Search

In order to find a proper method to study the flow and sound fields in an axial-flow check valve, the jetting noise at a nozzle is investigated with simulations and experiments. Based on optimization principle, the main channel of the valve body is numerically investigated and optimized twice. The results show that the resistance coefficient and the maximum noise of the valve are decreased by 0.37 and 23.8 dB, respectively, and the head and the tail of the valve plug are optimized when streamline design is employed on the main channel structure of the valve body.

A pump-as-turbine is a hydraulic machine that can operate as a pump and turbine at the same time. Pump-as-turbine happens to be the most appropriate method for meeting the world’s energy demands, particularly in rural and isolated areas of a country. Furthermore, the operating cost of microhydropower systems is lower compared to conventional hydrodynamic turbines, but it requires high initial investment. Pump-as-turbine has been applied in many engineering fields such as irrigation, sewage, reverse osmosis, water distribution systems, farms, small pump storage power house, and pressure dropping valves. However, pump-as-turbine operates inefficiently at part-load due to lack of flow control device. In addition, the pump generates high flow instabilities in pump-as-turbine mode due to the shift of the best efficiency point toward higher head and discharge. This study extensively discusses the flow mechanism, modifications, and flow instabilities in the pump-as-turbine mode operation. First, the mechanism of the pump-as-turbine can be described as drawing out mechanical energy from the flow in the reverse mode. Since the energy drawn mainly depends on the major hydraulic components of the pump (impeller and volute), many studies have been conducted on the impeller and volute. It can be concluded that high amount of hydraulic losses is generated in pump-as-turbine mode operation. This can partly be attributed to the fixed geometrical parameters such as the stationary volute. To increase the usage of pump-as-turbine, it is very crucial to predict their performance in advance before manufacturing, which requires the understanding of the flow behavior as a result of geometrical parameters. In order to improve the energy conversion and understand the flow behavior in the centrifugal pump functioning as pump-as-turbine, the key geometrical parameters should be carefully designed. The designs of the main geometrical parameters do affect not only the hydraulic performance of pump-as-turbine but also the operational instability. The operational instability of hydraulic machines mainly depends on the pressure and the velocity fluctuation intensity generated within the flow passage as a result of the impeller–volute interaction. The magnitudes of the instabilities have the tendency to cause noise, vibration, harshness, and cavitation which reduces the life span of the hydraulic machine. Moreover, appropriate selection of the pump and unavailability of pump data contribute to the challenges faced. Finally, this review proposes specific solutions in terms of geometrical modifications and improvement of the computational design methods to handle the hydraulic losses faced during the pump operation; thus, this study can serve as a point of reference for a pump-as-turbine performance optimization.

Axial-flow fan with advantages such as large air volume, high head pressure, and low noise is commonly used in the work of air-conditioner outdoor unit. In order to investigate the internal flow mechanism of the axial-flow fan with different trailing edge structures of impellers, four kinds of impellers were designed, and numerical simulation and experiment were deployed in this article. The pressure distribution on the blades surface and distribution of vorticity in impellers were obtained using numerical simulation. Distribution of blade loading and velocity at the circumference are discussed. The relationship between the wideband noise and the trailing edge was established based on the experiment results. The results show that after the optimization of the trailing edge structure, the distribution of vorticity near the trailing edge of the blade is more uniform, especially at the trailing edge of 80% of the chord length of the suction surface. From the blade height position of 70% to the impeller tip, the pressure on the surface rapidly increases due to the tip vortex and the vortex shedding on the blade edge occurred in the top region of impeller. The pressure fluctuation amplitude at the trailing edge structure of the tail-edge optimization structure is smaller. In the distribution of blade loading, the three tail-edge optimization structures have smaller pressure fluctuations and pressure differences at the trailing edge structure. It is extremely important to control the fluctuation amplitude at the trailing edge. The amplitude of low-frequency sound pressure level of optimizing the trailing edge structure decreases obviously in the range of 50–125 Hz, and the optimization structure of trailing edge has an obvious effect on low-frequency wideband noise.

