Ultra-low Specific Speed Research Articles

Experimental study on hydraulic performance optimization of ultra-low specific speed centrifugal pump

To improve the head and efficiency performance of an ultra-low specific speed centrifugal pump, this paper takes a marine magnetic-driven ultra-low specific speed centrifugal pump with a specific speed of 27 as the object of study. On the basis of the original model impeller with three blades, impeller A and impeller B with four blades of the same outer diameter and outlet widths of 4 and 2.5 mm were optimized and designed. Taking methanol as the medium, the impacts of factors such as the structure of the impeller, the aperture diameter of the throttling ring, and the cutting impeller outer diameter on the hydraulic performance of the ultra-low specific speed centrifugal pump are investigated. The influence of impeller structure, throttle ring aperture, cutting impeller outer diameter, and other factors on the hydraulic performance of an ultra-low specific speed centrifugal pump was explored. The study shows that the flow condition range of the original model impeller pump is very small, and the head decreases very fast, which cannot meet the design requirements; the head and efficiency of impeller A and impeller B are generally improved, but the flow or head deviates from the design condition, so it is necessary to set up a throttling ring or cut the outer diameter of the impeller to regulate the pump's operating parameters. The pump outlets were set up for the 12 and 15 mm inner diameter of the throttle ring and no throttle ring, respectively. Comparative experiments show that impeller A in the design head point using three kinds of throttle ring structure and the pump flow is greater than the design value of impeller B in the throttle ring bore diameter of 15 mm and that the pump flow and head can be achieved at the same time as the design value.

Study on the energy conversion characteristics in the impeller of ultra-low specific speed pump as turbine

Study on the energy conversion characteristics in the impeller of ultra-low specific speed pump as turbine

Influence Analysis of Runner Inlet Diameter of Hydraulic Turbine in Turbine Mode with Ultra-Low Specific Speed

The hydraulic turbine in turbine mode (HTTM) with an ultra-low specific speed (HTTM-ULSS) has the advantages of a simplified structure, high efficiency, and good stability and has great application value in the industry. However, the influence of the runner inlet diameter (D1) on the performance of HTTM-ULSS has not yet been fully studied. Therefore, the three-dimensional models of Francis runners were established in the ultra-low specific speed range by examining D1 = 0.49 m, 0.5 m, and 0.51 m, and the two-stage hydraulic turbine models were constructed with flow passage components. Then, internal flow and energy characteristics were calculated using Fluent 16.0 software. Further, the influence of D1 on HTTM performance was studied by comparing numerical simulation results. The results show that the water head of the HTTM-ULSS can reach 540.87 m when D1 = 0.51 m, showing its powerful ability to recover the pressure energy in high-pressure water. Moreover, the head and efficiency are closely related to D1; when D1 increases, the circulation at the runner inlet increases, resulting in an enhancement in the ability to recover the water head and decreases in efficiency and in the operating range of the high-efficiency zone; with D1 increasing, the flow pattern inside the runner becomes better, but the high-pressure area of the blade increases. When selecting the D1, attention should not only be paid to the ability to recover the water head but also to the pressure of the runner blades and the internal water flow pattern.

Study on the energy loss characteristics of ultra-low specific speed PAT under different short blade lengths based on entropy production method

With the increasing attention to micro-hydro power, the PAT has a broad prospect in micro-hydro power generation because of its low cost and simple structure. The ultra-low specific speed pump as turbine (USSPAT) is widely used in remote areas to realize micro-hydro power generation because of its advantages, such as high output power under a small flow rate. However, the output power of USSPAT is closely related to the length of the short blade. Therefore, this paper optimizes the design of USSPAT and selects four groups of short blades for the numerical simulation of energy loss characteristics of the USSPAT based on entropy production theory. Unlike other fluid machinery, the entropy production of USSPAT increases with the flow rate increase, so it has certain limitations to measure the energy loss of USSPAT under different flow rates simply by entropy production method. Therefore, the power loss number is defined in this paper to characterize the energy loss characteristics of PAT at different flow rates. The energy loss in the impeller is always the largest under all flow rate conditions, but at 0.4Qdes, the energy loss in the chamber is the largest. The length of the short blade mainly causes the change of entropy production in the downstream region at large flow rates. In contrast, at small flow rates, the entropy production in the upstream region changes the most. In addition, it is also found that the determination of the optimal Rs can effectively suppress the incident loss in the impeller inlet and the high wall shear in the local regions. As a result, to improve the performance of the USSPAT, it is necessary to consider the length of short the blade as an essential parameter. This study not only reveals the energy loss characteristics of the USSPAT, but also provides a new perspective for optimizing the USSPAT structure.

