Influence of Cavitation on Unsteady Vortical Flows in a Side Channel Pump

Previous investigation on side channel pump mainly concentrates on parameter optimization and internal unsteady vortical flows.However,cavitation is prone to occur in a side channel pump,which is a challenging issue in promoting performance.In the present study,the cavitating flow is investigated numerically by the turbulence model of SAS combined with the Zwart cavitation model.The vapors inside the side channel pump firstly occur in the impeller passage near the inlet and then spread gradually to the downstream passages with the decrease of NPSHa.Moreover,a strong adverse pressure gradient is presented at the end of the cavity closure region,which leads to cavity shedding from the wall.The small scaled vortices in each passage reduce significantly and gather into larger vortices due to the cavitation.Comparing the three terms of vorticity transport equation with the vapor volume fraction and vorticity distributions,it is found that the stretching term is dominant and responsible for the vorticity production and evolution in cavitating flows.In addition,the magnitudes of the stretching term decrease once the cavitation occurs,while the values of dilatation are high in the cavity region and increase with the decreasing NPSHa.Even though the magnitude of the baroclinic torque term is smaller than vortex stretching and dilatation terms,it is important for the vorticity production along the cavity surface and near the cavity closure region.The pressure fluctuations in the impeller and side channel tend to be stronger due to the cavitation.The primary frequency of monitor points in the impeller is 24.94 Hz and in the side channel is 598.05 Hz.They are quite corresponding to the shaft frequency of 25 Hz(fshaft=1/n=25 Hz)and the blade frequency of 600 Hz(fblade=Z/n=600 Hz)respectively.This study complements the investigation on cavitation in the side channel pump,which could provide the theoretical foundation for further optimization of performance.

Investigation on the Flow Behavior of Side Channel Pumps Based on Vortex Identification

The momentum flow exchange between the impeller and side channel produces highly turbulent flows in side channel pumps.The turbulent flows feature complex patterns of vortex structures that are partly responsible for the dissipation of energy losses and unsteady pressure pulsations.The concept of turbulent flows in side channel pumps requires a reliable vortex identification criterion to capture and predict the effects of the vortex structures on the performance.For this reason,the current study presents the application of the new Ω-criterion to a side channel pump model in comparison with other traditional methods such as Qand λ2 criteria.The 3D flow fields of the pump were obtained through unsteady Reynolds-averaged Navier-Stokes(RANS)simulations.Comparative studies showed that the Ω-criterion identifies the vortex of different intensities with a standard threshold,Ω=0.52.The Q and λ2 criteria required different thresholds to capture vortex of different intensities thus leads to subjective errors.Comparing theΩ-criterion intensity on different planes with the entropy losses and pressure pulsation,the longitudinal vortex plays an important role in the momentum exchange development which increases the head performance of the pump.However,the rate of exchange is impeded by the axial and radial vortices restricted in the impeller.Therefore,the impeller generates the highest entropy loss and pressure pulsation intensities which lower the output efficiency.Finally,the findings provide a fundamental background to the morphology of the vortex structures in the turbulent flows which can be dependent upon for efficiency improvement of side channel pumps.

Numerical investigation on self-priming process of self-priming pump

In order to investigate the self-priming process of the self-priming pump,an unsteady simulation was conducted where the Navier-Stokes equations were used with the Lagrangian-Eularian mo-del.In course of this investigation,the volume fractions,pressure distribution and self-priming time were carried out.By analyzing the volume,velocity and pressure distribution of the gas-liquid two-phase flow at different time,the two-phase content via the variation law of the two-phase flow in the pump was carried out.By monitoring and analyzing the gas-liquid flow at the outlet of the pump,the self-priming time and crucial periods were given.Two phenomena were mainly characterized by the self-priming process such as the gas-liquid mixing and separation,which occur in the early stage of self-priming process.During that period the gas-liquid mixing clouds appear on the outer edge of the impeller,and the instantaneous void fraction at the inlet and outlet of the impeller decreases obviously.It was also established from the transient study that the gas has a major influence on the hydraulic performance of the pump at the early stage of operation.To increase the usage of self-priming pump and to also understand the energy conversion of the pump,it is very essential to investigate and establish the basic working principle of the self-priming pump.

