Showing papers on "Diffuser (thermodynamics) published in 2019"
TL;DR: In this paper, the authors investigated the clocking position of the pump, defined as the circumferential position of vaned diffuser relative to the circular casing, to improve the hydraulic performance.
58 citations
TL;DR: In this paper, the complicated transient characteristics of gas-liquid two phase flow in a multiphase pump under 10% and 20% inlet GVFs are investigated by Dynamic Mode Decomposition.
47 citations
09 Jun 2019
TL;DR: In this paper, a numerical study of the influence of pressure fluctuations and unsteady flow patterns was undertaken in the pump flow channel of three configurations with different diffuser vane numbers, and the amplitude of pressure fluctuation in the diffuser was increased gradually with the increase in number of diffuser vanes.
Abstract: A pump is one of the most important machines in the processes and flow systems. The operation of multistage centrifugal pumps could generate pressure fluctuations and instabilities that may be detrimental to the performance and integrity of the pump. In this paper, a numerical study of the influence of pressure fluctuations and unsteady flow patterns was undertaken in the pump flow channel of three configurations with different diffuser vane numbers. It was found that the amplitude of pressure fluctuation in the diffuser was increased gradually with the increase in number of diffuser vanes. The lower number of diffuser vanes was beneficial to obtain a weaker pressure fluctuation intensity. With the static pressure gradually increasing, the effects of impeller blade passing frequency attenuated gradually, and the effect of diffuser vanes was increased gradually.
40 citations
TL;DR: In this article, the effect of a self-recirculation casing treatment device for suppressing various scales of flow instability has been discussed, and rig tests of a high pressure ratio centrifugal compressor were performed, and transient pressure signals were measured at endwalls by fast response pressure transducers.
38 citations
TL;DR: In this article, a combined pressure regulation solution is proposed to dredge the blocked entrained flow and alleviate the high pressure effect simultaneously for multiple optimization of the entrainment passage flow field.
23 citations
TL;DR: Results comparatively prove the energy dissipation mechanism in the centrifugal air pump under rotor-stator interaction and provide the quantitative basis for turbomachinery’s loss reduction design.
Abstract: In fluid machineries, the flow energy dissipates by transforming into internal energy which performs as the temperature changes. The flow-induced noise is another form that flow energy turns into. These energy dissipations are related to the local flow regime but this is not quantitatively clear. In turbomachineries, the flow regime becomes pulsating and much more complex due to rotor-stator interaction. To quantitatively understand the energy dissipations during rotor-stator interaction, the centrifugal air pump with a vaned diffuser is studied based on total energy modeling, turbulence modeling and acoustic analogy method. The numerical method is verified based on experimental data and applied to further simulation and analysis. The diffuser blade leading-edge site is under the influence of impeller trailing-edge wake. The diffuser channel flow is found periodically fluctuating with separations from the blade convex side. Stall vortex is found on the diffuser blade trailing-edge near outlet. High energy loss coefficient sites are found in the undesirable flow regions above. Flow-induced noise is also high in these sites except in the stall vortex. Frequency analyses show that the impeller blade frequency dominates in the diffuser channel flow except in the outlet stall vortexes. These stall vortices keep their own stall frequency which is about 1/5 impeller frequency with high energy loss coefficient but low noise level. Results comparatively prove the energy dissipation mechanism in the centrifugal air pump under rotor-stator interaction. Results also provide the quantitative basis for turbomachinery’s loss reduction design.
19 citations
TL;DR: In this paper, the authors investigated the performance of choked cavitating flow in a transparent venturi reactor at different pressure ratios by high speed camera technique and provided a thorough understanding of the evolution of cavitation regions, collapse mechanism, averaged wall pressure and pressure pulsation.
19 citations
TL;DR: In this article, a novel passive control method is proposed to mitigate the unsteadiness effects associated to the swirling flows with self-induced instabilities, which involves a progressive throttling cross-section flow at the outlet of the conical diffuser.
Abstract: In this paper, we introduce a novel passive control method to mitigate the unsteadiness effects associated to the swirling flows with self-induced instabilities. The control method involves a progressive throttling cross-section flow at the outlet of the conical diffuser. It adjusts the cross-section area with a diaphragm while maintaining all positions of the circular shape centered on the axis. It improves the pressure recovery on the cone wall while the pressure fluctuations associated with the self-induced instability are mitigated as it adjusts the cross-section area. It can adjust the diaphragm in correlation with the operating conditions of the turbine. We investigated the passive control method on a swirl generator, which provides a similar flow as a hydraulic turbine operated at a partial discharge. The plunging and rotating components are discriminated using the pressure fluctuation on the cone wall to provide a clear view of the effects induced by this passive control method. As a result, the novel proof of concept examined in this paper offers valuable benefits as it fulfils a good balance between the dynamical behavior and the hydraulic losses.