Study on the energy conversion characteristics in the impeller of USSPAT based on velocity triangle space decomposition

With the development of micro-hydropower generation, traditional pump as turbine (PAT) is difficult to meet the needs of micro-hydropower for developing dispersed and small-flow water resources. Ultra-low specific speed pump turbine (USSPAT) has broad prospects in micro-hydropower generation in remote mountainous areas due to its advantages of larger output power at a small flow rate. In this paper, the dimensionless number ξ to measure the power output capacity of the fluid particle ξ is proposed based on the velocity triangle space decomposition. The impeller is the only energy conversion component in (USSPAT). The study of ξ in the impeller of USSPAT found that the area with the largest output power of the impeller is mainly concentrated in the area with a larger impeller radius, and the overall power output of the impeller increases with the increase of flow rate. The local high-speed jet formed by the rotor-stator interaction (RSI) between the impeller and the volute at the inlet of the region S is the fundamental reason for the NP and jet-wake phenomenon in the impeller. W* = 0.9 is the critical value of NP in region S. The jet wake formed in region A makes the critical value of the region decrease along the flow direction. Therefore, the region A is the core region of the NP inside the impeller. In addition, the secondary flow at the impeller outlet is the main reason for the NP in this region. In addition to 0.6Qd, the secondary flow intensity increases with the increase in flow rate, and WLF inhibits the secondary flow intensity in the wear ring area. However, at a small flow rate (0.6Qd), the WLF gradually enters the mainstream, which weakens the inhibition of the secondary flow in the wear ring region and promotes the secondary flow intensity in the downstream.

Experimental Study of the Influence of the Geometrical Parameters of the Radial Labyrinth Pump on the Pump’s Operating Parameters and Performance

Centrifugal pumps are the most common machines responsible for the increase in hydraulic energy in a piping system. Their proper design, operation, and maintenance have a strong influence on the performance of technological processes carried out in many industrial units. For the ultra-low specific speed (nq < 10) application, there is no economical reason for these pumps to be used. This is caused by an increase in internal losses in the pump. The article concerns the problem of the hydraulic operation of a new type of labyrinth pump—the radial labyrinth pump (RLP), which is a developed axial unit. The main research method involves the experimental research of hydraulic sets consisting of passive and active discs. The analyses were preceded by dimensional analysis and experimental planning. The study investigates the influence of a chosen structural parameter of both discs on the process of energy conversion obtained in the pump. The influence of parameters such as number, depth and width of the grooves, as well as inlet angle and diameter on the properties of the pump was studied and discussed in detail. The essential novelty of the article is the recognition of the hydraulic performance of the RLP with grooved discs. To extend the scope of the conducted research for the chosen hydraulic sets, a comparison of the mutual cooperation of an active disc with a smooth and grooved passive one was conducted. It was identified that not every geometric relationship of the parameters of the active and passive discs results in an increase in head with respect to cooperation with a smooth passive disc (motionless). The highest head and high efficiencies were obtained for sets with short channels with large inlet diameters—zk12 and zk13—ratios for zk12 d1ap/d2ap = 0.78, and for zk13 zk12 d1ap/d2ap = 0.81. Based on the obtained results, preliminary recommendations for the construction were made.

Optimization of geometric parameters of hydraulic turbine runner in turbine mode based on the orthogonal test method and CFD

The hydraulic turbine in turbine mode (TMHT) with ultra-low specific speed is a new type of energy recovery device for recovering energy stored in the high-pressure fluid. In order to solve the problem of insufficient consideration of runner geometric parameter optimization, this paper proposes an optimization strategy (OT-CFD), which is based on the orthogonal test method and computational fluid dynamics (CFD), to optimize the performance of the TMHT runner. Firstly, the orthogonal test schemes are established with 5 levels of runner inlet diameter, outlet diameter, inlet height, blade inlet angle, and blade number. Then 25 three-dimensional models of two-stage TMHT containing flow passage components such as Francis runner are built. Further, the internal flow characteristics and energy characteristics of TMHT are calculated and then verified by the real machine test. By comparing the numerical simulation results, the design schemes of runner geometry parameters corresponding to the highest head (H) and the highest efficiency (η) are determined, respectively. On this basis, the optimization effect of runner geometry parameters is analyzed by numerical simulation based on CFD. In conclusion, the inlet angle is the most important factor affecting the efficiency, and the runner inlet diameter is the most important factor affecting the water head. Compared with the comparison scheme, the optimal η scheme has a more stable flow pattern, which provides an efficiency increase of 10.9%, a water head increase of 26.75 m, and a power increase of 646.32kW, greatly reduces the energy loss in the process of residual pressure recovery; the optimal H scheme has an efficiency increase of 2.61%, but more stable and regular flow pattern. More importantly, the optimal water head scheme, which has a water head increase of 185.53 m and a power increase of 1518.3kW, greatly increases the capacity of recovering the water head.