Evaluation of vortex evolution and energy loss within the impeller of a side channel pump

Side channel pumps can provide a huge pressure boost at very low specific speeds,making them useful in various industrial operations.Due to its very complex flow pattern,the high hydraulic head is often accompanied by lower efficiency and higher flow losses.In addition,the shape of the impeller has a direct influence on the flow pattern of the pump as well as the energy conversion that takes place,and this has a substantial bearing on the overall performance of the pump.Thus,to gain a deeper comprehension of the flow behavior and deep-seated reasons for performance optimization in side channel pumps with different geometry parameters.Extensive research has been conducted on the vortex formations and entropy production that occur inside the flow channels of the impeller.Three alternative impeller configurations were systematically created for in-depth research,each including a different suction angle for the blades.According to the data,the head of the side channel pump rises together with an increase in the suction angle,and this rule is exhibited in the whole working condition,and the most effective blade suction angle isθ=30°,which is the greatest of the available options.The vortex area and intensity have an obvious decrease when the suction angle increases to 30°,which is the main reason for the performance optimization.This paper firstly introduces the wall friction dissipation into the research on the side channel pump.Compared with turbulence dissipation and direct dissipation,the wall friction dissipation is far less than turbulence dissipation but far higher than direct dissipation that should not be neglected,although it also increases with the suction angle elevation.As the primary dissipation,the tendency of turbulence dissipation is upward with the performance increase,which is opposite to the common vane pump.The reason for this phenomenon is probably due to the deviation of the primary and secondary flow pattern in the side channel pump.As a result,this will assist to increase the performance and operational dependability of side channel pumps,which will ultimately lead to an expansion of the applications for these pumps.

Influence of pump noise on the health of fish in a large pumping station

The axial flow pump,characteristic of a large flow,is widely used in pumping stations of hydraulic engineering.However,the internal noise of the axial-flow pump of a high sound pressure level is notable,with a great influence on the fishing livelihood.At present,the studies of the impact of the noise on fish are mainly focused on the explosion,the offshore wind power plant,the ship and other fields,with little attention on the noise generated by the pumping station.This paper applies the combination of the computational fluid dynamics and the Actran to study the sound pressure level distribution in the high-noise area inside the axial-flow pump and the noise distribution in the downstream areas of the pumping station.Extensive comparisons are made of the hearing threshold and the hearing damage threshold of fish,and it is revealed that the noise inside the axial-flow pump exceeds the hearing damage threshold of fish,which could lead to the hearing damage of over-pumped fish.Further,the noises emitted from the pumping station to the downstream are beyond the fish hearing threshold and will also have a significant impact on the fish around the pumping station.This study can provide a reference for studying the impact of the noise generated by various large-scale water transfer projects on fish.

A decomposition method of vortex identification and its application in side channel pumps

This research utilizes theΩvortex identification method to address the turbulent flows in a single-stage side channel pump,to comprehensively characterize the three types of dynamic vortex structures classified based on directions.Premised on the Galilean invariance,the work employs coordinate rotation and transformation.Thus,the indistinguishable 3-D vortex can be simplified to 2-D vortex on typical research planes.When juxtaposing the overall performance,it was revealed that a diversity of areas with high values yielded enhanced reflection of the vortex intensity,as measured by velocity distribution.The axial vortex structure with high intensity exists at the outer radius under all conditions largely.While the longitudinal vortex usually shows high intensity between the middle and outer radius.Simultaneously,the radial vortex is more likely to be at the inner radius near the suction face.Finally,this paper introduces a specific valueξ,which represents the ratio of decomposition to the total of the manifestation of the fluid rotational pattern.From the fluctuation and mean value,it can be realized that the development of the specific vortex in three directions at different positions.For example,the specific valueξ2 refers to the typical longitudinal vortex as dynamic vortex are almost from 20%to 50%,which illustrates that the longitudinal vortex only occupies a minor percentage in the total vortex.This phenomenon is one of the main reasons for the low efficiency.The present work could provide some suggestions and references for in-depth studies in fluid engineering with intense swirling flows.