Mixed transportation technology of oil and gas is an efficient transportation method of offshore oil fields, in which oil and gas multiphase pump is the key equipment. In this paper, aimed at a single compression stage unit of a helico-axial multiphase pump prototype, a numerical simulation of internal flow field is carried out. It is assumed that the flow is steady and the two-phase flow pattern is bubble flow. Water is the main phase and incompressible air is the second phase. The change of external characteristics is compared in different inlet gas volume fraction (GVF) condition; the internal flow field characteristics such as velocity fields, pressure fields, and two-phase distributions are discussed as well. The result shows that the differential pressure and the hydraulic efficiency decrease with the increase of GVF, and there are some significant changes in internal flow fields. Further, under the condition of 10% inlet GVF, the changes of external characteristics and internal flow field of the pump when the air bubble diameter varies are compared. The result shows that the differential pressure and the hydraulic efficiency decrease with the increase of bubble diameter.
Unsteady flow phenomena like rotating stall frequently occur in centrifugal pumps under off-design conditions. Rotating stall could lead to flow instabilities and pressure pulsation, which affect the normal operation of pumps. The mechanism of rotating stall has not been sufficiently understood in previous researches. In this study, the impact of rotating stall in the impeller on centrifugal pump stability and pressure pulsation is numerically investigated. This paper aims to detect the unsteady flow characteristics inside the centrifugal pump by computational fluid dynamics technology, to analyze pressure pulsations caused by rotating stall and to explore the propagation mechanism of rotating stall. Unsteady numerical simulations are performed by ANSYS 16.0 to model the unsteady flow within the entire flow passage of a centrifugal pump under 0.4QBEP and 0.6QBEP working conditions. Through flow characteristics research, the generation and propagation of rotating stall are discovered. Flow separation appears near the leading edge of the pressure side and transforms into vortices, which move along the passage. Meanwhile, the stall cells rotate circumferentially in the impeller. Additionally, frequencies and amplitudes of pressure pulsations related to rotating stall are investigated by spectrum analysis. The results detect a possible characteristic frequency of rotating stall and show that the interaction between stall cells and the volute tongue could have an influence on rotor-stator interaction (RSI).
Purpose – The purpose of this paper is to study the pressure fluctuation characteristics in the sidewall gaps
of a centrifugal dredging pump in detail and discover the excitation sources.
Design/methodology/approach – An unsteady numerical simulation with shear–stress transport–
scale-adaptive simulation (SAS-SST) model was conducted for a centrifugal pump considering the sidewall
gaps. The numerical codes were validated by a model test carried out in China Water Resources Beifang
Investigation, Design and Research Co., Ltd. Fast Fourier transform was used to obtain the frequency
components of the pressure fluctuation.
Findings – Pressure fluctuation characteristics inside the pump were analyzed for a condition near the
design point. In the sidewall gaps, the circumferential, radial and axial distribution of the pressure fluctuation
amplitude follow different laws. The non-axisymmetrical distribution of pressure fluctuation in the sidewall
gaps shows that the unsteady flow in the volute casing which has a non-axisymmetrical geometry imposes an
evident effect on the flow field in the sidewall gaps and the interaction between the main flow and the
clearance flow cannot be neglected. There are several frequency components appearing as the dominant
frequencies at different locations in the sidewall gaps, but the relatively stronger pressure fluctuations are all
dominated by the rotating frequency. It indicates that the rotating impeller, which originally makes the
shrouds rotate, is the primarily excitation source of the pressure fluctuations in the sidewall gaps.
Originality/value – The pressure fluctuation characteristics in the sidewall gaps of centrifugal pumps
were first comprehensively analyzed. Unsteady flows in the sidewall gaps should be considered during the
design and operation of centrifugal pumps.