The robust parameter estimation of unknown space objects is essential to the on-orbit servicing missions. Based on the adaptive filtering techniques along with the dual quaternions modeling methods for pose estimation, this article proposes a dual vector quaternions–based extended Kalman filter and a dual vector quaternions–based adaptive fading factors extended Kalman filter to estimate the parameters of a free-floating tumbling space target. Using the dual vector quaternions to model the kinematics and dynamics of the system, the representation of the model is concise and compact. Also, the translational and rotational coupled effects are considered. In addition, the estimation algorithm is designed by the innovation-based multiple adaptive fading factors. As a result, the dual vector quaternions–based adaptive fading factors extended Kalman filter is robust against the faulty measurements which may lead to divergence of the traditional extended Kalman filter. As far as the authors know, both the designed filters are the first pose and inertial parameters estimation algorithms based on dual vector quaternions, and the dual vector quaternions–based adaptive fading factors extended Kalman filter is the first robust dual vector quaternions–based parameters estimating method. Finally, the proposed dual vector quaternions–based extended Kalman filter and dual vector quaternions–based adaptive fading factors extended Kalman filter are validated by mathematical simulations, and the dual vector quaternions–based adaptive fading factors extended Kalman filter is compared with the dual vector quaternions–based extended Kalman filter to show its robust performances.

Numerical calculations and experimental measurements were carried out in a closed hydraulic test rig to investigate the vibration characteristics and instabilities induced by the development of cavitation in a centrifugal pump. The internal flow characteristics in the impeller and vibration signals at four different positions of the pump system were analyzed during the cavitation process. The results revealed that the occurrence and development of cavitation could be effectively detected by the sudden increase in the intensity of vibration at the testing points. Corresponding relationships were formulated between the occurrence and the development of cavitation and the intensification of the vibration at the measuring locations. It was found out that the virtual incipient for cavitation was much smaller than the traditional “critical” point.

Vibration and dynamic stress caused by the interaction between the fluid and the structure can affect the reliability of pumps. This study presents an investigation of internal flow field and the structure response of residual heat removal pump using a combined calculation for turbulent flow, and the structure response of rotor was first defined using a two-way coupling method. For the calculation, the flow field is based on the shear stress transport k–ω turbulence model and the structure response is determined using an elastic structural dynamic equation. The results show that the domain frequencies of pressure fluctuations of monitors on the outlet of impeller are the integer multiples of rotating shaft frequency ( f n ) and the amplitude of the relatively large pressure fluctuation peak is the lowest under the design flow rate operating condition. Meanwhile, the time-average radial force value at the design flow rate condition is the smallest and the hydraulic force magnitude at the maximum operating flow rate condition is the largest, and phase difference can be clearly seen among the results obtained under different flow rates. Furthermore, the relatively large stress of rotor for all operating conditions is the biggest at shaft shoulder where the bearing is installed, and it increases with flow rate.

To reduce radial noises from the motor of centrifugal pumps, this study designed a water cooling system called jetting equipment to replace traditional fan cooling systems in pump motors. By measuring radiated noises, head, efficiency, and cavitation performance, the research compared the differences among experimental results of the original pump unit, the one with a normal design jetting pipe and another one with a larger jetting pipe. Results show that the radiated sound pressure level of the model pump was significantly reduced by 8.3 dB after integrating the jetting pipe. With a normal jetting pipe, no significant changes were observed in the head, efficiency, and shaft power curves, and cavitation performance improved under small flow rate. However, the performance with the larger jetting pipe worsened, except the hump phenomenon of the model pump under a small flow rate was enhanced. Computational fluid dynamics method was used to calculate the internal flow of three model pumps in order to investigate the jetting flow effect. A comparison among the flow fields at the inlet of the three types of pumps indicated that high-pressure water injection can effectively control inlet recirculation and improve velocity distribution in the inlet flow field with decreased recirculation vortex strength and recirculation onset critical flow rate.

Cavitation is a major undesirable phenomenon for centrifugal pump because it can cause hydraulic performance deterioration, pump damage by pitting and material erosion, and structural vibration and noise. Cavitation can appear within the entire range of the operating conditions; therefore, it must be prevented by all means. Sensorless monitoring technology based on motor current signature analysis is non-intrusive and economic for monitoring motor-driven equipment. Thus, this technology is suitable for centrifugal pump systems. The motor current signature for centrifugal pump load at the cavitation condition is the basis of this technology. However, systematic research is lacking on sensorless monitoring technology based on motor current signature. As a result, the tentative exploration for motor current signature at cavitation load was conducted in this study. The results show that the stator current is still a sinusoidal alternating current strictly to the law of sine. Moreover, the root mean square of the current fluctuates because of different flow regimes in the cavitation progress and decreases because vapor density is smaller than water density when cavitation is fully formed. For the stator current spectrum, the noise level, noise distribution, rotation speed, and vane pass frequency components show features in the cavitation process. These indicator indexes change according to the stage of cavitation development. Thus, the motor current signature analysis is found to be a feasible and cost-effective method for the stages of cavitation condition.

