Hydraulic Losses Research Articles

Validation through internal flow physics of response surface methodology optimized mixed flow pump as turbine

In order to determine the optimal working efficiency of mixed flow pumps as turbine (MF-PAT) under a design condition of 10m3kw, this study takes the number of blades, blade wrap angle, impeller outer diameter, and impeller inlet width as design variables. Based on the center combination design method, experimental scheme design is carried out, and the head, shaft power, and efficiency of the turbine are used as evaluation indicators. A response surface model is constructed for optimization analysis, and the optimal geometric parameter combination of the impeller for MF-PAT is determined. For MF-PAT with forward-curved blade impeller in this paper, the optimal parameter combination is recommended as blade number Z = 6, blade wrap angle α = 47°, impeller outer diameter D2 = 140 mm and impeller inlet width b2 = 34 mm. The results show that compared with the original scheme, its efficiency has increased by 7.8 %. The established response surface model can reflect the relationship between evaluation indicators and design variables, and can be used for optimizing the geometric parameters of MF-PAT impellers. It can effectively enhance the blade's constraint ability on liquid flow, reduce hydraulic losses, and improve the performance of MF-PAT. Apply the ns-ds methodology for this and future mixed flow optimized pumps as turbines.

Development of a horizontal seepage test system of constructed wetland and research on the seepage characteristics based on micro-pollution water

Horizontal subsurface flow constructed wetlands (HSFCW) were widely used as an effective biotechnology for wastewater treatment. However, clogging of the substrate bed was a key factor restricting its application. In this study, a horizontal seepage test system was independently developed, which was used to reveal the development trends of hydraulic resistance in HSFCW, as well as changes in permeability coefficients with time. The relationship between the average permeability coefficient and purification effect was further analyzed. The results showed that the new test system has proved the law of resistance development in HSFCW. The distribution characteristics of the isobaric surface indicate that the blockage of the HSFCW gradually spreads from the lower part to the lower part. The seepage resistance of homogeneous subbed in HSFCW was mainly concentrated in the front end. The growth rate of hydraulic loss in the core zone ranged from 0.685 to 19.515 cm·month−1, the growth rate in the transition zone ranged from 0.223 to 0.695 cm·month−1, and little change occurred in the safety zone. At the end of the HSFCW operation, the widths of the core, transition, and safety zones account for approximately 20–30 %, 50–70 %, and 10–20 % of the entire wetland length, respectively. Meanwhile, the SS removal rate stabilized at over 92 %, when the average permeability coefficient reached 41.45 m·d−1. The removal rate of COD and TN was higher when the average permeability coefficient is between 59.45 and 41.45 m·d−1 and 27.08–59.45 m·d−1, respectively. This study provided a horizontal testing method to accurately understand the changes in the seepage field in HSFCW.

Analysis of hydrofoil tip leakage vortex dynamic characteristics

The clearance exists inevitably between the turbine guide vanes and the fixed wall, and the resulting tip leakage vortex leads to the increase of hydraulic loss. Based on the fluid simulation software ANSYS CFX, the hydrofoil was numerically simulated under different flow velocity conditions. The trajectory and energy dissipation of the tip leakage vortex are discussed. The results show that the jet entrainment with the main flow to form the tip leakage vortex, which is mainly divided into main leakage vortex and separation vortex. The flow evolution of tip leakage vortex can be divided into three stages. The evolution of tip leakage vortex can be divided into three stages: independent development of main leakage vortex and separation vortex, fusion stage, and dissipation of main leakage vortex. The strongest turbulent kinetic energy dissipation occurs in the clearance, which confirms that the clearance causes non-negligible energy dissipation for hydraulic machinery. The results provide guidance for tip leakage vortex control of hydraulic hydrofoil.