18 citations
TL;DR: In this article, the authors designed, built and evaluated the hydrodynamic performance of a sand filter diffuser plate using numerical simulations to maximize hydrodynamics efficiency during the filtration process and consequently minimise the effects of flow on the sand bed surface.
18 citations
TL;DR: In this article, a wet steam model has been proposed to enhance the understanding of the condensation and evaporation effects of water droplets from a numerical perspective, and the entire steam-ejector system including the nozzle, mixing chamber, throat and diffuser were modeled to study the profiles in axial pressure and temperature across the system, and were compared with self-measured experimental data.
Abstract: The steam ejector is a core component of an ejector-based refrigeration system. Additionally, steam ejectors can also be potentially applied for a fire suppression system by using pressurized steam droplets to rapidly quench and extinguish the fire. The use of steam will significantly reduce the amount of water consumption and pipe flow rate compared to conventional sprinklers. However, the efficiency of the steam ejector nozzle is one of major factors that can influence the extinguishing mechanisms and the performance of pressurized steam for fire suppression. In this article, to formulate an assessment tool for studying the ideal entrainment ratio and initial flow wetness, a wet steam model has been proposed to enhance our understanding of the condensation and evaporation effects of water droplets from a numerical perspective. The entire steam-ejector system including the nozzle, mixing chamber, throat and diffuser were modeled to study the profiles in axial pressure and temperature across the system, and were compared with self-measured experimental data. In addition, the flow and heat transfer interactions between the fluid mixture and nucleating water droplets were numerically examined by comparing initial conditions with different liquid fractions, as opposed to the ideal gas assumption. With the application of the proposed wet-steam model, the numerical model showed vast improvement in the axial pressure distribution over the ideal gas model. Through numerical conditions, it was found that reducing the wetness of the secondary inlet flow will potentially optimize the system performance with a significant increase of the entrainment ratio from 0.38 to 0.47 (i.e., improvement of around 23%).
17 citations
TL;DR: In this paper, a quasi-steady Blade Element Momentum model is used to predict instantaneous aerodynamic torque and power of wind and hydrokinetic turbines with diffusers, where the mass-moment of inertia of the entire system is taken into account, as well as the frictional losses in the bearings.
TL;DR: Investigation of cavitation characteristics of jet pump cavitation reactors with different throat lengths, throat types and diffuser angles suggests that throat structure plays a more important role in the cavitation and flow characteristics of JPCR when compared with diffuser structure.
TL;DR: In this article, the effect of the upstream buildings on the performance of a cross flow turbine was investigated by means of 2D CFD and the beneficial effect of a diffuser on the torque fluctuations damping was discussed.
TL;DR: In this paper, the authors designed a piezoelectric micropump using a combinational form of microvalves with sufficient diodicity in low-pressure gradients.
Abstract: The Present article aims to design a piezoelectric micropump using a combinational form of microvalves with sufficient diodicity in low-pressure gradients. The goal is to enhance the capability of piezoelectric micropumps with Tesla-type valves in order to deliver insulin. Tesla-type valves are in the category of passive valves which have sufficient diodicity in case of high-pressure gradients. However, low mass flow rates are often required in drug delivery devices. In this paper, the performance of MT135 Tesla-type valve in low pressure-gradient flows has been investigated and a range of reunion angles, which have not been studied before has been examined by numerical solutions. Inspired by nozzle-diffuser valve types, some changes in the bypass path of the microvalve have been exerted to boost the diodicity of the valve in low-pressure conditions that resulted in 9.97% increase of diodicity. At last but not least, the velocity gradients in singlephase flow of water has been attained and performance of micropump toward other kinds of flows has been investigated by a volume of fluid (VOF) model including water as the primary phase and air as the secondary one. To complete the analysis, a VOF model consisting of an arbitrary kind of Casson fluid with the primary phase of water was reached and discussed.
TL;DR: In this article, a conjugate heat transfer simulation of transient turbulent flow in a scaled turbine valve, which usually occurs in the fast start-up processes of coal-fired power plants, was performed against experimental validation.
TL;DR: In this article, the coupling between trapped vorticity and secondary flow vortices is manipulated using an array of fluidic oscillating jets, which are spanwise distributed just upstream of the trapped vortex.
01 Nov 2019
TL;DR: In this paper, the authors presented the results of mathematical simulation of the characteristics of a vane diffuser of a centrifugal compressor intermediate stage, such as the loss coefficient and the deviation angle versus the outlet vane angle of the diffuser.