Development of Ultra-Low Specific Speed Centrifugal Pumps Design Method for Small Liquid Rocket Engines

With the growth of the satellite industry, the demand for a propulsion system for small launch vehicles and spacecraft has increased. Small liquid rocket engines may require Ultra-Low specific speed centrifugal pumps due to the low required thrust and volumetric flow rate and high combustion chamber pressure. Therefore, in this study, a design method of Ultra-Low specific speed centrifugal pumps for several hundred Newton class small liquid rocket engines was developed by combining various empirical formulas. In addition, centrifugal pump impellers were designed using the Stepanoff method, which is typically used in pump design, and the circular arc method. The most appropriate method for designing Ultra-Low specific speed centrifugal pumps was determined through a comparative analysis with other methods and validated through CFD. As a result, the pump designed using the proposed method exhibited a performance of pumping and suction superior to the Stepanoff method. Although the number of arcs did not considerably influence the pump performance, the single arc method was confirmed to be the most appropriate design approach in terms of the design productivity and simplicity.

Effect of blade width on ultra-low specific speed axial turbines

ABSTRACT Ultra-low specific speed axial turbines for cooling tower have some issues, such as low head, low efficiency, and turbulent internal flow. According to the orthogonal experiment and CFD analysis, it was found that the blade width was the main factor affecting the head, while the numbers of stay vanes and blades were the main factors affecting the efficiency. To further optimize the hydraulic performance of ultra-low specific speed axial turbines, six models of ultra-low specific speed axial turbines with different blade widths were designed. CFD numerical simulations showed that at different flow rates, with increasing blade width, the head gradually decreases and the efficiency shows a trend of first increasing and then decreasing. For the ultra-low specific speed axial turbine designed in this paper, when the blade width is 35 mm, the water head is 6.75 m, which meets the requirements of cooling tower turbines on head. At this blade width, the turbine achieves the highest efficiency of 81.15%, its flows are uniform, performance is stable. The internal flow field and pressure distribution of the runner are in better agreement with the design indexes of an ultra-low specific speed axial turbine. Thus, a high-efficiency ultra-low specific speed axial turbine suitable for cooling tower residual energy recovery is preferably selected.

Review of the Hydraulic and Structural Design of High-Speed Centrifugal Pumps

In recent years, much attention has been paid to the application of high-speed centrifugal pumps; still, the development of this pump faces several challenges. In order to obtain a more comprehensive understanding of the high-speed centrifugal pump, this paper reviewed the engineering application, technical challenges, and feasible solutions of this pump from the aspects of hydraulic design, including cavitation, hydraulic excitation, efficiency issue at an ultra-low specific speed, and the solution to these problems. The current state of the structural design of the high-speed centrifugal pump was briefly described in addition. For the faults in the existing high-speed centrifugal pump, some research studies on pump monitoring were presented. Finally, the status and shortcomings of the design of the pump were simply analyzed and summarized. It is hoped that this study can provide some references for the design and practical usage of high-speed centrifugal pumps.

Effect of Inlet Section of Circular Section Spiral Case on Performance of Ultra-Low Specific Speed Diagonal Flow Turbine

Variation of section area at volute inlet is a key factor affecting turbine performance. By changing the inlet section of the turbine volute, the inlet angle of the guide vane is changed, so the guide vane parameters will also be changed, which will affect the turbine performance. In order to study the influence of different volute inlet section areas on the overall hydraulic performance of ultra-low specific speed diagonal flow turbine, this paper redesigns the volute inlet section area of an ultra-low specific speed diagonal flow turbine. On the premise of applying the same runner, seven different volute inlet circular sections are designed. The numerical simulation of the full flow channel is carried out for each scheme, and the influence of inlet circular section area of different volutes on hydraulic performance of the ultra-low specific speed diagonal flow turbine is analyzed and compared. The results show that with the increase of flow rate, the calculated head and runner loss of the turbine increase, and the hydraulic efficiency of the turbine first increases and then decreases. When the turbine runs under small flow conditions (less than rated flow), the hydraulic efficiency of the turbine increases with the decrease of the diameter of the inlet circular section of the volute. When the turbine operates under high flow condition (greater than rated flow), the hydraulic efficiency of the turbine decreases with the decrease of the diameter of the inlet circular section of the volute. Through comparative analysis of seven schemes, the optimum radius of the inlet circular section of volute for the ultra-low specific speed diagonal flow turbine is 127mm and the corresponding inlet angle of guide vane is 32°. At this time, the efficiency of the turbine is 81.59% and the calculated head is 4.821m. The flow pattern inside the turbine is more uniform without whirlpools. It provides a reference for future design of similar type turbines and selection of suitable volute inlet circular section area.

