Transient Characteristics of Water-Jet Propulsion with a Screw Mixed Pump during the Startup Process

Han, Wei; Zhang, Teng; Su, You Liang; Chen, Ran; Qiang, Yan; Han, Yang

doi:10.1155/2020/5691632

Cited by 6 publications

(4 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Two grid interfaces were generated before the inlet and after the outlet of the impeller to simulate the flow field with dynamic and stationary interference. The Rayleigh-Plesset bubble dynamic homogeneous flow model was used to simulate the occurrence and collapse of cavitation [29]. The specific numerical simulation was performed in three steps: Firstly, the simulation of the steady flow field inside the high-speed pump-jet propeller was carried out, and the reference pressure was set as a standard atmospheric pressure; cavitation was not considered in the steady calculation.…”

Section: Boundary Conditionsmentioning

confidence: 99%

The Transient Characteristics of the Cavitation Evolution of the Shroud of High-Speed Pump-Jet Propellers under Different Operating Conditions

Gan,

Shi,

et al. 2023

Water

View full text Add to dashboard Cite

Pump-jet propellers are currently the mainstream propulsion method for underwater vehicles, and cavitation is an important factor limiting the high speed and miniaturization of pump-jet propellers. In order to explore the cavitation performance of high-speed pump-jet propellers, based on the modified SST turbulence model and the Zwart cavitation model, a three-dimensional numerical simulation of unsteady internal cavitation flow was carried out by comparing the impeller with specific speed ns = 1920 using FLUENT 2020R2 software. At the same time, the occurrence and development process of cavitation under 0.95 Q, 1.0 Q, and 1.05 Q conditions were analyzed (Q is the mass flow), the changes in gas volume fraction in the impeller channel were captured, the distribution characteristics of cavitation under different NPSH values were explored, and the change law of cavitation with time was determined. The results show that, when NPSH dropped to 95 m, the impeller cavitation first occurred under the 1.05 Q operating condition, and the impeller cavitation volume fraction was 0.0379525. When NPSH dropped to 85 m, the impeller cavitation occurred under the 1.0 Q operating condition, and the impeller cavitation volume fraction was 0.0185164. When NPSH dropped to 80 m, the impeller cavitation occurred under the condition of 0.95 Q, and the volume fraction of the impeller cavitation was 0.013541. The high-speed pump-jet propeller had better anti-cavitation ability with a small flow rate. The cavitation distribution law under the three operating conditions was similar; cavitation was first generated on the impeller inlet edge and near the shroud, and the vacuoles with large volumes were mostly concentrated on the impeller inlet side. As the NPSH gradually decreased, the entire flow channel was gradually occupied by vacuoles. As the flow decreased, the corresponding NPSH also decreased. When NPSH dropped to 50 m, the volume fraction of the impeller under all three operating conditions reached around 0.4. As the cavitation only occurred on the suction surface, the volume fraction of the cavitation on the suction surface exceeded 0.8, at which time the impeller had already undergone severe cavitation. Within a complete cycle, bubbles first appeared at the inlet edge of the impeller (measured near the shroud) and gradually spread toward the middle and rear of the impeller, ultimately covering the suction surface of the impeller. Under the design condition, the experimental results of the model pump were consistent with the numerical simulation results, and the error was only 2.68%, thus verifying the reliability of the numerical simulation. The research results provide a reference for the in-depth study of the cavitation performance of high-speed pump-jet propellers and provide a good theoretical basis and practical significance in the engineering field for the high-speed and miniaturization process of high-speed pump-jet propellers.

show abstract

Section: Boundary Conditionsmentioning

confidence: 99%

The Transient Characteristics of the Cavitation Evolution of the Shroud of High-Speed Pump-Jet Propellers under Different Operating Conditions

Gan,

Shi,

et al. 2023

Water

View full text Add to dashboard Cite

show abstract

“…During the startup process, the flow is highly unstable and there is a significant instantaneous surge in head when the speed reaches the rated speed, and the impeller passage is filled with backflow and vortices. In 2020, Han et al [13] proposed a method based on a combination of water tank experiment and numerical simulation to study the transient characteristics of a helical mixed flow pump during startup. The results show that the hydraulic performance parameters of the test pump, such as flow rate, head and shaft power, all initially increase and then gradually decrease to reach a relatively stable state.…”

Section: Introductionmentioning

confidence: 99%

Transient Hydraulic Performance of a Prototype Pump during Starting and Stopping Periods