The hydraulic performances as well as the cavitation phenomena in a scaled residual heat removal pump were investigated by experimental and numerical methods, respectively. In particular, a 3D numerical model of cavitation was adopted to simulate the internal cavitating flow through the model pump. The hydraulic performances of the model pump predicted by numerical simulations were in good agreement with the corresponding experimental data. The main generation and evolution of attached cavitation throughout the blade channels at different cavitating conditions have been investigated using the vapor fraction ISO surface and in-plane velocity vectors. Results show that the low static pressure at the impeller inlet is the main reason for leading edge cavitation by correlation analysis of static pressure on the midspan of impeller. Cavitation proved to occur over a wide range of flow rates, producing a characteristic creeping shape of the head-drop curve and developing in the form of nonaxisymmetric cavities at design flow rate. Moreover, the occurrence of these cavities, attached to the suction surface of blades, was found to depend on the NPSHA value. Numerical and experimental results in this paper can provide better understanding of the origin of leading edge cavitation in residual heat removal pumps.

Centrifugal charging pumps are important components of nuclear power plants and must be operated under multioperating conditions for the requirements of the system. In order to investigate the internal flow mechanism of the centrifugal charging pump during the transient transition process of charging operating from Q = 34 m 3 /h to Q = 110 m 3 /h, numerical simulation and experiment are implemented in this study. The relationship between flow rate and time is obtained from the experiment and worked as the boundary condition to accurately accomplish the numerical simulation during the transient process. External and internal characteristics under the variable operating conditions are analyzed through the transient simulation. The results show that the liquid viscosity, large scale vortexes exist in the flow passages in the beginning of the variable operating conditions, which indicates flow separation and the sudden changes in direction of velocity. As the flow rate increases gradually, the flow angles of the fluid in inlet accelerate correspondingly and the flow along the blade is more uniform, which leads to a decrease and movements of the vortexes. The contents of the current work can provide references for the design optimization and fluid control of the pump used in the transient process of variable operating conditions.

This paper presents an investigation of pressure fluctuation of a single-suction volute-type centrifugal pump, particularly volute casing, by using numerical and experimental methods. A new type of hybrid Reynolds-averaged Navier-Stokes/Large Eddy Simulation, referred to as the shear stress transport-scale-adaptive simulation (SAS) model, is employed to study the unsteady flow. Statistical analysis method is adopted to show the pressure fluctuation intensity distribution in the volute channel. A test rig for pressure pulsation measurement is built to validate the numerical simulation results using eight transient pressure sensors in the middle section of the volute wall. Results show that the SAS model can accurately predict the inner flow field of centrifugal pumps. Radial force acting on the impeller presents a star distribution related to the blade number. Pressure fluctuation intensity is strongest near the tongue and shows irregular distribution in the pump casing. Pressure fluctuation is distributed symmetrically at the cross-section of the volute casing because the volute can eliminate the rotational movement of the liquid discharged from the impeller. Blade passing frequency and its multiples indicate the dominant frequency of the monitoring points within the volute, and the low-frequency pulsation, particularly in the shaft component, increases when it operates at off-design condition, particularly with a small flow rate. The reason is that the vortex wave is enhanced at the off-design condition, which has an effect on the axle and is presented in the shaft component in the frequency domain.

Flow-induced noise causes disturbances during the operation of centrifugal pumps and also affects their performance. The pumps often work at off-design conditions, mainly at part-load conditions, because of frequent changes in the pump device system. Consequently numerous unstable phenomena occur. In low specific speed centrifugal pumps the main disturbance is the inlet backflow, which is considered as one of the most important factors of flow-induced noise and vibration. In this study, a test rig of the flow-induced noise and vibration of the centrifugal pump was built to collect signals under various operating conditions. The three-dimensional unsteady flow of centrifugal pumps was calculated based on the Reynolds-averaged equations that resemble the shear stress transport (SST) k -ω turbulence model. The results show that the blade passing frequency and shaft frequency are dominant in the spectrum of flow-induced noise, whereas the shaft component, amplitude value at shaft frequency, and peak frequencies around the shaft increase with decreasing flow. Through flow field analysis, the inlet backflow of the impeller occurs under 0.7 times the design flow. The pressure pulsation spectrum with backflow conditions validates the flow-induced noise findings. The velocity characteristics of the backflow zone at the inlet pipe were analyzed, and the dynamic characteristics of the backflow eddy during one impeller rotating period were simultaneously obtained by employing the backflow conditions. A flow visualization experiment was performed to confirm the numerical calculations.