Search Results (17)

Blade wear is the critical problem in the operation of multiphase pump. This paper presents a numerical study of the multiphase flow of multiphase pump. The trajectory of particles in the pump is calculated by the discrete phase model. Then, the simulation results are compared with the model test results of the pump to verify the correctness of the simulation method. The results show that the particles in the impeller domain are mainly near the hub, and the particles in the diffuser domain form a agglomerated area in the middle of the flow channel. The average wear rate of the impeller is more affected by the particle size than that of the diffuser. The maximum wear rate of blade surface increases first and then decreases with the increase of particle size. According to the wear data under different particle sizes, the regression model between particle size and wear rate is fitted to predict the wear of mixed transport pump in actual operation. The research results have important reference value for the prediction of the wear performance of the multiphase pump. Full article

Due to the extremely low Reynolds number, the mixing of substances in laminar flow within microfluidic channels primarily relies on slow intermolecular diffusion, whereas various rapid reaction and detection requirements in lab-on-a-chip applications often necessitate the efficient mixing of fluids within short distances. This paper presents a magnetic pillar-shaped particle fabrication device capable of producing particles with planar shapes, which are then utilized to achieve the rapid mixing of multiple fluids within microchannels. During the particle fabrication process, a degassed PDMS chip provides self-priming capabilities, drawing in a UV-curable adhesive-containing magnetic powder and distributing it into distinct microwell structures. Subsequently, an external magnetic field is applied, and the chip is exposed to UV light, enabling the mass production of particles with specific magnetic properties through photo-curing. Without the need for external pumping, this chip-based device can fabricate hundreds of magnetic particles in less than 10 min. In contrast to most particle fabrication methods, the degassed PDMS approach enables self-priming and precise dispensing, allowing for precise control over particle shape and size. The fabricated dual-layer magnetic particles, featuring fan-shaped blades and disk-like structures, are placed within micromixing channels. By manipulating the magnetic field, the particles are driven into motion, altering the flow patterns to achieve fluid mixing. Under conditions where the Reynolds number in the chip ranges from 0.1 to 0.9, the mixing index for substances in aqueous solutions exceeds 0.9. In addition, experimental analyses of mixing efficiency for fluids with different viscosities, including 25 wt% and 50 wt% glycerol, reveal mixing indices exceeding 0.85, demonstrating the broad applicability of micromixers based on the rapid rotation of magnetic particles. Full article

The application of centrifugal compressors is extensive in industries such as aerospace and energy. The blade is the primary factor affecting the aerodynamic performance of compressors. In this paper, the aerodynamic performance of a centrifugal compressor with leaned and bowed 3D blades is investigated. The spanwise section profiles of the blade in the circumferential direction are deflected at different angles, resulting in four compressors with distinct leaned and bowed 3D blades based on the original model. There is a significant change in isentropic efficiency of the modified models under design conditions. Specifically, models 1, 3, and 4 experienced an increase of 0.97%, 1.04%, and 0.79%, respectively, while model 2 experienced a decrease of 0.70%. The profile of the blade tip and 50% spanwise section are shifted towards the suction surface, resulting in a geometric structure where the blade is concave towards the pressure surface. This structure gradually lifts the flow from the blade root to the blade tip downstream to the outlet area of the flow channel, reducing the load on the trailing edge of the blade and making the flow more closely aligned with the blade. At the same time, the larger radial velocity gradient near the blade tip suppresses the backflow on the shroud side, making the flow at the impeller outlet more stable. The outlet velocity of the impeller is more evenly distributed along the spanwise and circumferential directions, which improves the flow at the inlet of the diffuser and enhances the efficiency of the diffuser. Due to the high spanwise height of the leading edge of the blade, this bowed blade structure has little effect on the spanwise curvature upstream of the blade, resulting in negligible influence on the flow of the upstream channel. Full article