Zheng,

Ye,

Zhao

et al. 2023

Processes

View full text Add to dashboard Cite

In order to meet different operational requirements, existing low specific speed centrifugal pumps may have to be run at high speeds. Therefore, it is crucial to understand the transient performance of such centrifugal pumps during high speed starting and stopping. However, there are currently no experiments on the starting and stopping of low specific speed centrifugal pumps. In this paper, transient hydraulic performance experiments during starting and stopping had been carried out on an atypical open impeller centrifugal pump with a rated flow rate of 6 m3/h using an updated test rig. The correlation of speed, flow, head and shaft power with time was obtained for four flow ratios of 0.353, 1.022, 1.654 and 2.343 operating conditions. It was found that the fluctuation of the shaft power curve was the strongest during the starting process, and there was a significant impact phenomenon. The corresponding impact shaft power from small to large flow rates were 0.167 kW, 0.409 kW, 0.234 kW and 0.215 kW, and the shaft power impact phenomenon was the most obvious under rated operating conditions. During the stopping process, the speed, flow rate and head all remain stable for a small period of time, and the time required to decrease to 0 is longer than the time required to reach a stable state during starting. During stopping, the shaft power will instantly decrease, accompanied by varying degrees of fluctuations.

show abstract

“…This conclusion was made by comparing the internal flow state and pressure distribution of different acceleration schemes. Wei Han [29] et al conducted a study that utilized a combination of CFD numerical simulation and flume experiment. They achieved impeller speed control through the use of a user-defined function (UDF) and employed frequency control technology to investigate transient hydrodynamic coefficients during the start-up process of a water-jet propulsion with a screw-mixed pump.…”

Section: Introductionmentioning

confidence: 99%

Transient Hydrodynamic Characteristics of a High-Speed Axial Flow Water-Jet Pump during Variable Speed Process

Zhu,

Shi,

Gan

et al. 2023

JMSE

View full text Add to dashboard Cite

To investigate the transient characteristics of high-speed axial flow water-jet pumps during start-up and emergency acceleration as well as to analyze how different accelerations affect the performance of internal flow, the k–ω turbulence model of the SST model and Zwart cavitation model were used to perform unsteady simulation on an impeller rotating at a speed of 1850. The steady-state numerical simulation method was verified by the experimental data, the numerical calculation results were basically consistent with the experimental data, the margin of error was within 5%, and the numerical simulation method was reliable. The results show that there was an obvious transient effect in the process of variable speed, and the thrust reached a stable state later than the speed. The buffer times for start-up times of 1 s, 2 s, and 3 s were 0.0394 s, 0.0375 s, and 0.0282 s, respectively, and the buffer times for the acceleration times of 0.5 s, 1.0 s, and 1.5 s were 0.0330 s, 0.0273 s, and 0.0230 s, respectively. The greater the acceleration, the more serious the flow rate and thrust lag behind the speed, and the greater the impact thrust. Under the same acceleration, the buffer time required in the start-up process was 19.3~22.6% longer than that in the acceleration process. During the change in speed of the high-speed water-jet pump, the vortex core area of the suction surface (SS) first appeared on the side of the shroud at the inlet, increased with the increase in the rotational speed, and developed toward the middle of the impeller. However, after the flow was stabilized, the vortex core region gradually shrank and eventually disappeared. When the rotational speed reached 0.6 times the design speed, cavitation occurred at the leading edge (LE) of the blade, and the cavitation area increased with the increase in the rotational speed. When reaching the same speed, the greater the acceleration, the more serious the cavitation. Under the design speed, that is, 6000 r/min, the cavitation volume fraction of the 1 s start-up process was 7.32%, the 2 s start-up process was 5.84%, the 3 s start-up process was 5.32%, and the 0.5 s acceleration process was 6.86%. The cavitation volume fraction of the 1 s acceleration process was 5.04%, and that of the 1.5 s acceleration process was 4.23%. Under the same acceleration, the cavitation volume fraction of the start-up process was 6.7~25% larger than that of the acceleration process. Compared with the start-up process and acceleration process under the same acceleration, the accelerated process had a smaller region of vortex core, stronger anti-cavitation ability, and more stable flow than the start-up process. During the actual operation process of the water-jet pump, it is advisable to use smaller accelerations and segmented accelerations as much as possible until the design speed is reached. The research findings serve as a foundation for future investigations into the transient characteristics of high-speed water-jet pumps operating under variable speed conditions.

show abstract

Transient Characteristics of Water-Jet Propulsion with a Screw Mixed Pump during the Startup Process

Cited by 6 publications

References 18 publications

The Transient Characteristics of the Cavitation Evolution of the Shroud of High-Speed Pump-Jet Propellers under Different Operating Conditions

The Transient Characteristics of the Cavitation Evolution of the Shroud of High-Speed Pump-Jet Propellers under Different Operating Conditions

Transient Hydraulic Performance of a Prototype Pump during Starting and Stopping Periods

Transient Hydrodynamic Characteristics of a High-Speed Axial Flow Water-Jet Pump during Variable Speed Process

Contact Info

Product

Resources

About