Unidirectional Flow Through Time-Dependent Cross-Sectional Areas of a Compliant Tube and a Valve: A Nonlinear Model

This work investigates the conditions for net flow generation by a straight tube with a cross-sectional area harmonically varying in time that connects two tanks—a problem that is mainly found in the design of impedance pumps. By assuming a quasi-one-dimensional flow and applying continuity and momentum equations, a first-order differential equation with respect to the flow rate is derived and presented for the first time, including a nonlinear term that is responsible for net flow rate generation. Namely, the net flow rate is found to be nonzero (as is the nonlinear term) if the cross-sectional areas of the two tanks are unequal and one of them is smaller than that of the straight tube. In this case, the flow is directed from the smaller to the larger tank and the net flow rate increases with the frequency of the tube’s cross-sectional area variation. In contrast, when the tanks’ cross-sections are equal, the net flow is generated only if a valve is installed, e.g., at one end of the tube, due to the large asymmetries imposed in the hydraulic losses with respect to the tube mid-length. Compared with constant valve opening, the net flow rate is augmented significantly if the valve opening is time-dependent. By employing the same equation, the flow rate of an intra-aortic counter-pulsating balloon pump is also examined, in which the valve (representing the aortic valve) opens during the shrinkage of the tube, and it is shown that the net flow rate increases with the frequency and amplitude of the tube’s cross-sectional area. Conclusively, the harmonic oscillation in time of a tube’s wall can cause unidirectional flow only if asymmetric losses are present with respect to its mid-length.

Anomalous heat transfer enhancement in separated flow over a zigzag-shaped dense package of inclined grooves in a channel wall at different temperature boundary conditions

Rapid development of the anomalous enhancement of separated turbulent Re = 6000 air flow and heat transfer in an in-line single-row package of 31 inclined grooves, 0.2 in dimensionless depth, in a singled-out longitudinal region of the wall of a narrow channel is studied. It is due to the interference of vortex wakes behind the grooves and the acceleration in the channel flow core with the formation of a zone of ultrahigh longitudinal velocity. The wave-shaped parameter characteristics are stabilized in the region of approximately 15th groove, whereupon the oscillation amplitudes are moderately reduced. The return flows in the grooves are enhanced with distance from the entry section, the minimum negative friction diminishing from −2 to −4. The total relative heat removal from the structured region increases atq= const by a factor of approximately 2.75 and by the factor of two atT= const with increase in the relative hydraulic losses by the factor of 1.7, as compared with the case of a plane–parallel channel. The relative heat removal from the surface bounded by the contour of the 20th inclined groove amounts to 3.7 (q= const) with increase in the hydraulic losses by the factor of 2.2. An increase in the local maximum of the longitudinal velocity up to a factor of 1.5, as compared with the mean-mass velocity, can be observable.

Energy-saving mechanism and dynamic characteristics of blade angle adjustment in low head pumping system

To investigate the energy-saving mechanisms and dynamic characteristics of blade angle adjustment, this study proposes a novel research method via simulations, prototype and model testing. For stable conditions, the internal field, the external and energy characteristics of the pumping system with different blade angle are examined. The dynamic characteristics of the pumping system and the blade force characteristics during the adjustment process are also studied. The research results show that, under a certain net head, an appropriate impeller blade angle improves the flow state in the pump and conduits, decreasing the entropy production and providing suitable inlet circulation to reduce the hydraulic loss of outlet conduit, thereby improving the pumping system efficiency by 5–10 percentage points. During the adjustment process, there is an approximate 20-s delay in dynamic characteristics. Additionally, with the increase of the blade angle, the hydraulic torques for blade axis and pump shaft increase, thus increasing the blade adjustment force and shaft power. The adjusting force is found to be underestimated in the adjustment processes of decreasing the blade angle. Achievements of this paper contribute to high efficiency of pumping system and high reliability of blade adjustment devices and pump units.

