Pressure Pulsation Characteristics Research Articles

Tail cavity pressure pulsation characteristics under varying ventilation pressure and duration

Tail cavity pressure pulsation characteristics under varying ventilation pressure and duration

Numerical Simulation and Model Test on Pressure Fluctuation and Structural Characteristics of Lightweight Axial Flow Pump

In order to explore the relationship between the hydraulic performance, pressure pulsation, and structural characteristics of lightweight axial flow pumps, this paper takes the axial flow pump as the research object and analyzes pressure pulsation and structural characteristics by changing the blade length and thickness to realize the lightweight design of the axial flow pump impeller. Compared with the initial scheme (Scheme 1), the mass of the impeller is reduced by 17.2% (Scheme 2) and 29.9% (Scheme 3), respectively. The lightweight axial flow pump (Scheme 2 and Scheme 3) has a lower pressure pulsation amplitude at the impeller outlet monitoring point under large flow conditions. After the lightweight design of the axial flow pump impeller, the blade becomes shorter, the mass becomes lighter, and the cavitation performance will become worse. The maximum equivalent stress of Scheme 2 and Scheme 3 is increased by 2.8% and 31.9%, respectively, compared to Scheme 1. The maximum deformation of Scheme 3 increased by 27% compared to Scheme 1. This research can provide guidance for the lightweight optimization design of the axial flow pump.

Evolution mechanism of internal flow in the hump region and hump optimization of axial-flow reactor coolant pump

The Nuclear Reactor Coolant Pump (RCP) serves as a pivotal equipment in nuclear power plants, and its operational reliability is directly linked to the overall safety of the plant. When operating in the hump region, axial-flow reactor coolant pumps inevitably experience significant vibration and noise. Therefore, it is necessary to study the internal flow characteristics in the hump region to achieve effective control and increase the hump margin, keeping it away from the normal operating region. This study conducted analyses of pressure pulsation characteristics under various flow rates through experimentation. Additionally, numerical simulations were employed to scrutinize the internal flow of the pump under corresponding flow rates. Research has found that the disturbance of intermediate frequency signals is the main reason for the increase in pressure fluctuations in the hump region, rooted in the annular flow at the impeller inlet and vortex phenomena in the flow channel. Subsequently, the performance of the hump region was improved by optimizing the design of the vane inlet attack angle. The conclusions drawn from this study provide insights and a foundation for the optimal design of reactor coolant pumps.

Shock Wave and Aeroelastic Coupling in Overexpanded Nozzle

The growing demand for increasing the engine power of a liquid rocket is driving the development of high-power De-Laval nozzles, which is primarily achieved by increasing the expansion ratio. A high-expansion-ratio for De-Laval nozzles can cause flow separation, resulting in unsteady, asymmetric forces that can limit nozzle life. To enhance nozzle performance, various separation control methods have been proposed, but no methods have been fully implemented thus far due to the uncertainties associated with simulating flow phenomena. A numerical study of a high-area-ratio rocket engine is performed to analyze the aeroelastic performance of its structure under flow separation conditions. Based on numerical methodology, the flow inside a rocket nozzle (the VOLVO S1) is analyzed, and different separation patterns are comprehensively discussed, including both free shock separation (FSS) and restricted shock separation (RSS). Since the location of the flow separation point strongly depends on the turbulence model, both the single transport equation and two-transport-equation turbulence models are simulated, and the findings are compared with the experimental results. Therefore, the Spalart–Allmaras (SA) turbulence model is the ideal choice for this rocket nozzle geometry. A wavelet is used to analyze the amplitude frequencies from 0 to 100 Hz under various pressure fluctuation conditions. Based on a clear understanding of the flow field, an aeroelastic coupling method is carried out with loosely coupled computational fluid dynamics (CFD)/computational structural dynamics (CSD). Some insights into the aeroelasticity of the nozzle under separated flow conditions are obtained. The simulation results show the significant impact of the structural response on the inherent pressure pulsation characteristics resulting from flow separation.

Experimental study on energy and hydraulic performance of the axial flow pumping device with bell-shaped inlet channel

Abstract Due to the unique inlet design of the axial flow pump device with a bell shaped inlet channel, there is currently insufficient quantitative research on its hydraulic characteristics. This study investigates the hydraulic behavior of a vertical axial flow pumping device equipped with a bell-shaped inlet channel, analyzing various blade angles. Energy, cavitation, runaway, and pressure pulsation characteristics were assessed through meticulous testing on a high-precision test bench. Experimental findings indicate that altering the blade angle of the vertical axial flow pumping device with a bell-shaped inlet channel can influence its overall efficiency to some extent. Moreover, as the pump’s blade angle increases incrementally, the device’s cavitation performance gradually diminishes. Pressure pulsation tests reveal a relatively minor amplitude of pressure pulsation at the impeller outlet, contrasting with a more pronounced amplitude observed at the guide vane outlet compared to the pump outlet. These research results provide valuable insights for the design and optimization of actual pumping stations.

