Search

The multiphase rotodynamic pump is crucial for the multiphase blending transportation process. However, desigining such pump with high hydraulic performance and good blending transportation ability is quite challenging because of its unique structure. This study constructed a multi-objective optimization design system, which combines the 3D inverse design theory, response surface methodology, genetic algorithm, computational fluid dynamics simulation, and multi-objective optimization strategy, to improve the multiphase pump performance. Five optimization variables, namely the impeller loading parameters ( m1,S, m1,H, kS, kH) and the high-pressure edge angle ( θ), were selected in this study. Furthermore, two optimization objectives were considered at inlet gas void fraction ( IGVF) = 10%, namely the pump efficiency and the gas uniformity at the impeller outlet. The optimization results demonstrated that the pump efficiency and blending transportation ability would improve if the impeller blades had for-loaded loading distribution and the negative high-pressure edge angle. After optimization, the pump efficiency and the gas uniformity for the optimized impeller Opt1 improved by 2.6% and 18.2% at IGVF = 10%, respectively. Moreover, the internal flow pattern in the impeller was improved significantly, resulting in the maximum amplitude of pressure fluctuation in impeller Opt1 being 0.42 times that in the original test impeller.

Hydropower is one environmentally friendly option for meeting these energy demands. Because such technologies do not require a weir or a dam, they may be used with minimal environmental effect. The drag-based Savonius turbine is characterized by working at low-flow speeds which fits well the natural water streams. In spite of its simple and robust design, the Savonius turbine suffers from low efficiency and high static torque fluctuations. In view of this, CFD-based optimization is applied to a Savonius-type hydrokinetic turbine inspired by a couple of swimming Koi fish. The two main design parameters; overlap ratio and gap ratio are used in this paper to define the gap between the blades. The maximum power coefficient can be obtained by employing an evolution strategy optimization technique over the constructed metamodel. The results revealed that the optimal design for the bio-inspired Savonius hydrokinetic turbine corresponds to overlap and gap ratios of 0.2085 and 0.0057, respectively. The optimal configuration generates a maximum power coefficient of 0.2521, which is 17.6% higher than that for a conventional shape at the same tip speed ratio. The new bio-inspired design performs better than the conventional Savonius hydrokinetic turbine for the considered operating range.

A centrifugal impeller with splitters was designed by three-dimensional (3D) inverse design method, and its efficiency, velocity non-uniformity at impeller exit and maximum equivalent stress of blades were optimized by providing the suitable blade stacking angle, work ratio and circumferential location of the splitter. First, 80 samples were generated by optimal Latin hypercube technique and the corresponding impellers were designed by 3D inverse design. Using computational fluid dynamics (CFD) and fluid structure interaction (FSI), the optimization objectives were obtained. Then, the group method of data handling (GMDH) artificial neural networks was established to link the design parameters and objectives by the specific formulas. The reference-point-based non-dominated sorting genetic algorithm (NSGA- III) was applied to search the Pareto front. Finally, the preferred impeller was selected by adopting entropy weight and the method of technique for order preference by similarity to an ideal solution (TOPSIS). The results showed that the splitter of the preferred impeller had a circumferential location of 0.58, blade stacking angle of 28° and work ratio of 0.48. The nonuniformity at impeller exit and maximum equivalent stress of blades of preferred impeller obtained by NSGA-III were decreased, while the efficiency was improved.

Due to the effect of unit stages, the gas-liquid flow and the interphase forces in the multistage multiphase pump are more disordered, which will affect the energy conversion efficiency. However, the characteristics of phase interaction and gas holdup in such a pump are not clear. In this study, based on a modified Euler two-fluid model, simulations of a multiphase rotodynamic pump with two stages were carried out with medium combinations of air-water and air-crude. The characteristics of phase interaction and gas holdup were analyzed at different inlet gas void fractions (IGVFs), and inlet bubble diameters. The results show that the overall changing trend of interphase forces is the same between the first and second stages at different IGVFs, but the magnitudes of interphase forces in the second stage are slightly smaller, especially for the medium combination of air-water. Moreover, the drag is more sensitive to the IGVF, while the lift and added mass force are more sensitive to the medium viscosity. As the increase of the inlet bubble diameter, the difference of the gas holdup effect in the pump increases gradually at IGVF = 9.0%, and the maximum almost occurs in the first stage guide vane (S1). When the bubble diameter increases to 0.7 mm, the degree of gas accumulation and gas-liquid velocity difference increase significantly, resulting in a significant increase of the disordered degree of lift and added mass force.

