rotordynamic analysis of a centrifugal pump for automotive applications

Abstract A proper design of a high speed rotating machinery cannot be performed without a deep understanding of the rotor-dynamic aspects involved. The main purpose of the present work is to show how different methodologies can be adopted and integrated, in both preliminary and detailed design phases. The study focused on the dynamic analysis of a centrifugal pump for automotive applications, called purge pump, whose role is to take the air and gasoline vapor mix from the canister to the intake manifold of combustion chambers, in order to reduce emissions. It is quite small and rotates at a constant relatively high speed. The dynamic models were developed using commercial software widely used in companies and in the academic environment. First, an analytical model was devised with all the components assumed as rigid, except the supports. Then a 1-D Finite Element model of the shaft was created with lumped masses and finally a full flexible multibody model for transient analysis, which requires much more computational time with respect to all the other approaches but provides more information, was developed,. In addition to unbalance, localized defects in the pump ball bearings as source of vibration for the pump were investigated. In particular, a detailed 3-D model of faulty ball bearing was set up using a rigid multibody commercial code in order to simulate a localized defect and to evaluate the dynamic load produced. The presented set of methodologies can be a useful tool to understand the critical aspects of the design, as well as to predict the dynamic response and to suggest suitable modifications for a better rotor-dynamic behavior of the whole system reducing vibrations and consequently acoustic noise and improving structural reliability

Development of a One-Dimensional Model for the Prediction of Leakage Flows in Rotating Cavities Under Non-Uniform Tangential Pressure Distribution

Regenerative pumps are characterized by a low specific speed that place them between rotary positive displacement pumps and purely radial centrifugal pumps. They are interesting for many industrial applications since, for a given flow rate and a specified head, they allow for a reduced size and can operate at a lower rotational speed with respect to purely radial pumps. The complexity of the flow within regenerative machines makes the theoretical performance estimation a challenging task. The prediction of the leakage flow rate between the rotating and the static disks has the greatest impact on the prediction of global performance. All the classical approaches to the disk clearance problem assume that there is no relevant circumferential pressure gradient. In the present case, the flow develops along the tangential direction and the pressure gradient is intrinsically non-zero. The aim of the present work is to develop a reliable approach for the prediction of leakage flows in regenerative pumps. A preliminary numerical simulation on a virtual model of a regenerative pump where the disk clearance is part of the control volume has been performed for three different clearance aspect ratios. The outcome of that campaign allowed the authors to determine the behavior of the flow in the cavity and choose correctly the baseline hypotheses for a mathematical-physical method for the prediction of leakage flows. The method assumes that the flow inside of the disk clearance is two-dimensional and can be decomposed into several stream-tubes. Energy balance is performed for each tube, thus generating a system that can be solved numerically. The new methodology was tuned using data obtained from the numerical simulation. After that, the methodology was integrated into an existing one-dimensional code called DART (developed at the University of Florence in cooperation with Pierburg Pump Technology Italy S.p.A.) and the new algorithm was verified using available numerical and experimental data. It is here demonstrated that an appropriate calibration of the leakage flow model allows for an improved reliability of the one-dimensional code

Dynamic and kinematic evaluation of automotive variable displacements vane pumps for reliability characterization

This study deals with the design of variable displacement oil pumps, with particular focus on wear of the inner components. A multibody model has been developed in order to achieve detailed knowledge on the dynamic loads which the main components are subjected to and to carry out a comparative analysis between different pump designs. A qualitative correlation, between the resulting wear following endurance tests and simulation results, has also been found. Design guidelines leading up to a good pump reliability have been obtained as a result of this activity

Modelling of a Variable Displacement Lubricating Pump with Air Dissolution Dynamics

The simulation of lubricating pumps for internal combustion engines has always represented a challenge due to the high aeration level of the working fluid. In fact, the delivery pressure ripple is highly influenced by the effective fluid bulk modulus, which is significantly reduced by the presence of separated air. This paper presents a detailed lumped parameter model of a variable displacement vane pump with a two-level pressure setting, in which the fluid model takes into account the dynamics of release and dissolution of the air in the oil. The pump was modelled in the LMS Imagine.Lab Amesim® environment through customized libraries for the evaluation of the main geometric features. The model was validated experimentally in terms of pressure oscillations in conditions of low and high aeration. The fraction of separated air in the reservoir of the test rig was measured by means of an X-ray technique. The pump was tested in two different configurations of the displacement control: direct acting for the low-pressure level, pilot operated for the high setting. It was found that the former configuration is more sensitive to the presence of separated air, since the variation of the pressure peaks in the variable volume chambers alters the equilibrium of the stator ring. Overall, the model has been proved to be reliable not only for the evaluation of the mean pressure level imposed by the displacement control, but also in the assessment of the pressure amplitude and in most cases even in the reproduction of the pressure waveform

One-Dimensional Prediction and Three-Dimensional CFD Simulation of the Fluid Dynamics of Regenerative Pumps

Regenerative pumps, also referred to as “peripheral” or “side channel” pumps, are characterized by a specific speed that contextualize them between rotary positive displacement and purely radial centrifugal pumps. Although regenerative pumps are not widely distributed, they are interesting for many industrial applications. In fact, for a given flow rate they operate at lower rotational speed with respect to purely radial pumps. Furthermore, they are less affected by mechanical problems with respect to positive displacement pumps. The energy transfer mechanism is the same of centrifugal pumps, but the presence of the side channel imposes to the fluid to pass several times through the impeller, thus obtaining higher pressure rise (as for multi-stage machines) with respect to classical purely radial pumps. Unfortunately, the complexity of the flow field, the large amount of wetted surface and a disadvantageous inflow/outflow configuration contribute to limit the maximum value of hydraulic efficiency, which is also very sensitive to the design choices. Moreover, the intrinsic complexity of the helical flow path makes the theoretical performance estimation a challenging task. It is worth underlining that an accurate performance prediction using one-dimensional models would allow to accelerate greatly the design process, with a non-negligible reduction of demanding three-dimensional Computational Fluid Dynamics (CFD) campaigns. The aim of the present work is to deeply investigate the fluid dynamics of regenerative pumps and to understand how accurately the fundamental physical phenomena can be reproduced by one-dimensional theory. To comply with these aims, a systematic post-processing of the results of several steady and unsteady three-dimensional CFD simulations is exploited for the validation of the in-house one-dimensional tool DART (Design and Analysis tool for Regenerative Turbomachinery), developed at the University of Florence. The theory underlying DART is detailed, and the assumptions of the model are verified by means of comparison with the numerical results underlining the key aspects to be considered for a reliable prediction of the pump performance

Mechanical combustion-engine-driven fluid pump (Magnetorheological Electrodynamic Permanent Magnet Clutch) [US9976606 - US2015260240A1]

A mechanical combustion-engine-driven fluid pump includes an input shaft driven by a combustion engine, a pumping unit comprising a pump rotor, and a clutch arranged between the input shaft and the pump rotor. The clutch comprises an input clutch body, an output clutch body, an electroconductive element, a permanent magnet element, and an actuator. The clutch transfers a rotation of the input clutch body to the output clutch body in an engaged clutch state. The closed clutch liquid gap is formed between the input clutch body and the output clutch body, and is filled with a magneto-rheological clutch liquid. The electroconductive element co-rotates with the output clutch body. The permanent magnet element co-rotates with the input clutch body and is shiftable between an engaged position and a disengaged position. The actuator moves the permanent magnet element between the engaged position and the disengaged position