When we tested the water jet propulsion pump, we found that there were significant vibrations in the pump, especially at small flow points that deviated from the design conditions. The water jet propulsion pump is a mixed-flow pump with guide vane, which is commonly employed for water jet propulsion. However, the guide vane mixed-flow pump is susceptible to a phenomenon known as “hump”, which can cause flow disturbances, increased vibration, and noise when the pump operates within the hump region. According to the vibration phenomenon found in our experiment, the mechanism of vibration needs to be revealed. This study focuses on vorticity and turbulence distributions of a mixed flow water jet propulsion pump under the valley and peak operating conditions of the hump region. The research is conducted using experimental and numerical simulation methods. The SST k-ω turbulence model is employed for turbulence calculations. The experiments are conducted on a closed test rig for axial (mixed) flow pumps. A comparison of experimental and numerical simulation results of hydraulic performance curves are conducted to validate the accuracy of the numerical simulation. Cavitation flow structures of the critical cavitation stage under valley conditions and under peak conditions are compared. A comparative analysis is conducted to examine the differences in internal vortex core distribution and turbulence kinetic energy distribution between the valley and peak operating conditions when working within the hump region. The pressure and velocity vectors of the pump impeller blades and the velocity streamline distribution between the impeller and the guide vane blades are compared. To further analyze the flow state in different flow channels under valley and peak conditions, the streamline distribution at Span = 0.5 in the impeller and diffuser basin is extracted. This study provides theoretical foundations and technical support for the design of high-performance, low-vibration water jet propulsion pumps. Full article

In order to study the internal flow characteristics of the electric submersible pump (ESP) when the gas–liquid two-phase flow is conveyed by the variable frequency variable speed operation and the change of the imported gas content, the impeller of the Q10# ESP is taken as the research object, based on the Eulerian-Eulerian non-homogeneous phase. The flow model, the unsteady Reynolds time-averaged N-S equation, and the standard k-ε turbulence model are used for transient simulation calculations of the gas–liquid two-phase flow in the impeller of the ESP. Calculations show that with the rotation of the impeller, the gas phase is unevenly distributed in the flow channel. The gas phase is mainly concentrated on the inlet side of the flow channel near the front cover, and the gas phase exhibits periodic aggregation and diffusion in the flow channel. When the impeller speed increases, the period of periodic accumulation and diffusion of gas in the flow channel is shortened and the gas concentration in the impeller decreases, the overall flow velocity in the flow channel increases, and the pressure difference between the inlet and outlet increases. The pressure difference between the two sides of the blade is proportional to the speed of the impeller, and the fluctuation frequency of the blade surface also increases. As the gas content increases, the maximum concentration of gas phase in the flow channel increases. The area occupied by the high concentration of gas phase in the flow channel expands toward the blade’s working surface, and periodically accumulates, diffuses, and grows. The gas-liquid splitting area shrinks toward the front cover side and the pump. The internal pressure increases slightly, the main flow velocity increases, and the vortex action range increases. Full article

The research object was a Francis turbine, and the working conditions at 100%, 75%, 50%, 25%, and 1% opening were determined by the opening size of the guide vane. Large-Eddy Simulation (LES) was adopted as a turbulence model method to conduct three-dimensional unsteady turbulent numerical simulation of the entire flow channel of a Francis turbine, and the flow situation of various parts of the turbine under different working conditions was obtained. The flow characteristics of each component under different working conditions were analyzed, and the hydraulic performance of each part was evaluated. The factors that affected the stability of hydraulic turbines were identified, and their formation mechanisms and evolution laws were explored. The results show that the guide vane placement angle was reasonable in the guide vane area, and the hydraulic performance was fine. The impact on the stability of the hydraulic turbine was small. Further research showed that the hydraulic performance was poor in the runner area, and there were flow separation and detachment phenomena in the flow field. This created a channel vortex in the runner blade channel. The channel vortex promoted the lateral flow of water and had a significant impact on the stability of the hydraulic turbine. The diffusion section of the draft tube can dissipate most of the kinetic energy of the water flow in the draft tube area, and it had a good energy dissipation effect. However, the was a large pressure difference between the upper and lower regions of the diffusion section, and it generated a backflow phenomenon. It created vortex structures in the draft tube, and the stability of the hydraulic turbine was greatly affected. Full article