Pressure pulsation and radial force characteristics of dual-side impellers for the turbine energy recovery integrated machine

Abstract The inherent instabilities within the structure of the turbine-type energy recovery integrated machine (TT-ERIM) have the potential to compromise its smoothness and longevity, which could result in malfunctions. The dynamics of the dual-side impeller of TT-ERIM have been investigated through the use of computational fluid dynamics software (CFX) and the manipulation of the inlet flow rate. Pressure pulsation and radial force on each side under different flow conditions, and their impact on the hydraulic performance of the impeller and volute, are compared and evaluated through unsteady numerical calculations. The results show that the pressure fluctuation pattern of a centrifugal pump impeller is suboptimal at low flow rates, with fluctuations increasing as the flow rate falls below the rated value. Conversely, the pressure fluctuations of the turbine impeller remain consistent and are slightly reduced with excessively high flow rates. The generation of a negative pressure zone in the turbine impeller is indicative of an uneven overall pressure distribution. This research provides a theoretical framework for enhancing the TT-ERIM operational stability.

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.

Study on the internal flow evolution mechanism and pressure pulsation characteristics of the transient process of variable speed regulation of centrifugal pump

Abstract In view of the fact that it is not possible to quantitatively analyze any change in the internal flow characteristics of traditional centrifugal pumps during variable speed regulation, numerical computational fluid dynamics (CFD) simulations were carried out in this study to obtain the optimal adjustment range of variable speed regulation. A single-stage IS80-65-160 centrifugal pump is modeled in 3D using Pro/E and ICEM software, followed by CFD simulations. Results are compared with experimental data, showing good agreement. Variable speed adjustments ranging from 0.5-1.0 times the original values are applied to observe changes in internal flow characteristics, such as velocity and turbulent kinetic energy. Pressure and velocity variations in different parts of the pump are studied under varied working conditions. Pressure pulsation frequency domain characteristics are measured at monitoring points in the volute. Findings indicate that as flow rate decreases due to variable speed regulation, velocity decreases linearly, while turbulent kinetic energy decreases quadratically in a uniform distribution. Pressure fluctuations within the volute remain within 0.01 Cp range, but at the tongue, fluctuations can reach up to 0.6 Cp, suggesting an optimal adjustment range within 30% of the rated value.

Pressure Fluctuation Characteristics of a Pump-Turbine in the Hump Area under Different Flow Conditions

During the operation of a reversible pump-turbine, a hump area can easily appear under the pump condition, which will greatly affect the performance of a storage unit, with pressure pulsation being the key factor for the stable operation of a pump-turbine. Therefore, in order to explore the pressure pulsation characteristics of each flow component in the hump area, this paper first compared the full characteristics of the model test under different working conditions, and then it analyzed the pressure pulsation characteristics. By analyzing the pressure pulsation characteristics in the unit’s flow component under different flow rates in the hump area, the pulsation rule of a pump-turbine running in the hump area was revealed. It was found that the peak-to-peak value of the draft tube in the hump area was the smallest under the optimal flow condition, and the peak-to-peak value increased along the flow direction, with the rotor and stator interaction (RSI) effects being continuously enhanced. When away from the runner basin, the influence of RSI gradually weakened after leaving the runner. No low frequency was found in the optimal traffic. The peak-to-peak value of the low flow condition increased compared with the optimal flow condition, and the distribution was not uniform. The main frequency of the whole basin was relatively complex, indicating that the flow of water was unstable in the condition of partial load, resulting in the hump area during the unit operation. The research results can provide a theoretical reference for improving the stability of pump-turbines.