Clearance flows in the sidewall gaps of centrifugal pumps are unsteady as well as main flows in the volute casing and impeller, which may cause vibration and noise, and the corresponding pressure fluctuations are related to the axial clearance size. In this paper, unsteady numerical simulations were conducted to predict the unsteady flows within the entire flow passage of a centrifugal pump operating in the design condition. Pressure fluctuation characteristics in the volute casing, impeller, and sidewall gaps were investigated with three axial clearance sizes. Results show that an axial clearance variation affects the pressure fluctuation characteristics in each flow domain by different degree. The greatest pressure fluctuation occurs at the blade pressure surface and is almost not influenced by the axial clearance variation which has a certainly effect on the pressure fluctuation characteristics around the tongue. The maximum pressure fluctuation amplitude in the sidewall gaps is larger than that in the volute casing, and different spectrum characteristics show up in the three models due to the interaction between the clearance flow and the main flow as well as the rotor-stator interaction. Therefore, clearance flow should be taken into consideration in the hydraulic design of centrifugal pumps.
The influence of prewhirl regulation by inlet guide vanes (IGVs) on a centrifugal pump performance is investigated experimentally and numerically. The experimental results show that IGVs can obviously change the head and increase the efficiency of the tested centrifugal pump over a wide range of flow rates. Although the cavitation performance is degraded, the variation of the cavitation critical point is less than 0.5 m. Movement of the computed three-dimensional streamlines in suction pipe and impeller are analyzed in order to reveal the mechanism how the IGVs realize the prewhirl regulation. The calculated results show that the influence of IGVs on the cavitation performance of centrifugal pump is limited by a maximum total pressure drop of 1777 Pa, about 7.6% of the total pressure at the suction pipe inlet for a prewhirl angle of 24°.
– The purpose of this paper is to experimentally and numerically investigate the interference characteristics between two ski-jump jets on the flip bucket in a large dam spillway when two floodgates are running.
– The volume of fluid (VOF) method together with the Realizable k-ε turbulence model were used to predict the flow in two ski-jump jets and the free surface motion in a large dam spillway. The movements of the two gates were simulated using a dynamic mesh controlled by a User Defined Function (UDF). The simulations were run using the prototype dam as the field test to minimize errors due to scale effects. The simulation results are compared with field test observations.
– The transient flow calculations, accurately predict the two gate discharges compared to field data with the predicted ski-jump jet interference flow pattern similar to the observed shapes. The transient simulations indicate that the main reason for the deflected nappe is the larger opening difference between the two gates as the buttress side gate closes. When both gates are running, the two ski-jump jets interfere in the flip bucket and raise the jet nappe to near the buttress to form a secondary flow on this jet nappe surface. As the gate continues to close, the nappe surface continues to rise and the surface secondary flow become stronger, which deflects the nappe over the side buttress.
– A dynamic mesh is used to simulate the transient flow behavior of two prototype running gates. The transient flow simulation clarifies the hydraulics mechanism for how the two ski-jump jets interfere and deflect the nappe.
Cavitation is one of the key issues affecting the safe and stable operation of centrifugal pumps. This research conducted numerical simulations of the 3-D turbulent flow in the whole flow passage of a centrifugal pump using RANS method. The calculation results of cavitation characteristics agreed well with the experimental results, which were based on SST k-ω turbulence model and Zwart-Gerber-Belamri cavitation model. This paper analysed the cavitation development process and the corresponding pump performance for three typical conditions, namely large discharge condition, design discharge condition and small discharge condition, by changing the available Net Positive Suction Head (NPSHa). For large discharge condition, the incipient NPSHa was large, while for design discharge condition and small discharge condition, the incipient NPSHa values were almost the same and both small. As the flow rate decreased, the critical NPSHa decreased as well, and the cavitation positons gradually shift from the pressure surfaces of some blades to the suction surfaces. At the same time, the tongue has greater effect with larger flow rate and the cavitation becomes less unsteady with the decrease of flow rate. With similar vapour volume, cavitation on the blade pressure side more easily leads to the drop of pump performance. Therefore, more attention should be paid to the cavitation characteristics of centrifugal pumps in large flow conditions in hydraulic design stage.