Abstract: The paper presents the results of mathematical simulation of the characteristics of a vane diffuser of a centrifugal compressor intermediate stage, such as the loss coefficient and the deviation angle versus the outlet vane angle of the diffuser. The simulation of these characteristics was made on the basis of processing the results of studies performed by the Research Laboratory “Gas Dynamics of Turbomachines” of Peter the Great St.Petersburg Polytechnic University at the model characteristics of vane diffusers. Given the almost complete absence of recommendations in the literature, the paper describes the technology for constructing neural network models, which includes preparing a sample of input data and determining the optimal structure of the neural network. Based on the obtained mathematical models, a computational experiment was carried out in order to determine the influence of the main geometric and gas-dynamic parameters on the efficiency of vane diffusers. The results of the computational experiment on neural models of the efficiency of a vane diffuser are analyzed according to the existing ideas about the physics of the processes of energy conversion in a vane diffuser.
TL;DR: An approach for shape optimisation of the flow through a diffuser by simultaneously increasing the static pressure recovery across the geometry and the flow uniformity at the outflow using the Computational Fluid Dynamics software OpenFOAM.
Abstract: An approach for shape optimisation of the flow through a diffuser is presented in this work. This multi-objective problem focuses on maximising the diffuser performance by simultaneously increasing...
TL;DR: In this paper, the authors studied and analyzed the distribution and evolution of flow pattern under different flow, such as circulating-flow, through-flow and other forms, and built a model of flow patterns in the vortex pump, which has more perfectly fit the reality.
Abstract: The special structure of the vortex pump contributes to its complex internal flow pattern. A type of horizontal 150WX-200-20 vortex pump is taken as a research subject to deeply study the progression and distribution of flow pattern in its channel. To explain the mechanism of flow in this pump, numerical analysis of the whole flow and experiment have been conducted.,The authors studied and analyzed the distribution and evolution of flow pattern under different flow, such as circulating-flow, through-flow and other forms. Finally, a model of flow pattern in the vortex pump has been built, which has more perfectly fit the reality.,They are through-flow affected by circulating-flow, main and subsidiary circulating-flow, vortices between vanes and other vortices (or liquid impingement) in volute. Entering the pump, part of the flow stays in vanes and turn into vortices while the other goes into the front chamber. The flow that runs into the front chamber will be divided into two parts. One part will be collected by viscosity into a vortex rope when it passing through the interface between the impeller and the vaneless chamber, which closely relates to the circulating-flow, and the rest directly goes out of the field through the diffuser. Besides, a fraction of circulating-flow joins the through-flow when it goes through the section V and leaves the pump.,The research results build a theoretical foundation for working out the flow mechanism of the vortex pump, improving its efficiency and optimizing its hydraulic design.
TL;DR: In this article, a 2D CFD analysis of diffuser shape and yaw angle was carried out with focus on the effects of diffusers shape and wake characteristics, and the HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power (CP), torque ripple, overall thrust on diffuser and wake properties.
Abstract: With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. The HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power (CP), torque ripple, overall thrust on diffuser and wake characteristics. Slightly better CP were predicted for the symmetrical diffuser, due to the convergent walls that address the flow towards the blade with a greater attack angle during early and late upwind and to the viscous interactions between the turbine wakes and strong vortices shed by the diffuser. A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs. The insertion of a straight throat in the diffuser design proved to be an effective way to mitigate torque ripple, but a CP loss is expected.
TL;DR: In this article, a novel in-house designed non-axisymmetric vaned diffuser (NAVD) is applied in a centrifugal compressor, and experimentally analyzes influences of the NAVD on suppressing the flow instability and delaying the deep surge.
TL;DR: In this paper, the authors compared experimental static pressure measurement with CFD simulation in a centrifugal compressor at 12 points through the diffuser and found that the simulation results showed that the CFD model generally slightly underpredicts the static pressure value as compared to the experimental results.
Abstract: This paper compares experimental static pressure measurement with CFD simulation in a centrifugal compressor at 12 points through the diffuser. Three mass flow rates are selected, each for three operating speeds giving nine total operating conditions. The results show that the CFD model generally slightly underpredicts the static pressure value as compared to the experimental results. The discrepancy between experimental and numerical results ranges between -8% and +6% and is fairly consistent for a given operating condition, except for close to the blade trailing edge where the pressure variation is less regular and where the pressure is increasing most rapidly with radial position. In the consistent region, where the pressure gradient is low, the discrepancy is around two percent or less for simulations close to the design operating point. Away from the design operating point the errors increase up to approximately 5%. The simulation results were also used to investigate the effect of the position (from the blade trailing edge) of the impeller-diffuser interface (a characteristic of the frozen rotor simulation approach). Here an optimal position for the interface was found to be 2% of the blade radius. This value gave improved agreement with the experimental result in the initial region of the diffuser up to a distance of approximately 10% of the radius. At greater distances the position of the interface became less important. The results also highlighted a change in the pressure along the spanwise direction close to the tips. A dip in the pressure, which was observed in the experimental results, was only observed in the simulations close to the shroud. Close to the hub the simulation results recorded a small local peak. The simulation approach was then applied to further study the flow characteristics by examining the full-field velocity and pressure contours in the impeller and diffuser regions to identify changes due to the different operating conditions.