Double-regulated Kaplan turbines with adjustable guide vanes and runner blades offer a high degree of flexibility and good efficiency for a wide range of operating points. However, this also leads to a complex geometry and flow guidance with, for example, vortices of different sizes and strengths. The flow in a draft tube is especially challenging to simulate mainly due to flow phenomena, like swirl, separation and strong adverse pressure gradients, and a strong dependency on the upstream flow conditions. Standard simulation approaches with RANS turbulence models, a coarse mesh and large time step size often fail to correctly predict performance and can even lead to wrong tendencies in the overall behavior. To reveal occurring flow phenomena and physical effects, a scale-resolving hybrid RANS-LES simulation on a block structured mesh of about 400 million hexahedral elements of a double-regulated five-blade model Kaplan turbine is carried out. In this paper, first, the results of the ongoing simulation are presented. The major part of the simulation domain is running in LES mode and seems to be properly resolved. The validation of the simulation results with the experimental data shows mean deviations of less than 0.8% in the global results, i.e., total head and power, and a good visual agreement with the three-dimensional PIV measurements of the velocity in the cone and both diffuser channels of the draft tube. In particular, the trend of total head and the results for the draft tube differ significantly between the scale-resolving simulation and a standard RANS simulation. The standard RANS simulation exhibits a highly unsteady behavior of flow, which is not observed in the experiments or scale-resolving simulation. Full article

In this paper, an improved RSM-CFD method is used to optimally design a mixed turbine of non-equilibrium condensing steam (NECS) and hydrogen (H₂), of which the response surface method (RSM) and computational fluid dynamics (CFD) are coupled to take into account the effects of the wet steam non-equilibrium condensation process of the multimixed working fluid. A single-stage H₂/Steam (NEC)-mixed turbine was developed based on the improved RSM-CFD, and the effect mechanism of the H₂ component ratio (ω_H2) on the flow characteristics, internal power, and isentropic efficiency within the turbine stage were investigated. The results show that the isentropic efficiency (η) increases with the increase in the hydrogen component ratio (ω_H2), since hydrogen, as a non-condensable component, can inhibit the nucleation and growth of steam, reducing the pressure pulsation on the blade surface; furthermore, it accelerates the transport and diffusion of liquid droplets, inhibits the flow separation, and reduces the flow loss in the flow channel. However, the internal power of the turbine (P) tends to decrease with increasing ω_H2, since the increase in hydrogen reduces the pressure difference on the blade and lowers the torque of the fluid acting on the blade, and at the same time, the vortex and radial flow intensify, and the enthalpy drop inside the stage decreases. On this basis, the optimum operating conditions are found where the hydrogen component ratio (volume percent) ω_H2 = 53%. Accordingly, the hydrogen component ratio should be maintained in the range of 38–68%, considering the work capacity and hydrogen yield of the mixed working fluid. Full article

Turbulent flow, mainly originating from the rotor-stator interaction (RSI), is closely associated with the normal and safe operation of the centrifugal pump. In the current research, to clarify turbulent flow in the centrifugal pump with a vaned diffuser, the non-intrusive LDA (Laser Doppler Anemometry) system is applied to measure velocity pulsation signals at different regions when the pump operates at various flow rates. Time and frequency domain analysis methods are combined to investigate the velocity signals, and the velocity distribution around the volute tongue region is reconstructed from twenty measuring points. Results show that the velocity spectrum is characterized by the discrete components at the blade passing frequency and its higher harmonics, and it is caused by the RSI between the impeller and the diffuser. For the points in the volute spiral and diffusion sections, due to the significantly reduced RSI effect, the velocity spectrum shows an evident difference from comparison with the points between the impeller and diffuser, and the blade passing frequency is not always the dominant frequency. The comparison of velocity amplitudes and RMS* (root mean square of velocity) values at different points proves that the measuring position and flow rate affect velocity pulsations. As observed from velocity distribution reconstructed by LDA signals, high velocity regions are developed downstream of the diffuser channel for all the measured flow rates. Full article