Analysis of the effect of cavitation on internal fluid excitation characteristics of centrifugal pumps

To explore the influence of cavitation on the internal fluid excitation characteristics of pumps, numerical simulations and performance testing evaluations were performed on the IS65-50-125 centrifugal pump. The prototype pump's exterior characteristic and cavitation performance curves, as well as its bubble volume distribution, were successfully replicated using numerical computations. The effect of cavitation on the internal pressure pulsation characteristics of the centrifugal pump under various operating situations was comprehensively investigated, indicating a relationship between the degree of cavitation and the root mean square values of pressure pulsation. Special emphasis was placed on the changes in features at intermediate and high frequencies, as well as the processes of rising bubble volume and vortex shedding at the impeller trailing edge on pressure pulsation. To validate the simulation results, a centrifugal pump vibration and noise testing platform was built, and studies on vibration intensity and internal sound field noise were conducted. The experimental results revealed that the vibration intensity and internal sound field sound pressure level of the centrifugal pump rose as cavitation conditions deteriorated, confirming the modeling results. This study's significant innovation is the precise identification of the pump's performance changes under different operating conditions by monitoring pressure pulsation changes at various frequencies, as well as an in-depth discussion of the impact mechanism of cavitation phenomena on the internal fluid excitation behavior of centrifugal pumps. The study demonstrates differences in pressure pulsation characteristics on the suction and pressure sides under various cavitation situations, as well as the process of vortex creation and shedding generated by bubbles in the impeller input channel during severe cavitation. This gives new theoretical basis for pump vibration and noise reduction, as well as significant improvements in centrifugal pump performance and stability.

Investigation on the pressure pulsation characteristics in a twin-screw multiphase pump

A three-dimensional gas–liquid two-phase transient numerical model for a twin-screw multiphase pump based on dynamic grid technology was established and validated with experiments. The pump's simulated pressure distributions, velocity fields, and pressure pulsations were analyzed to reveal the mechanisms of pressure transmission and pressure pulsation characteristics. The results indicated that the flow rate of the pump fluctuated twice due to the discharge of the male and female rotors in one cycle. As the inlet gas volume fractions increased, the flow rate decreased, but the pressure pulsations increased. At the engaging positions of the two rotor tips, a sudden pressure drop happened due to the combined effect of both tooth-tip and tooth-flank leakage. When the discharge port opened, the backflow happened; the flow rate and the pressure in the discharge chamber decreased, but the pressure in the working and suction chambers increased. When the suction port closed, a slight compression of the fluid in the low-pressure working chamber occurred, causing a pressure increase in the working chamber. The working chambers inhaled and discharged once in one cycle, so the first harmonic of pressure pulsations at the suction and discharge chamber was two times the running speed. The transient flow due to the simultaneous closing and opening of the suction and discharge ports at both sides of the male and female rotors generated a harmonic of four times the running speed. This study would help to improve the operational stability of twin-screw multiphase pumps.

Numerical Study of Low-Specific-Speed Centrifugal Pump Based on Principal Component Analysis

The characteristics of pressure pulsations in centrifugal pumps have attracted considerable attention. In this study, principal component analysis is used to discuss the pressure pulsations in a centrifugal pump with a low specific speed, and the primary causes for these pressure pulsations are analyzed in conjunction with experimental results. The results indicate that principal component analysis effectively separates the primary modes that influence the flow field characteristics. An excessive wrap angle results in the formation of a backflow vortex on the working face of the blade. Obvious stratification of the zero-order modal pressure indicates that the geometric structure of the impeller is rational and that the transient flow field is stable. The second- and third-order modes are conjugates, and their dominant frequency coincides with the dominant rotating frequency of the impeller, indicating that the pulsations of a single channel are the primary component of the pressure pulsations. The primary frequency (148.54 Hz) of the pressure pulsations at monitoring points distributed across the volute is three times the rotational frequency (49.51 Hz) of the impeller. The different positions and sub-frequencies of the monitoring points mean that the principal component analysis can effectively identify the impeller-induced sub-frequency difference.

Transient Flow-Induced Stress Investigation on a Prototype Reversible Pump–Turbine Runner

Pump–turbine units with high heads are subjected to strong pressure pulsations from the unsteady transient flow in fluid channels, which can produce severe vibrations and high stresses on the pump–turbine structural components. Therefore, reducing transient flow-induced stresses on prototype reversible pump–turbine units is an important measure for ensuring their safe and efficient operation. A high-head prototype reversible pump–turbine with a rated head of 440 m was used to investigate the transient flow characteristics and the flow-induced-stresses in this study. First, the flow passages of the pump–turbine unit and the structure of the reversible pump–turbine runner were constructed with CAD tools. Next, CFD simulations at the full load were performed to investigate the pressure pulsation characteristics of the pump turbine in both the time domain and the frequency domain. After this, the pressure files calculated by the CFD were exported and applied to a finite element model of the pump–turbine runner to calculate the transient flow-induced dynamic stresses. The results show that the pressure pulsations in the flow passage are closely related to the rotational speed, the guide vane number, and the runner blade number of the pump–turbine unit. The maximum flow-induced stresses on the pump–turbine runner at the full load were below 2 MPa and lower than the allowable value, which reveals that the designs of the pump–turbine runner and the flow passage are acceptable. The conclusions can be used as a reference to evaluate the design of high-head pump–turbines units. The approaches used to carry out the transient flow-induced stress calculations can be applied not only to pump–turbines units but also to other types of fluid turbomachinery such as pumps, turbines, fans, compressors, turbochargers, etc.