Purpose This study aims to complete the optimization design of a centrifugal impeller with both high aerodynamic efficiency and good structural machinability. Design/methodology/approach First, the design parameters were derived from the blade loading distribution and the meridional geometry in the impeller three-dimensional (3D) inverse design. The blade wrap angle at the middle span surface and the spanwise averaged blade angle at the blade leading edge obtained from inverse design were chosen as the machinability objectives. The aerodynamic efficiency obtained by computational fluid dynamics was selected as the aerodynamic performance objective. Then, using multi-objective optimization with the optimal Latin hypercube method, quadratic response surface methodology and the non-dominated sorting genetic algorithm, the trade-off optimum impellers with small blade wrap angles, large blade angles and high aerodynamic efficiency were obtained. Finally, computational fluid dynamics and computer-aided manufacturing were performed to verify the aerodynamic performance and structural machinability of the optimum impellers. Findings Providing the fore maximum blade loading distribution at both the hub and shroud for the 3D inverse design helped to promote the structural machinability of the designed impeller. A straighter hub coupled with a more curved shroud also facilitated improvement of the impeller’s structural machinability. The preferred impeller was designed by providing both the fore maximum blade loading distribution at a relatively straight hub and a curved shroud for 3D inverse design. Originality/value The machining difficulties of the designed high-efficiency impeller can be reduced by reducing blade wrap angle and enlarging blade angle at the beginning of impeller design. It is of practical value in engineering by avoiding the follow-up failure for the machining of the designed impeller.

To understand the pressure fluctuations occurring in S-shaped region of the pump-turbine and their relationships with rotor-stator interaction, rotating stall and vortex rope, the numerical and experimental studies of a reversible pump-turbine were conducted under turbine, runaway, turbine brake, small flow rate and reverse pump operating modes. The experimental results show that pressure fluctuations under turbine mode were most affected by the guide vane opening. This effect was weaker under turbine brake mode and weaker still under reverse pump mode. At a guide vane opening of 19 mm, the maximum fluctuation peak in the vaneless space is 5.7 times, 6.9 times and 2.0 times greater than that in the spiral casing inlet, draft tube cone and draft tube elbow, respectively. Unsteady simulation results for the whole flow passage of the pump-turbine show that asymmetric flow occurred in the runner under turbine, runaway and turbine brake operating modes. Meanwhile, an obvious rotating stall vortex with a frequency of 0.65fn was generated in turbine brake mode, resulting in relatively large pressure fluctuations in the vaneless space. At the small flow rate, flow separation in the vaneless space became very obvious, while that in the runner weakened, resulting in decreased pressure fluctuations in the vaneless space. Under reverse pump mode, pressure fluctuations in the vaneless space were relatively small because of obvious symmetrical flow separation in the runner. Pressure fluctuations in the draft tube were mainly attributed to the combined actions of rotating stall and vortex rope phenomena. What’s more, the fluctuation amplitudes at the rotating stall frequency of 0.65fn and the vortex rope frequencies of 0.30fn and 0.17fn were relatively large.

A pumped hydro storage energy station (PHES) is an effective and reliable station which was quickly develop. To obtain better performances, blade leans have been employed recently on pump-turbine runners. To figure out the effect of the blade leans in turbine mode, numerical simulations were performed on two blade-leaned and no-leaned runners in this work. Because blade leans were on high-pressure edges, the vaneless space was paid chiefly attention. Distinctions due to the blade leans can be found in the spanwise direction. Amplitudes of the component of blade passing frequency in pressure fluctuations show nonuniformity at different vertical locations. While in no-leaned runners, the amplitudes are almost the same. It shows close correlations between the pressure fluctuations and blade leans. In addition, this difference was more prominent in the S-shaped region. The conditions were attributed to the different separations at the inlets of runners. Separations located at the pressure side of the blades and developed vortexes located near the hub, the shroud and at the middle span for runners respectively. The vortexes generated low-pressure areas producing a higher fluctuation in the vaneless space with the same frequency of blade passing when they rotated with the runner.