Among the breakthrough of Poseidon project, the multiphase pump is, certainly, a significant event in the production technology development. The experience acquired leads to a better understanding of multiphase pump performances. Simulation of pump behaviour, bench tests performed at IFP-Solaize (P 300) and field endurance campaign (TOTAL, SIT, Tunisia) are presented. The prediction of two-phase pump performances is the central element in the seek of an optimal design able to comply with real field operational conditions. Based on a physical representation of the kinetic energy transform in the specific two-phase flow conditions related to acceleration field through impeller, e.g. void fraction variation, phase slip velocity, separation effect, an analytical model is proposed and compared with experimental results.
The analytical approach enables the impeller design, considering the parameters sensitivity, and therefore the trends of optimization. However, numerical calculations are evoked and their complementarity pointed out. Experimental bench tests and long term endurance campaign performed on field, achieve the two-phase pumping program.
Recent extensive economic studies emphasize the role played by the multiphase pumping in improving the production when wells are Ia king energy. As far as the North Sea is concerned the main reserves are located at a distance of 50 kms or less from existing facilities, while 80% of discoveries are within 35 kms distance of them.
Created in 1984 by TOTAL, IFP and STATOIL, the POSEIDON project's scope was to review all the multiphase transportation problems and to build a subsea station. Obviously the major element of such a station was the multiphase pump.
At that time no pump capable of handling multiphase effluents was available, hence a dominant effort was agreed upon by the associates to develop an emerging technology reaching an ambitious goal. Based on the studies about what could be the future boosting system requirements, it appeared that a pressure rise between 20 to 50 bars comply with the vicinity of existing facilities, with a flow rates of 40.000 b/d. Situated in well head flow conditions, when no separation has occurred, the pump must cope with the actual production covering the operational conditions.
The present paper analyzed the inner flow characteristic of a reversible pump-turbine at pump mode with the optimal guide vane opening. An unusual asymmetrical feature of both pressure fluctuation and flow pattern inside the rotating impeller was detected under a pump off-design condition, in which the flow rate is smaller than that of hump district. The steady and unsteady simulations were performed in ANSYS 16.0 with the SAS SST-CC turbulence model. The simulation results of pressure fluctuations show that there exists a noteworthy difference of pressure amplitudes in each rotating flow passage, which is not obvious under other conditions. Flow pattern analysis indicates that the impeller flow fields are asymmetrical in different passages under this pump off-design condition, with significant flow separation and vortexes. When exploring the possible causes for this particular flow pattern, it is revealed that the specific elbow structure has an impact on the flow distribution in the draft tube. Flow separation and reverse flow are discovered in the conical and elbow part of the draft tube, which leads to the uneven flow pattern at the impeller inlet. It is demonstrated that there is a close relationship between unsteady flow structures and asymmetrical pressure fluctuation characteristic.
To solve the problem of low accuracy of traditional fatigue crack growth (FCG) prediction methods
The GMSVR model was proposed by combining the grey modeling (GM) and the support vector regression (SVR). Meanwhile, the GMSVR model parameter optimal selection method based on the artificial bee colony (ABC) algorithm was presented. The FCG prediction of 7075 aluminum alloy under different conditions were taken as the study objects, and the performance of the genetic algorithm (GA), the particle swarm optimization algorithm (PSO), the n-fold cross validation(CV) and the ABC algorithm were compared and analyzed.
The results show that the speed of the ABC algorithm is the fastest and the accuracy of the ABC algorithm is the highest too. The prediction performances of the GM (1, 1) model, the SVR model and the GMSVR model were compared, the results show that the GMSVR model has the best prediction ability, it can improve the FCG predic-tion accuracy of 7075 aluminum alloy greatly.
A new prediction model is proposed for fatigue crack growth combined the non-equidistant grey model and the support vector regression model. Aiming at the problem of the model parameters are difficult to select, the GMSVR model parameter optimization method based on the artificial bee colony (ABC) algorithm was presented. the results show that the GMSVR model has better prediction ability, which increase the FCG prediction accuracy of 7075 aluminum alloy greatly.