Optimization Design of the Impeller Based on Orthogonal Test in an Ultra-Low Specific Speed Magnetic Drive Pump

To improve the hydraulic performance in an ultra-low specific speed magnetic drive pump, optimized design of impeller based on orthogonal test was carried out. Blades number Z, bias angle in peripheral direction of splitter blades θs, inlet diameter of splitter blades Dsi, and deflection angle of splitter blades α were selected as the main factors in orthogonal test. The credibility of the numerical simulation was verified by prototype experiments. Two optimized impellers were designed through the analysis of orthogonal test data. The internal flow field, pressure fluctuation, and radial force were analyzed and compared between optimized impellers and original impeller. The results reveal that impeller 7 (Z = 5, θs = 0.4θ, Dsi = 0.75D2, α = 0°) could increase the head and efficiency, compared to the original impeller, by 2.68% and 4.82%, respectively. Impeller 10 (Z = 5, θs = 0.4θ, Dsi = 0.55D2, α = 0°) reduced the head by 0.33% and increased the efficiency by 8.24%. At design flow rate condition, the internal flow of impeller 10 was the most stable. Peak-to-peak values of pressure fluctuation at the volute tongues of impeller 7 and impeller 10 were smaller than those of the original impeller at different flow rate conditions (0.6 Qd, 1.0 Qd and 1.5 Qd). Radial force distribution of impeller 10 was the most uniform, and the radial force variance of impeller 10 was the smallest.

Analysis of the influence of a stator type modification on the performance of a pump with a hole impeller

Abstract The article presents the results of numerical analyses and experimental research of the influence of various types of stators on a liquid flow through a centrifugal pump with a hole impeller. It is a continuation of authors research of cooperation pump stators with alternative types of impellers which work in ultra low specific speed. Hole impellers have become a significant alternative to classical ones in a range of extremely low specific speed n q <10. The aim of the research is to verify the quality as well as quantity of computer modeling results, and to estimate accuracy by examining the impact of a grid and a turbulence model with which the numerical simulations reflect the actual flow.Knowledge concerning construction of hydraulic elements of centrifugal pumps working in the range of parameters corresponding specific speed (n q <10) is insufficient. The outlet elements were tested in various configurations of constructional features. The complexity of the construction of the stator can significantly affect the manufacturing costs of pump unit.

Investigations of drilled and multi-piped impellers cavitation performance

Abstract The industry needs the rotodynamic pumps operating with ultra-low specific speed and relatively low flow rate more often. Designing of such structures on acceptable efficiency level is extremely difficult and require nonstandard approach to design as for example: drilled impeller or patented by author multi-piped impeller. Such pump elements are very easy to manufacture and operate with relatively high efficiency, but cavitation behavior is unknown. This paper focuses on experimental research in order to determine the cavitation characteristics of the drilled impellers and multi-piped impellers. The test rig was presented. Impeller models were made by means of SLS Rapid Prototyping methods. Additionally, CFD calculations were presented in order to determine static pressure distribution in the inlet sections of the investigated impellers.

Performance Analysis of a Multistage Centrifugal Pump Used in an Organic Rankine Cycle (ORC) System under Various Condensation Conditions

In an organic Rankine cycle (ORC) system, the working fluid pump plays an important role in the system performance. This paper focused on the operating characteristics of a multistage centrifugal pump at various speeds and condensation conditions. The experimental investigation was carried out to assess the influence of the performance of the pump by the ORC system with special attention to actual net power output, thermal efficiency as well as back work ratio (BWR). The results showed that an increase in the pump speed led to an increase in the mass flow rate and expand in the operating range of the outlet pressure. The mass flow rate decreased nonlinearly with the increase of the outlet pressure from 0.22 to 2.41 MPa; the electric power consumption changed between 151.54 and 2409.34 W and the mechanical efficiency of the pump changed from 7.90% to 61.88% when the pump speed varied from 1160 to 2900 r/min. Furthermore, at lower pump specific speed the ORC system achieved higher thermal efficiency, which suggested that an ultra-low specific speed pump was a promising candidate for an ORC system. The results also suggested that the effects of condensation conditions on the pump performance decreased with the pump speed increasing and BWR was relatively sensitive to the condensation conditions, especially at low pump speed.