Low-energy advanced wastewater treatment using submerged nanofiltration

The use of submerged nanofiltration (NF) membranes in wastewater treatment is an emerging process that produces high-quality recycled water with low energy consumption. This study aimed to identify the potential of coupling anaerobic digestion with this low-energy advanced wastewater treatment using submerged NF membranes. The direct NF of primary wastewater effluent using four types of commercial NF membranes resulted in progressive membrane fouling over 4 d. However, almost all the foulants contributing to hydraulic loss were removed by one-swipe sponge cleaning. This indicated that the major foulants were generally deposited on the membrane surface during direct NF. The membrane fouling speed varied during the long-term test depending on the feed wastewater quality. Although the transmembrane pressure increased by up to 50 kPa in every filtration cycle (4–7 d), sponge cleaning removed all the membrane foulants, resulting in >30 d of operation without chemical cleaning. The NF concentrates (four times concentrated wastewater) were then used for biogas production in an anaerobic digester. The volume of biogas formed from the NF concentrates sufficiently compensated for the energy consumption of direct NF. This study realized a low-energy advanced wastewater treatment utilizing NF concentrates that can also be used for biogas formation.

Investigation into the Energy Loss Mechanism of Pump Turbine During the Runaway Process Based on Entropy Production Theory

Abstract The power-trip of the pump under certain conditions leads to the runaway of the unit, causing dangerous transitional process in pumped storage power stations. This process is characterized by transient hydraulic features like flow separation and vortex structures, which increase hydraulic losses significantly and severely impact unit efficiency and stability. This paper aims to elucidate the mechanism of energy loss due to unstable flow during pump turbine runaway. It focuses on a high-head model pump turbine, examining the transient flow process from pump conditions to runaway conditions. It conducts quantitative analysis of energy loss using entropy production theory, besides, further clarifies the location and causes of hydraulic losses by integrating with internal flow analysis. The results show that a significant high-entropy production zone is captured in the pump braking condition, indicating extremely chaotic internal flow in this area during the runaway transition process. Additionally, throughout the transition process, turbulent entropy production initially increases, then decreases. Turbulent entropy production accounts for more than 80% of total entropy production, indicating that turbulent entropy production dominates throughout the entire transition process. The energy of the water is primarily dissipated within the runner during the runaway process. The maximum proportion is 87%, which is in the pump braking condition. Correlation analysis between flow and hydraulic losses reveals that vortex structure induced by flow separation under off-design conditions is the primary contributor to increased hydraulic losses.

Influence of axial distance between impeller and diffuser on the hydraulic performance and flow loss characteristics of bulb tubular pump

Abstract Bulb tubular pumps used in regional water transfer projects consume substantial power. Optimizing the geometric parameters of tubular pumps is crucial for enhancing efficiency and minimizing hydraulic losses. ANSYS CFX is used to investigate the axial distance between the impeller and the diffuser on the hydraulic performance and flow loss characteristics of the rear-bulb tubular pump, and the numerical simulation results are compared with the experimental data. Then, the entropy production theory is introduced to analyze flow losses. As the axial distance increases, the diffuser’s rectification effect on the flow at the impeller outlet deteriorates, leading to increased flow losses and decreased head and efficiency of the device. Flow losses in the bulb tubular pump are ranked from largest to smallest as follows: impeller, outflow channel, diffuser, inlet channel. The impeller exhibits the highest entropy production ratio, reaching 61.05% at an axial distance of 25 mm. By elucidating the energy loss distribution of each component under varying axial distances, this paper offers insights for the hydraulic optimization design of bulb tubular pumps.

Research on the hydraulic loss in the side inlet and outlet of a pumped storage power station

Research on the hydraulic loss in the side inlet and outlet of a pumped storage power station

Study on the influence of guide vane opening on pressure pulsation of pump-turbine under zero flow pump condition

Abstract Reversible pump-turbine is the key equipment of energy conversion in large pumped storage power station, and it is the core of stable operation of power station. Under the pump condition, the internal pressure pulsation law of the pump-turbine has an important influence on the stable operation of the pump. In order to study the pressure pulsation characteristics of pump-turbine in pump mode under zero flow condition, this study carried out unsteady numerical simulation on three kinds of guide vane openings, and analyzed the amplitude frequency characteristics of pressure pulsation in turbine under different head and the influence of internal flow characteristics on pressure pulsation. The research shows that in the pump mode, when the guide vane opening of the turbine increases, the influence of the blade frequency and the shaft frequency on the vaneless area increases, resulting in the maximum pressure fluctuation amplitude in the vaneless area under the pump condition, especially when GVO = 19 °. At the same time, due to the influence of dynamic and static interference, the larger turbulent kinetic energy appears in the vaneless area and the connection between the guide vane flow channel and the runner flow channel, resulting in an increase in hydraulic loss. Both the experimental and simulation results show that the guide vane opening of 19 ° should be avoided to reduce the hydraulic loss in the vaneless area when the turbine is operated under the zero flow pump condition.