Study on partial load vortex and pressure pulsation characteristics of Francis turbine

Abstract Under partial load condition of the Francis turbine, problems such as hydraulic vibration, noise, and high amplitude pressure pulsation that endanger the safe and efficient operation of the unit are inevitable during the transient process. Based on dynamic grid technology and CFD technology, unsteady numerical simulation was conducted for the closing process of the active guide vane from 54% opening to 38% opening, and the evolution characteristics of internal vortex and pressure pulsation were analyzed. The results show that there is always a vortex structure at the crown of the runner during the transition process of variable load. Because of the vortex structure, a “banded” low-pressure zone appears on the suction surface of the blade, which gradually approaches the lower ring of the runner as the vortex structure develops. The analysis of the pressure signal in the runner region shows that the pressure coefficient on the suction surface fluctuates greatly due to the influence of the distribution position of the vortex structure, and the evolution of the vortex structure from continuous to local fracture will lead to a sudden increase of the pressure coefficient. In addition, the frequency components within the runner domain include the frequency of the movable guide vanes passing through the blade and the low-frequency components caused by the evolution of eddy currents within the runner.

Analysis of stability characteristics of pump-turbine in a pumped-storage power station with large head variation

Abstract The head variation is a key index of pumped storage power station, which is related to the operation stability of pump-turbine. The greater the head variation, the more difficult it is to ensure the operation stability of the unit. In this paper, the pressure pulsation of the pump-turbine with a large head variation is measured, and its amplitude and frequency characteristics are analysed. The prototype results are compared with the model test results. Similarities and differences of the pressure pulsation characteristics between the prototype and model are obtained. At the same time, the vibration characteristics of the prototype unit is measured, and the correlation analysis of the pressure fluctuation characteristics and the head variation is made. Then, the stability characteristics of pump turbines in the pumped storage power station are obtained. It guides the operation of the power station.

Numerical Investigation of Rotor and Stator Matching Mode on the Complex Flow Field and Pressure Pulsation of a Vaned Centrifugal Pump

The match of rotor and stator blades significantly affects the flow field structure and flow-induced pressure pulsation characteristics inside the pump. In order to study the effects of the rotor and stator matching mode on the complex flow field and pressure pulsation of a centrifugal pump with a vaned diffuser, this paper designs three different vaned diffusers (DY5, DY8 and DY9) and uses the DDES (Delayed Detached Eddy Simulation) numerical method combined with structured grids to simulate the unsteady flow phenomena of the model pump under rated conditions. The results show that, under different rotor and stator matching modes, the pressure pulsation spectrum is dominated by the blade passing frequency and its harmonics. The matching mode of the rotor and stator significantly affects the time–frequency domain characteristics of the pressure pulsation inside the pump, and it is observed that the pressure pulsation energy of vaned diffusers with more blades is significantly smaller than that of fewer-blade vaned diffusers in comparison to the energy of the pressure pulsation at the blade passing frequency and within the 10–1500 Hz frequency band. Combined with the distribution characteristics of the complex flow field inside the pump, it can be found that increasing the number of vaned diffuser blades can reduce the energy of flow-induced pressure pulsation, improve the distribution of high-energy vortices in the interaction zone and stabilize the flow inside the centrifugal pump effectively.