In this study, we analyze gas–liquid interaction characteristics using a heterogeneous two-fluid model to investigate the influence of interphase force on multiphase pump performance. Two-phase transport platforms are used in oil and gas development to eliminate the need for separation equipment and reduce costs. Full-channel numerical calculations were conducted for an axial-flow multiphase pump based on different inlet gas void fractions (IGVFs) and flow rates. The results indicate that the interaction force of each phase is relatively large in the rotor–stator interference region, and the drag, lift, virtual mass, and turbulent dispersion forces increase with an increase in IGVF or when deviating from the design condition (Q = 50 m³/h). The interphase forces (resistance, lift, virtual mass force, and turbulent dispersion) increase considerably in the impeller passage and minimally in the guide blade passage. Under the conditions of small and high flows, the force of each phase changes considerably in the impeller and diffuser passages, respectively. Furthermore, the turbulent kinetic energy in the flow passage corresponds to the change trend of the interphase force, indicating that the interphase force causes energy loss inside a multiphase pump. These results provide essential information for the optimization of the hydraulic design of multiphase pumps. Full article

In centrifugal compressors, Mild Surge (MS) leads to unstable operation. Previous experimental work on a centrifugal compressor designed and built by Safran Helicopter Engines (SafranHE) showed that MS corresponds to the pulsation of an alternate stall pattern at the Helmholtz frequency of the test rig on two channels in the radial diffuser. The present contribution experimentally investigates the impact of the Inlet Guide Vane (IGV) stagger angle on this alternate flow and numerically studies the topology of this pulsating alternate flow. The experimental investigation is performed with unsteady pressure sensors, and shows that the IGV stagger angle only impacts the pulsation frequency of the alternate flow pattern. This change is explained by the dependence of the Helmholtz frequency on the compressor inlet section. The topological analysis of the average flow field, computed from wall-resolved Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations, demonstrates that the saddle point (major critical point) in the corner hub/suction side of the stalled blade migrates upstream while staying in the corner if the mass flow rate decreases. One main blade over two is stalled on both sides because the flow originating from this corner separation circumvents the trailing edge and migrates upstream along the pressure side. In the simulation, the pulsation of the alternate stall is coupled with the reflection of acoustic waves on the inlet and outlet planes, regarded as an environmental effect. Full article

Regulations from the European Union move towards a constant reduction of pollutant emissions to match the single-digit goal by 2050. Original equipment manufacturers propose newly designed components for the lifetime extension ofgGas turbines that both reduce emissions and allow for increasing thermodynamic performance by redesigning turbine cooling geometries and optimizing secondary air systems. The optimal design of internal cooling geometries allows for reducing both blade metal temperature and coolant mass-flow rates. In the present study, four different geometries of the region upstream from the blade’s internal cooling channels are investigated by using computational fluid dynamics with a conjugate heat transfer approach. The baseline configuration is compared to solutions that include turbulators, vanes, and a diffuser-like shapes. The impact of each solution on the blade metal temperature is thoroughly analysed. The diffuser-like solution allows for a more uniform distribution of the coolant and may reduce the metal temperature by 30% in the central part of the blade. There are also regions where the metal temperature increases up to 15%, thus requiring a specific thermal fatigue analysis. Eventually, the non-negligible impact of the coolant flow purged in the tip clearance region on the generation of the tip leakage vortex is described. Full article