Influence of Maximum Airfoil Camber Position on Hydrofoil Cavitation Performance

Abstract This study’s primary goal is to investigate how various airfoils’ maximum camber positions affect hydrofoil cavitation performance. Through numerical simulation, the cavitation low properties of hydrofoils with various maximum camber positions are compared. The accuracy of the modi ied turbulence viscosity and SST k-ω turbulence model on the temporal and spatial evolution characteristics of cavitation near the hydrofoil is evaluated by combining it with the model test. Analysis is done on the cavitation low ield of four airfoils at two distinct design angles of attack (+4° and +6°) with varying maximum camber locations (fmax = 35%C, 40%C, 50%C, and 60%C). The indings indicate that at 35%C, the hydrofoil’s maximum camber position has improved cavitation performance. The hydrofoil’s cloud cavitation evolution time is shorter than that of the original hydrofoil, and during the same time period, more cavitation is generated. The lift-to-drag ratio and lift coef icient of the cavitation low ield are signi icantly improved at both angles of attack. At the same time, the vorticity distribution and entropy generation distribution can be effectively reduced under the design angle of attack and high angle of attack cavitation, and the hydraulic loss in the cavitation low ield can be reduced. This research can serve as a guide for optimizing the hydrofoil’s cavitation performance and designing the impeller of the axial low pump that follows.

Investigation on the hydraulic loss in the vertical inlet and outlet of a pumped storage power station

Abstract The vertical inlet/outlet is commonly adopted in the upper reservoir of pumped-storage power stations, in which the internal flow patterns exert a critical influence on the safety and operational efficiency of the entire power station. Based on the standard k-ε turbulence model coupled with the revised wall roughness theory, this investigation presented a numerical model of a vertical inlet/outlet in a pumped-storage upper reservoir and the validity and accuracy of the numerical simulation are validated through comparison well with the results of the model experiments. The results suggest that the emergence of vortices of varying intensities near the inlet during power-generation scenarios at dead water levels and at 3.5 times of the rated flow rate (389.6 m3/s). The bend section experiences fairly nonuniform flow velocity, with the highest average flow hydraulic loss in the entire vertical pipe inlet/outlet system. These insights provide a substantial utility for operational strategies and optimization designs in related engineering projects.

CFD analyses and model tests for the optimization design of a large mixed-flow pumping system

Abstract Aiming at the optimization design of the pumping system with mixed-flow pumps, a serial of comparative hydraulic tests, numerical simulation and physical model tests were carried out. The comparative hydraulic test results of suction and discharge passages showed that the design scheme proposed by authors had better flow patterns and smaller hydraulic loss. The comparative CFD analyses indicated that the internal flow in the elbow-type suction box designed by authors were smoother and the flow conditions generated for pump were slightly better, but the flow distribution on both sides of partition pier in the siphon-type discharge passage was obvious poor compared with the scheme proposed by the contractor. Model tests were carried out respectively in the overseas and domestic and the model test results were basically consistent with those of numerical prediction, but the pumping system efficiency in high efficiency zone achieved in model tests was a litter lower than that by CFD. The optimized pumping system was characteristic of higher pumping efficiency and larger flow rate when operated at the designed conditions. The measuring results onsite shown that the best efficiency is more than 80% by use of the optimized pumping system installing mixed-flow pumps with guide vanes.

