced cavitation erosion in high-speed gears using erosion risk indicators
2023, Tribology InternationalCitation Excerpt :Ransegnola et al. [23] employed the HYGESim (hydraulic gear machines simulator), a comprehensive simulation tool for hydraulic pump proposed by Vacca and Guidetti [24], to investigate the pump hydraulic characteristics considering the interaction between the micro motion of gears and the cavitation in the lateral gap and journal bearing. Moreover, Zhu et al. [25] considered the influences of the shaft misalignment and roughness and bearing cavitation in an external gear pump. Mithun et al. [26] discussed the effect of non-condensable gas on the vapor cavity.
Numerical investigation of vibration-induced cavitation for gears considering thermal effect
2022, International Journal of Mechanical SciencesCitation Excerpt :And Wang et al. [34] paid attention to the fluctuating pressure in engine water coolant impacted by the piston lateral slapping force, which is one of the main factors causing cavitation. Ransegnola et al. [35] and Zhu et al. [36] both concerned on the lubricating oil film of the journal bearing mounted on an external gear pump, considering the interaction between cavitation and gear shaft oscillation. Wang et al. [37] simulated the cavitating flow around an axisymmetric slender body vibrating with different amplitudes and frequencies, and found that the cavity length is changed by the body vibration.
CFD-vibration coupled model for predicting cavitation in gear transmissions
2022, International Journal of Mechanical SciencesCitation Excerpt :Different from that, Ramos et al. [18] determined the cavitation features in a journal bearing by solving Reynolds equation combined with a cavitation condition obtained from the Jakobson–Floberg–Olsson cavitation theory, and analysed their effects on the rotor dynamic behaviour. Similarly, Zhu et al. [19] simulated the cavitation in a journal bearing installed in a gear pump by applying the abovementioned model; in addition, they included the unbalanced radial force gears affected by the high pressure fluid. Brunetière [20] calculated the gas mass fraction in oil-lubricated spiral groove thrust bearings.
Study on the Lubrication and Anti-eccentric Load Characteristics of the Aero Gear Pump Bearing
2023, Jixie Gongcheng Xuebao/Journal of Mechanical Engineering