Purpose The purpose of this study is to suppress secondary flows and improve aerodynamic performance of a centrifugal impeller. Design/methodology/approach A multi-objective optimisation design system was described. The optimization design system was composed of a three-dimensional (3D) inverse design, multi-objective optimisation and computational fluid dynamics (CFD) analysis. First, the control parameter ΔCp for the secondary flows was derived and selected as the optimisation objective. Then, aimed at minimising ΔCp, a 3D inverse design for impellers with different blade loading distributions and blade lean angles was completed and multi-objective optimisation was conducted. Lastly, the improvement in the distribution of secondary flows and aerodynamic performance of the optimal impeller was demonstrated by CFD analysis. Findings The study derived the control parameter ΔCp for the secondary flows. ΔCp can indicate the distribution of secondary flows both near the blade pressure and suction surfaces. As ΔCp decreased, secondary flows decreased. The blade loading distribution with fore maximum blade loading at the shroud and aft maximum blade loading at the hub, coupled with a small negative blade lean angle, could help suppress secondary flows and improve aerodynamic efficiency. Originality/value A direct control method on internal flow field characteristic-secondary flows by optimisation design was proposed for a centrifugal impeller. The impeller optimisation design process saves time by avoiding substantial CFD sample calculations.

To study the pressure pulsations induced by quasi-steady cavitation in a centrifugal pump, the pressure pulsations at the pump inlet and outlet were experimentally investigated with the development of cavitation. Moreover, the internal flow characteristics in the pump during the process were numerically determined. The numerical simulation results agreed well with the results obtained from the experimental test, verifying the accuracy of the numerical simulation. Furthermore, the cavitation-induced pump inlet and outlet pressure pulsations of the centrifugal pump were analyzed by wavelet analysis and fast Fourier transform, and the cavitation incipient point and occurrence of the unstable cavitation point were obtained. The results of both wavelet analysis and fast Fourier transform show that in the quasi-steady cavitation stage of the centrifugal pump at the design flow rate, the pump inlet and outlet pressure pulsations are significantly increased at twice the axial frequency, while the other axial frequency components are weak and the internal flow is stable. With the development of cavitation in the pump, the pump inlet and outlet pressure pulsations at the axial frequency and its multiples afford some obvious broadband pulsations. To investigate the mechanism of quasi-steady cavitation-induced pressure pulsation in the centrifugal pump, the dynamic mode decomposition was used for internal flow field analysis. The results show that different inflow states lead to obvious differences in the internal flow and unsteady flow structures. There are complex pressure pulsation characteristics dominated by different frequencies in the centrifugal pump. Blade passing frequency plays an important role in the entire flow field, and its mechanism has been analyzed. This research will provide experimental and theoretical support for quasi-steady cavitation recognition and help researchers improve the operation stability of the centrifugal pump.

Sediment erosion in guide vane of Francis turbine has been a crucial issue for turbines operating in Himalayas. Large sediment load with higher percentage of Quartz in Himalayan river causes erosion on GV faces, leaf, stem, leading and trailing edges and at clearance gaps (both facing plate and GV edges). This in turn increases profile roughness and clearance gaps height, causing higher friction losses and cross flow across the vanes, which ultimately affects inlet flow dynamics. Research attempts are limited to computational analysis and prediction of erosion losses. The effect of erosion on flow passing vanes is a crucial issue yet to be explored. This work focuses on experimental prediction of effect of erosion in 3 GV cascade system. The cascade geometry was developed with CFD based iterative method, maintaining flow similarity around GV in turbine and cascade. It has been found that the pressure on two sides of vane and at vane outlet increases with erosion for considered extent erosion.

In this study, a time-domain numerical method using dynamic stiffness matrices is proposed to obtain the characteristics of the vortex induced vibration (VIV) of a flexible riser. Due to the large ratio of length to diameter, a marine riser is approximated as a cable model. Based on the finite volume method (FVM), the cable model of the riseris dividedinto a certain number of segments. The dynamic stiffness matrix of each segment reflecting the time varying strain energy and bending stiffness are updated in calculation. The total dynamic stiffness matrix of the riser is then obtained by the superposition characteristics of the finite volume method. In the nonlinear governing equation of riser's vibration, the hydrodynamic forces are calculated by the instantaneous vorticity conserved boundary condition (IVCBC) method and the equation is solved by the step-by-step time integration method to obtain the accelerations, velocities and displacements of the riser. Validation of this numerical approach is carried out by comparing the static balance and the dynamic responses with quantities in classical experimental cases for a riser in uniform flow. The results show that:when the vibration of riser is high order mode vibration, the dynamic stiffness matrix cannot be ignored. The vortex induced vibration of the given flexible riser has a strong coupling effect between the deformation of riser and flow field. In the vibtation of the riser, there exists the multiple-frequency effect, numely, adominant frequency co-exists with some subordinate frequencies, hence the shedding frequencies can no longer be satisfied with the distributions of the Strauhal number. The wake effect onthe vortex shedding has a stronger 3-dimensional effect at the locations of smaller lateral vibrations. The numerical simulations also reveal that the vibration mode increases with the flow velocity.