Analysis of the influence of different support types on the operation performance of bidirectional shaft tubular pump

Abstract Because of the particularity of the pump’s bidirectional operation, and the difference of the flow channels on both sides of the pump. The device has a mature impeller and guide vane combination when it is running forward. And when the device runs in reverse, the support on the shaft side acts as the rear guide vane of the impeller, which has great influence on the performance of the device. However, due to the few operating conditions in reverse operation, the importance of support is often ignored. In this paper, the influence of different support types on the bidirectional flow pattern and performance of the device is analyzed by numerical simulation. The results indicate that by optimizing the variation trend of the edge arc radius of the supporting baffle section, it is possible to effectively control the section with poor flow distribution, thereby reducing hydraulic losses. The support adopts three partitions arranged at an interval of 120°, which has little difference in performance during forward operation compared with other schemes. But during reverse operation, it reduces the impact and friction losses of water flow. And it fully utilizes the direct guide vane function of recovering vorticity, resulting in a significant increase in efficiency. At the same time, the accuracy of numerical simulation results is verified by model tests. The stability of positive and negative operating pressure pulsation supporting the inlet and outlet under the optimal scheme is analyzed.

Research on the internal flow characteristics of centrifugal pump based on streamlined anti-guide vane

Abstract Anti-guide vane is part of the radial guide vane in multi-stage centrifugal pump, and the hydraulic loss of anti-guide vane is the dominant factor affecting the performance of radial guide vane. In this paper, the radial guide vane is chosen as the research object, an optimization scheme of streamlined anti-guide vane is proposed based on the arc-shaped anti-guide vane with inlet angle α=25°. The simulation calculation of multi-stage centrifugal pump is drawn using the SST k-ω turbulence model. and the influence of the streamlined anti-guide vane on the hydraulic performance is studied. The result shows that: Under various flow conditions, the head of the multistage centrifugal pump with streamlined anti-guide vanes is higher than that of the prototype. When the flow rate is 1.3Q, the head is increased by 7.2%. and the efficiency is increased by 2.3%. The amplitude of pressure fluctuation of the streamlined anti-guide vane is significantly decreased at each monitoring point compared to the prototype, indicating that the streamlined anti-guide vane weakens the influence of the pressure fluctuation. Furthermore, the streamlined anti-guide vane enhances the pre-swirl of the inlet fluid to the secondary impeller, reduces the impact loss, and improves the pressurization capacity of the secondary impeller.

Application of drag reduction agents as a method for reducing heat loss during pumping through a pipeline

Relevance. The need to maintain the temperature regime of product pumping under increasingly complex conditions of pipeline routes by reducing heat losses of oil and petroleum product pipelines, as well as expanding the scope of application of anti-turbulence additives. Aim. To determine the effect of anti-turbulence additives on heat and hydraulic losses in the pipeline and to propose cost-effective ways to use additives when pumping through pipelines. Objects. Heat and hydraulic losses in pipelines pumping oil and oil products. Methods. Mathematical analysis of the influence of anti-turbulence additives on the thermohydraulic properties of the flow to assess the prospects for increasing the energy efficiency of pumping liquid through pipelines by introducing polymer additives. Results. The flow temperature was calculated using anti-turbulence additive depending on its concentration and efficiency, taking into account the dependence of the properties of the pumped product on temperature. The authors have constructed the graphic dependences of the economic components of heat and hydraulic losses on the concentration of anti-turbulence additives. The economic feasibility of the decision was estimated in terms of calculating the difference in pumping costs with and without anti-turbulence additives. The authors identified the relationship between the impact of losses from friction heat and heat exchange with the environment on heat losses, and analyzed the change in these parameters after the introduction of anti-turbulence additives. For the pipeline under consideration, the parameters of which correspond to standard pumping ones, the сonclusions were drawn on the predominance of the contribution of the additive hydraulic efficiency over the thermal one. This indicates the advisability of using an anti-turbulence additive as an agent for reducing heat losses at high values of the efficiency of the polymer additive, however, the overall economic efficiency is maximum at lower concentrations of the agent. The authors constructed a planar graph reflecting the dependence of the temperature at the end of the pipeline section on two coordinates: the length of the section and the hydraulic efficiency of the introduced additive.