07 Feb 2019
TL;DR: In this article, an approach to investigate the complete pump characteristics by means of computational fluid dynamics (CFD) calculations is presented, with steady-state calculations and additional transient CFD investigations in the normal operating conditions, the whole pump characteristics were calculated accurately.
Abstract: Besides operating a centrifugal pump under normal conditions there are additional operating conditions possible; for example, a pump operated as turbine. Another example would be a pump trip where there are several abnormal operating conditions possible when the direction of flow and/or the direction of rotation are changing. The machine behavior in every possible operation condition can be represented by the complete pump characteristics, often called the 4-quadrant (4Q) behavior of a centrifugal pump. To gather the 4Q behavior, a test rig allowing the flow direction as well as the rotation direction to be reverted is necessary, with time-consuming measurements at variable positive and negative discharge in both directions of rotation the complete pump characteristics are evaluated. In the present study, an approach to investigate the complete pump characteristics by means of computational fluid dynamics (CFD) calculations is presented. With steady-state calculations and additional transient CFD investigations in the normal operating conditions, the whole pump characteristics were calculated accurately. Two different types of mixed flow diffuser pumps were investigated—one equipped with adjustable impeller blades, the second one with comparable low specific speed. Experimental verifications have shown a remarkably good agreement. Furthermore, an exemplary numerical waterhammer analysis shows the successful application of the presented approach.
TL;DR: In this paper, a transparent ejector is designed, fabricated, and operated using air as working fluid, and experimental studies have been conducted to depict the flow patterns in a small rectangular ejector by using schlieren flow visualisation technique.
01 Jan 2019
TL;DR: In this paper, the effect of different inlet swirl angles 0°, 7.5°, 12°, 17° and 25° has been studied to predict the reversal of flow and separation of flow from the wall.
Abstract: Annular diffusers are integral component of the axial flow compressor, combustion chambers and inlet portion of jet engine. In present study flow behavior inside the parallel hub and diverging casing annular diffuser having area ratio 2 to 4 with help of FLUENT has been predicted. The effect of different inlet swirl angles 0°, 7.5°, 12°, 17° and 25° has been studied to predict the reversal of flow and separation of flow from the wall. The result analysis shows that swirl enhances the pressure recovery up to a particular swirl angle and falls thereafter. It also helps in suppressing the flow separation. The effect of inlet swirl on the pressure recovery coefficient has also been figured out.
TL;DR: In this article, an experimental analysis of a second-throat exhaust diffuser (STED) performance has been conducted for the high altitude test of a parabolic bell-type nozzle.
TL;DR: In this paper, the authors used a control volume model to predict the flow parameters in key cross-sections of the injector working with maximum discharge pressure and temperature, and the proposed model results were compared with the measurements.
TL;DR: In this article, the mixing of two supersonic streams in a SU-personic exhaust diffuser using theoretical, numerical, and experimental approaches was investigated, and the effects of diffuser contraction ratio (CR) and convergence angle (θ) on the starting process, pressure recovery, and flow features were investigated.
TL;DR: In this paper, the effect of changes in the number of blades and the corresponding changes in cross throat area on the flow properties such as density and speed of sound were investigated and discussed.
TL;DR: In this paper, a guide-vane type augmentation is proposed, with a simpler outline and a better adaptability to various directions of the incident water flow, as compared to the duct-type diffuser.
Abstract: It is reported that the augmented vertical axis turbine (VAT) has a better operating performance. A guide-vane type augmentation is proposed in this study, with a simpler outline and a better adaptability to various directions of the incident water flow, as compared to the duct-type diffuser. A 2-D numerical model based on the computational fluid dynamics software ANSYS-Fluent is established and validated by experimental data. It is found that the guide vanes could narrow the flow path together with the VAT rotor and increase the flow velocity around the blades. The fluctuation of the instantaneous torque output is significantly reduced by using the guide-vane stator. The numerical results indicate that a four blades setup is suitable for the stator and the chord length of the guide vane should be equal to that of the rotor blade. The gap between the stator and the rotor is suggested to be a quarter of the chord length of the rotor blades. The non-zero pitch angle of the guide vane is found to have negative effects on the torque and the power output. The averaged power and torque coefficients for three non-zero directional angles of the incident flow are approximately 30% lower than those for the zero-directional angle.