Comparative research on various turbulence closure models for unsteady cavitation flows in the ultra-low specific speed centrifugal pump

This paper is aimed to develop a numerical framework for simulating unsteady cavitating flows in the ultra-low specific speed centrifugal pump. Various turbulence models, including RNG (Re-Normalization Group) k-ε model, SST (Shear Stress Transport) k-ω model and FBM (Filter-Based model), were modified by density correction and applied to predict explicit performances, cavitating and pressure fluctuation characteristics of an ultra-low specific speed centrifugal pump. Afterwards, comparisons were made with experimental visualization and measurement results and the numerical results among those models. It can be concluded that the modified turbulence viscosity can fit well with the hydraulic performances measured by the experiment, but the unsteady characteristics of the cavity shapes and pressure fluctuation were predicted well only by filter-based density corrected model (FBDCM), which take the local meshing resolution into consideration. Lastly, a global sensitivity analysis was conducted to assess the limitation of the filter size λ. The results indicate that when λ is less than 3 times the largest grid size, the numerical framework has a reasonable overall predictive capability, and it is expected to choose large value of λ for the computational efficiency.

Optimal hydraulic design of an ultra-low specific speed centrifugal pump based on the local entropy production theory

The ultra-low specific speed centrifugal pump has been widely applied in aerospace engineering, metallurgy, and other industrial fields. However, its hydraulic design lacks specialized theory and method. Moreover, the impeller and volute are designed separately without considering their coupling effect. Therefore, the optimal design is proposed in this study based on the local entropy production theory. Four geometrical parameters are selected to establish orthogonal design schemes including blade outlet setting angle, wrapping angle volute inlet width, and throat area. Subsequently, a 3D steady flow with Reynolds stress turbulent model and energy equation model is numerically conducted and the entropy production is calculated by a user-defined function code. The range analysis is made to identify the optimal scheme indicating that the combination of local entropy production and orthogonal design is feasible on pump optimization. The optimal pump is visibly improved with an increase of 1.08% in efficiency. Entropy production is decreased by 16.75% and 6.03% in impeller and volute, respectively. High energy loss areas are captured and explained in terms of helical vortex and wall friction, and the turbulent and wall entropy production are respectively reduced by 3.82% and 14.34% for the total pump.

A highly efficient Francis turbine designed for energy recovery in cooling towers

In China, cooling water entering cooling towers still retains surplus pressure between 39,240 and 147,150 Pa. In order to utilize this wasted energy, it is suggested that the surplus water energy can be harnessed to drive a type of hydroturbine installed in the inner platform of cooling tower and make the fan rotate via its coupled shafts. However, conventional hydroturbines are not suited for this job because of their low efficiency or unmatched rotating speed with that of the fan under the operating conditions of cooling towers. In this article, according to the requirements of turbine work environment in cooling towers, a new type of hydroturbine, Francis turbine with ultra-low specific speed ( ns = 50 m.kW), was designed to replace the fan motor in a cooling tower. Primarily, the shape, position, and number of runner blades were designed and optimized through theoretical analyses and computational fluid dynamics simulations. Additionally, metal elliptical volute and single-row ring guide vanes were applied to scale down the structural dimensions. Finally, the optimal scheme of the new Francis turbine was proven to have a high efficiency of 88% and good operation stability through testing of a physical model and can achieve the goal of harvesting renewable energy in the cooling tower.

Investigating the impact of multi-piped impellers design on the efficiency of rotodynamic pumps operating at ultra-low specific speed

Multi-piped impellers (name proposed by the author) represent an innovative approach to the design of rotodynamic pumps operating at the specific speed of nq<10. In such a construction the energy increase is caused by the flow of liquid through the internal impeller passages as well as by an external flow around the passages, and sensible designing of such a construction is extremely difficult. The study investigates the impact of the basic construction parameters of a multi-pipe impeller on the efficiency of the process of energy transfer into liquid. The main research method involves computational fluid dynamics (CFD) simulations. The selected impeller constructions are made with the SLS (rapid prototyping) method and tested with a measurement stand. The paper presents the comparison of numerical and experimental results. Based on the obtained results the author makes recommendations on the construction of multi-piped impellers.

The Operating Point Determination of Special Turbine in Cooling Tower

This article introduces the theory analysis and experimental study on the performance of special turbine in cooling tower. The author analyses the speed-flow characteristics of turbine-fan unit and the speed-flow characteristics of ultra-low specific speed turbine itself. At the same time the author points out the principles and methods to determine the best operating point of turbine-fan unit. So it is very important to determine whether the specific turbine is in the best condition.