Efficient Pump Scheduling for Large‐Scale Multiproduct Pipelines Using Deep Reinforcement Learning

ABSTRACTOptimizing pump scheduling in multiproduct pipelines can significantly reduce energy consumption and carbon emissions. For pump scheduling in multiproduct pipelines, to describe hydraulic losses more accurately, the model needs to adopt shorter discrete time intervals, which will lead to longer decision‐making time. It combined with the large solution space of large‐scale pipelines, will lead to low solution efficiency with dynamic programming methods and poor solution quality with heuristic optimization algorithms. Given that, this article develops a multiproduct refined oil transmission simulation system and employs the enhanced Proximal Policy Optimization (PPO) algorithm with action space shaping trick to optimize pump scheduling for large‐scale multiproduct pipelines. The method of converting discrete action space to multi‐discrete action space through action shaping can address PPO's low convergence efficiency issue resulting from the large discrete action space challenge common in large‐scale multiproduct pipelines. The experimental results indicate that the proposed method, that is, PPO algorithm with multidiscrete action space exhibits significant advantages in terms of efficiency and robustness in large‐scale pipelines compared to mainstream methods for pump scheduling such as dynamic programming (DP), genetic algorithms (GA), and ant colony optimization (ACO). Furthermore, we demonstrate the effectiveness of action space shaping in large‐scale pipelines from the perspectives of exploration and exploitation.

Numerical prediction of passive speed and performance for multistage pump without power drive in natural flow process

With the development of engineering applications and the increase in system complexity, some particular fields, such as liquid rocket engine turbopumps, aircraft engine fuel systems, and marine natural flow cooling systems, are increasingly focusing on the performance characteristics of pumps under natural flow conditions. The pump is in the form of resistance components under natural flow conditions without a power drive. The impeller undergoes passive rotation by the impact of inlet flow. Due to the specificity of its operating conditions and performance indicators, the pump's natural flow performance cannot be evaluated by regular methods. Therefore, this paper proposed a numerical prediction method for pump natural flow performance based on a coupled computational fluid dynamics coupled with six-degrees-of freedom model. The performance of a multistage pump with guide vanes was evaluated under different natural flow conditions, and the accuracy was verified by experimental measurements. The transient variation mode of pump performance parameters with time at the initial stage of natural flow impact was analyzed. The flow field's transient evolution characteristics and the wall shear stress variation during natural flow were investigated. It was found that the impeller's passive rotational speed increases linearly with the natural flow rate, while the hydraulic loss shows an exponentially increasing trend. Meanwhile, the natural flow loss coefficient shows an exponentially decreasing trend and gradually tends to a stable value. The high turbulent kinetic energy inside the impeller is mainly distributed in the flow separation region and large velocity gradients. The distribution of shear stresses is closely related to the flow behavior inside the pump and the geometrical features of the hydraulic components.

Rewatering after drought: Unravelling the drought thresholds and function recovery-limiting factors in maize leaves.

Drought and subsequent rewatering are common in agriculture, where recovery from mild droughts is easier than from severe ones. The specific drought threshold and factors limiting recovery are under-researched. This study subjected maize plants to varying drought degrees before rewatering, and measuring plant water status, gas exchange, hydraulic conductance, hormone levels, and cellular damage throughout. We discovered that stomatal reopening in plants was inhibited with leaf water potentials below about -1.7 MPa, hindering postdrought photosynthetic recovery. Neither hydraulic loss nor abscisic acid (ABA) content was the factor inhibited stomatal reopening on the second day following moderate drought stress and rewatering. But stomatal reopening was significantly correlated to the interaction between hydraulic signals and ABA content under severe drought. Extended drought led to leaf death at about -2.8 MPa or 57% relative water content, influenced by reduced rehydration capacity, not hydraulic failure. The lethal threshold remained relatively constant across leaf stages, but the recoverable safety margin (RSM), that is, the water potential difference between stomatal closure and recovery capacity loss, significantly decreased with leaf aging due to delayed stomatal closure during drought. Our findings indicate hydraulic failure alone does not cause maize leaf death, highlighting the importance of RSM in future research.