Advanced measurement technology on boundary layer transition is an effective means to study the flow mechanism and the performance of the cascade. In this research, to investigate the boundary layer transition of transonic VKI-RG turbine cascade, a noncontact measurement technique named temperature-sensitive paint (TSP) that is capable of quantitatively measuring the surface temperature of a model is used. Under the conditions of outlet Mach number (Ma2) = 0.4, 1.03, and 1.2, the transitional location of a cascade is accurately measured by TSP technique. Moreover, a numerical study on the transitional location of a planar cascade was conducted with the conditions of Mach number (Ma) and attack angle (α). The numerical results show that the transitional location moved forward with the increase in Ma2 and α at Ma2 < 1; otherwise, the transitional location moved backward with increasing Ma2 (Ma2 > 1). Lastly, a strong adverse pressure gradient was formed behind the shock wave, which led to the beginning of the transition.

To investigate the unsteady evolution characteristics and mechanism of cavitation at the tongue and its influence on the flow field in a centrifugal pump, numerical calculations were performed to research the occurrence and development of cavitation at the tongue under large flow rate (1.3 Qd) conditions. The numerical calculation results were verified by experiments. The proper orthogonal decomposition (POD) method was used to decompose and reconstruct the flow field at the tongue of the centrifugal pump. The relationship between the typical frequency of pressure pulsation and the mainstream structure of the flow field was established. The POD method could accurately extract the coherent structure caused by cavitation and capture the unstable flow structure produced by vortex shedding. Under different available net positive suction head conditions, the first mode was the mainstream structural mode in the original flow field, with low-frequency and single-frequency components. The second, third, and fourth modes were the main oscillation modes of the original flow field and showed the characteristics of high frequency and multiple frequencies. High-order modes could capture the complex flow field structure caused by the change in the large-scale vortex structure induced by the unsteady pulsation of cavitation.

To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.

Leading-edge tubercles on the humpback whale pectoral fin are known to have aerodynamic benefits, particularly in the post-stall regime. In this research, a horizontal-axis wind turbine blade was modelled with tubercles distributed on its leading edge to mimic the humpback whale pectoral fin. A parametric study of the effect of tubercles on the reference NREL Phase VI wind turbine was conducted via computational fluid dynamics. Three parameters—amplitude, wavelength, and tubercle location along the blade span—were varied. The results showed that tubercles have negative effects on the turbine performance at wind speeds (V∞) ≤ 7 m/s. However, when tubercles are placed over 60% of the blade span, the backflow area can be eliminated at V∞ = 10 m/s. It is found that the vortices in the stable-flow zone over the suction surface can be reduced when tubercles of a relatively small amplitude-wavelength ratio are employed, thereby maintaining turbine performance. Compared with the reference blade, tubercles provided benefits at higher wind speeds. The generated vortices due to the presence of tubercles, leading to both blockage effects and stall delay. The results revealed that the pressure on the suction surface of the tubercled blade decreases, thereby increasing lift and enhancing the turbine performance.

Synchronous condenser mode is an important process for the conversion of pumped storage units. The compressed air is injected into the runner passage to reduce the input power under the condition of pump mode’s starting-up. In this study, a pump turbine model with medium specific speed was utilized for investigating the internal flow characteristic of water-ring. Unsteady state analysis was conducted with the turbulence model of RNG k-ε and multiphase flow model of VOF. The internal flow of the vaneless and the tandem cascade spaces was examined under the water-ring phenomenon. The results show that the air and water form an interface in the vaneless space obviously and a certain thickness of water-ring was formed. Water-ring prevents the air from runner passage into casing, which play a sealing role.