In order to improve hydraulic efficiency, influence of inlet angle, outlet angle, wrap angle, inlet shape and outer edge camber lines of channel-diffuser blades on the energy performance of a three-stage centrifugal pump were studied and the pressure distributions on the blade of the first-stage channel-diffuser were particularly analyzed. The result shows that the efficiency of the pump is maximal when the blade inlet angle is 12°. The pressure variation in the model with the inlet angle of 12° was small and the amplitude of fluctuation was also not large. When the outlet angle was 90°, the pressure distribution in the outlet of the blades that are symmetrically distributed along the center of the diffuser shell was significantly better than that with other outlet angles. The effect of the blade wrap angle of the channel-diffuser on the energy performance of the pump was relatively small. The internal flow in the diffuser with the diffusion inlet shapes was steady for both the convex surface and concave surface. The diffusion inlet of the channel-diffuser blade corresponded to the outlet region of the impeller blade, which reflected a good matching. The fluctuation amplitude and the distribution range of the models with a uniform transition were smaller than those with non-uniform transition. In order to verify the effectiveness of the research results, an experimental test was carried out on the pump. The results show that when the flow rate is 850 m³/h, the head of the pump is 138.67 m and the efficiency of pump is 69.48%. Full article

For the purpose of improving the transport capability of the mixed transport pump, a new self-made three-stage deep-sea multiphase pump was taken as the research object. Based on the Euler-Euler heterogeneous flow model, liquid (water) and gas (air) are used as the mixed media to study the external characteristics and internal flow identities of the mixed pump under different gas volume fraction (GVF) conditions. According to the simulation results, a local optimal design scheme of the diversion cavity in the dynamic and static connection section is proposed. The numerical results before and after the optimization are compared and analyzed to explore the effect of the diversion cavity optimization on the performance, blade load and internal flow identities of the pump. The results show that the head and efficiency are obviously improved when the inner wall of the diversion cavity is reduced by 4 mm along the radial direction. After optimization, under the condition of 10% gas content, the head and efficiency is increased by 3.73% and 2.91% respectively. Meanwhile, the hydraulic losses of the diversion cavity and diffuser are reduced by 9.11% and 4.32% respectively. The gas distribution in the impeller is improved obviously and the phenomenon of a large amount of gas phase accumulation is eliminated in the channel. In addition, the abnormal pressure load on the blade surface is eliminated and the turbulent flow energy intensity is reduced. The average turbulent kinetic energy ( ${\mathrm{T}}_K$ ) at i = 0.51 of the first stage impeller passage is reduced by 35%. Finally, the reliability of the numerical method is verified by the experimental results. To sum up, the performance and internal flow identities of the optimized mixed transport pump are improved, which verifies the availability and applicability of the optimization results. This provides a reference for the research and design of a multiphase mixed transport pump in the future. Full article

This work aimed to study the bubble distribution in a multiphase pump. A Euler-Euler inhomogeneous two-phase flow model coupled with a discrete particle population balance model (PBM) was used to simulate the whole flow channel of a three-stage gas-liquid two-phase centrifugal pump. Comparison of the computational fluid dynamic (CFD) simulation results with experimental data shows that the model can accurately predict the performance of the pump under various operating conditions. In addition, the liquid phase velocity distribution, gas-phase distribution, and pressure distribution of the second stage impeller at a 0.5 span of blade height under three typical working conditions were compared. Results show that the region with high local gas volume fraction (LGVF) mainly appears on the suction surface (SS) of the blade. With the increase in inlet gas volume fraction (IGVF), vortices and low velocity recirculation regions are generated at the impeller outlet and SS of the blade, the area with high LGVF increases, and gas–liquid separation occurs at the SS of the blade. The liquid phase flows out of the impeller at high velocity along the pressure surface of the blade, and the limited pressurization of fluid mainly happens at the impeller outlet. The average bubble size at the impeller outlet is the smallest while that at the impeller inlet is the largest. Under low IGVF conditions, bubbles tend to break into smaller ones, and the broken bubbles mainly concentrate at the blade pressure surface (PS) and the impeller outlet. Bubbles tend to coalesce into larger ones under high IGVF conditions. With the increase in IGVF, the bubble aggregation zone diffuses from the blade SS to the PS. Full article