Research on pressure pulsation characteristics of a pump-turbine in pump mode with rotating stall: Focus on the broadband frequency

To investigate the adverse effects of rotating stalls on the pressure pulsation characteristics of a pump-turbine in pump mode, an unsteady numerical simulation was carried out by applying the partially averaged Navier–Stokes turbulence model. The numerical methods were carefully verified, and the onset flow rate of the hump at the performance curve and heads were in good agreement with the experimental data. The rotating stall appeared in the guide vane when the flow rate ranged from 0.514 to 0.887 times the best efficiency point (QBEP), with a frequency of 11.7% times the rotational frequency. In the period of a rotating stall, a sudden intensive pressure pulsation in the guide vane channel was observed and named as the component of the broadband frequency, and its corresponding flow mechanism was explained as the vortex evolution between the adjacent guide vane blades based on the dynamic mode decomposition technology. There were three distinct characteristics of broadband frequency: (i) intermittent occurrence when the rotating stall cell propagated to the current flow channel, (ii) a wide range of the frequency varying with flow rate, (iii) a considerable amplitude, e.g., reaching 21.1%–42.2% times that of the rotating stall frequency. In addition, both the frequency range and amplitude of the broadband frequency gradually decreased as the flow rate increased to 0.887QBEP. This study clarified the internal flow mechanism and frequency behaviors of a sudden intensive pressure pulsation if a rotating stall occurred, which was important to assess the stability of pump-turbine units.

Investigations of the Formation Mechanism and Pressure Pulsation Characteristics of Pipeline Gas-Liquid Slug Flows

The pipeline system is widely used in marine engineering, and the formation mechanism and flow patterns of two-phase slug flows are of great significance for the optimal design of and vibration prevention in a complex pipeline system. Aiming at the above problems, this paper proposes a modeling and solving method for gas-liquid slug flows. First, a VOF-PLIC-based coupling gas-liquid slug flow transport model is conducted. Second, to reduce the fuzzy boundary between the gas-liquid coupling interfaces, an artificial compression term is added to the transport equations, and the formation and evolution mechanism of severe slugging flow in piping systems is investigated. The pressure pulsation and gas content characteristics of the gas-liquid coupling process are explored. Research results found that the slugging phenomenon occurs at the gas-liquid interface, where liquid slugging frequency reaches its peak. The pipeline system has prominent periodic characteristics of the slugging phenomenon, and the period decreases when the gas-phase converted speed rises; pressure fluctuation amplitude increases, and the gas-phase velocity change is the inducing factor for the drastic change of pressure fluctuation. The research results can offer theoretical references for optimal designs of and vibration prevention in marine pipeline systems.

Effect of suction temperature on the internal flow characteristics of hydrogen circulation pump

This paper explores the effects of suction temperature (ST) on the internal flow and pressure pulsation characteristics of a roots hydrogen circulation pump (HCP). The study analyzes the suction and discharge chamber pressure pulsation, as well as the inlet and outlet flow pulsation, at different STs. The research finds that an increase in ST leads to a decrease in the amplitude and fluctuation intensity of the pressure pulsation in both suction and discharge chambers. Moreover, the average flow rate of the HCP decreases with increasing ST, while the frequency and waveform remain unchanged. The maximum and minimum values of the inlet flow pulsation decrease, while the maximum value of the outlet flow pulsation decreases, and the minimum value increases, indicating a reduction in fluctuation intensity. The turbulent energy within the discharge and transport chambers also changes with increasing ST. The inter-lobe leakage flow (ILF) is slightly affected by ST, while the radial leakage flow (RLF) and axial leakage flow (ALF) exhibit slight increases. Overall, these findings reveal the importance of considering ST as a critical design parameter for optimizing the performance and stability of the HCP.

Pressure Pulsation Characteristics on the Bulb Body of a Submersible Tubular Pump

Submersible tubular pumps are an ideal choice for pump stations that require high flow rates and low lift. These pumps combine the unique features of submersible motors with axial flow pump technology, making them highly efficient and cost-effective. They have found extensive applications in China’s rapidly developing water conservancy industry. In this research, we focus on investigating the pressure pulsation characteristics of the internal bulb body in a specific pump station project in China. To conduct our analysis, we utilize a model of the submersible tubular pump and strategically position 18 monitoring points. These monitoring points cover various sections, including the impeller inlet and outlet, guide vane outlet, as well as the inlet, middle, and outlet sections of the bulb body segment. To calculate the unsteady flow of the system, we employ numerical simulation techniques. By combining the outcomes of model tests, we determine the pressure pulsation characteristics. The comparison of results reveals a remarkable similarity between the efficiency–head curves obtained from the numerical simulation and the model test. While the model test yields slightly higher head results, the numerical simulation indicates slightly higher efficiency values. This finding lends strong support to the reliability of numerical simulation results, which can provide valuable insights for the design and optimization of submersible tubular pumps. Overall, submersible tubular pumps demonstrate their suitability for pump stations with high flow rates and low lift requirements. The study of pressure pulsation characteristics within the bulb body contributes to a better understanding of their performance and facilitates their further application in the field of water conservancy engineering.