Magnetic fluid seals (MFSs) have been widely used as a gas seal because of its advantages such as low wear, zero leakage, and long service life. However, the MFS is generally unstable due to structural- and material-related challenges in a liquid environment. To improve the pressure resistance and durability of the sealing liquid, we proposed an improved structure, where the annular pole component is designed as a radially magnetized annular permanent magnet. Furthermore, the structural parameters are optimized to maximize the magnetic induction intensity in the sealing gap. An MFS test device was simultaneously designed, according to the optimized results, to test the pressure resistance and durability under static and dynamic conditions. The results show that the pressure resistance and durability of the improved MFS structure is better than those of the traditional structures, specifically for a large gap structure. Furthermore, in a static seal, the sealing performance depends on the magnetic fluid magnetic saturation rather than other physical parameters, while in dynamic sealing, although magnetic saturation is a primary factor, the viscosity of the magnetic fluid also affects the sealing performance. Furthermore, the high-viscosity magnetic fluid had a higher critical pressure, while the low-viscosity magnetic fluid improved the durability of the seal. This result provides a reference for designing a magnetic fluid sealing device in a liquid environment.

In guide vane cascade of Francis turbine, highest acceleration occurs, which generates equivalent amount of force for work done and erosion due to instantaneous change in flow dynamics. Hence in addition to runner vane, suitable selection of guide vane profile has equal importance. Usually, NACA defined hydrofoils are used for guide vanes. Numerous options are available, but selection of best one for optimum energy harness is important. Primarily, guide vane torque and turbine efficiency is prioritized. For the turbines operating in sediment laden water, pressure difference between two sides of guide vane and erosion resistivity are additional factors to be considered. This work was performed in the vicinity of guide vane profile selection for Francis turbines operating in sediment laden water. Computational analysis on turbine flow passage and experimental study with Rotating Disc Apparatus were performed in order to identify suitable profile. Unsymmetrical profiles were found to be better handling erosion maintaining consistency in turbine performance.

Guide vanes in Francis turbine faces frequent erosion due to its operation in sand laden water, which demands focus on design, manufacturing, operation and maintenance of turbines. These vanes are designed on high precision with standard hydrofoils for efficient conversion of pressure to kinetic energy. The erosion on surfaces, upper and lower ends and leading and trailing edges of guide vanes induces cross flow at clearance gaps, tip leakage at trailing edges and high friction on the surfaces, increasing hydraulic losses associated with flow. Review on post erosion hydraulic and mechanical effect on guide vanes and its vicinity are the main objectives of this work. It has been assisted by flow around vanes, field observation of erosion, possible operational problem and method of laboratory estimation of erosion. The vulnerable locations, erosion severity, possible post erosion problems, research gap and possible measures to comprehend them have been focused, which will be useful in further research activities.

The pressure fluctuations and flow pattern in a mixed-flow pump are numerically investigated under design and off-design conditions. The accuracy and reliability are validated by good agreement of numerical results and experimental data of pump energy performance. At design flow rate, the dominant frequencies of pressure fluctuations are impeller rotation frequency or integer multiples of it, which are mainly induced by the rotor–stator interaction. At overload condition, the dominant frequencies of pressure fluctuations are similar as those of design flow rate, but the maximum amplitudes increase to about 2.5 times of those of design flow rate. At partial load condition, the pressure fluctuations and flow pattern are complicated. The low dominant frequencies below the impeller rotation frequency are related to the process of vortex emergency, movement and disappearance.

In order to investigate the mechanism and the characteristics of the noise induced by unstable flow in a centrifugal pump, the internal flow characteristics in the pump were numerically researched, and the acoustic pressure fluctuations at the pump inlet and outlet were experimentally investigated. Obvious corresponding relationships between the flow instabilities, the cavitation and the noise were established. It was found that the rotating stall, the backflow, the hump, the occurrence of unstable flow and the cavitation in such a centrifugal pump were effectively detected through the noise, which could help to provide fundamental information on flow instabilities and guarantee safe and steady operating conditions for the system. The recirculation and prewhirl regions in the pump upstream pipe, which were caused by the backflow and the rotation of the impeller, presented the circumferential movement with a spiral shape, causing apparent broadband fluctuations at low frequency band of the acoustic pressure. The backflow and rotating stall could also result in broadband fluctuations of the pump outlet noise, which was distributed from 100 Hz to 150 Hz. Meanwhile, the broadband fluctuations of the pump outlet acoustic pressure distributed in the low frequency range, which was produced by the occurrence of cavitation, moved to the lower frequency band as the flow rate increased. The enhanced broadband fluctuations of the pump inlet and outlet noise distributed from 1 kHz to 6 kHz were caused by the coupling between the cavitation-induced noise and the system-produced noise. The broadband fluctuations of the pump inlet noise distributed between 6 kHz and 9 kHz were regarded as the typical frequency band of cavitation in the centrifugal pump.