Internal Pressure Fluctuations Research Articles

Study of transient pressure and fluctuation characteristics in a centrifugal pump using the delayed detached-eddy simulation method

This study employed OpenFOAM, the delayed detached-eddy simulation (DDES) turbulence model, and structured grids to develop numerical models for three centrifugal pumps with twisted blades. The internal pressure field, velocity field, forces, and fluctuation characteristics of the centrifugal pumps are comprehensively analyzed under various operating conditions. The findings indicate that the pressure is relatively higher in the flow passages near the volute tongue and the outlet within the impeller. Regions of high relative velocity (slip velocity) are mainly found on the suction side of the blades, indicating that the design of the blade suction side affects the fluid outward slip performance. As the flow rate increases, the forces and force fluctuation amplitudes of each pump component also rise. Conversely, as the rotational speed increases, the force on the blades or impeller gradually increases while the fluctuation amplitude decreases. In the stationary domain, the force on the volute gradually decreases while the fluctuation amplitude of this force increases. The shape of the volute tongue influences the rate at which pressure inside the volute is converted to outlet pressure. The power spectral density (PSD) of pressure fluctuations is smallest at the nominal flow rate, displaying a clear and distinct axial frequency pattern without complex low-frequency fluctuations. Under low flow and high-speed conditions, the PSD at the axial frequency is relatively small, whereas the pressure PSD at other low frequencies is relatively large. This indicates instability in the flow under these conditions.

Failure analysis of atmospheric relief diaphragm in the low pressure steam turbine

In this study, the causes of failure and prevention methods for the atmospheric relief diaphragm in a low-pressure steam turbine were evaluated. The atmospheric relief diaphragm is designed to vent and burst at its center when the pressure in the exhaust housing exceeds 0.7 barG due to steam. However, visual inspection revealed that failure occurred along the flange mounting, rather than at the center of the diaphragm. Fatigue failure was identified as the cause, based on SEM analysis. Internal pressure fluctuations in the turbine caused bending along the fixed edge of the diaphragm. To confirm the occurrence of fatigue failure, finite element analysis was performed using a maximum internal pressure of 0.023 barG and a frequency of 60 Hz. The maximum deformation was 18.8 mm, which is less than the distance between the diaphragm and the knife, 30 mm. However, the maximum stress was 23.7 MPa, which exceeded the fatigue strength of A1050, 15 MPa, with stress concentration at the diaphragm edge, confirming edge fatigue failure prior to central knife failure. To identify an alternative material, finite element analysis was conducted using higher fatigue strength than A1050 under the same conditions. While the maximum stress was similar to that of A1050, it was below the fatigue strength of the alternative materials. Consequently, to prevent unexpected failures, it is recommended to use materials with higher fatigue strength than A1050 to enhance fatigue life of the diaphragm.

Numerical Study on Pressure Fluctuation in Electric Coolant Pump

Abstract Adjusting the flow rate of an electronic coolant pump (ECP) over a wide range can cause significant internal pressure fluctuations, leading to vibration and noise. This study uses numerical simulation to compare pressure fluctuations at the backflow orifice and within the impeller of an ECP at various flow rates. The backflow creates periodic disturbances in the impeller inlet region. As the flow rate increases, the axial influence range of the backflow on the impeller inlet decreases, reducing the amplitude of pressure fluctuations by up to 7.9%. The characteristic frequencies of pressure fluctuations at the backflow orifice include the blade passing frequency and its first harmonic. Within the impeller, the pressure fluctuation amplitude increases with both flow direction and flow rate, with characteristic frequencies encompassing the rotational frequency, BPF, and its first harmonic. At low flow rates, the overall variation of pressure fluctuations inside the impeller shows an opposite trend compared to design and high flow rates. The impact of the rotational frequency on pressure fluctuations inside the impeller is significantly smaller at the design flow rate than at other flow rates. This study offers insights that can help optimize ECP design and enhance their operational performance.

Research on Internal Flow and Pressure Fluctuation Characteristics of Centrifugal Pumps as Turbines with Different Blade Wrap Angles

The use of pumps as turbines has been gaining more and more attention in recent years. The present work mainly investigates the influence of blade wrap angle on the internal flow and pressure fluctuation characteristics of centrifugal pumps as turbines. Five different wrap angles (35°,45°, 55°, 65°, and 75°) for a forward-curved impeller were numerically analyzed under multiple operating conditions. The accuracy of numerical simulation was validated by experimental results. The results show that maximum efficiency is achieved with a blade wrap angle of 35°, and the highest efficiency flow point gradually decreases as the blade wrap angle increases. It is found by conducting entropy production theory analysis that the high-entropy production rate regions in PATs are concentrated in the volute tongue and impeller blade inlet regions, and that the entropy production rate at the impeller inlet region increases and then decreases as the blade wrap angle decreases. In addition, pressure pulsation was affected not only by dynamic and static interference but also by an irregular vortex around the impeller; its magnitude under Qt is higher than 0.8Qt for blade wrap angles of 55° and 75°. The primary frequency of pressure pulsation within the impeller is the axial frequency fn and its multiples, and the frequency with the largest amplitude is 3fn. The periodicity of vortices is closely related to the periodicity of pressure pulsation. And it is suggested that a PAT with a 35° blade wrap angle is advantageous for improving the stability of a turbine.

Exploration of shock–droplet interaction based on high-fidelity simulation and improved theoretical model

Shock–droplet interaction in the early stage involves intricate wave structures. Investigating this phenomenon is inherently challenging due to the fine spatial and temporal scales involved. Past research has suggested that the occurrence of cavitation, marked by a negative peak pressure, is linked to the focus of the reflected expansion wave. In this study, a high-fidelity compressible numerical approach is utilized to replicate the initial phase of shock–droplet interactions. The location of the negative peak pressure is meticulously documented and compared with experimental measurement and numerical results. Results indicate a strong alignment between the negative peak pressure positions identified through numerical simulations and the focal points identified in theoretical models for low gas–liquid wave velocity ratios. However, this alignment is notably disrupted when dealing with higher gas–liquid wave velocity ratios. Further enhancements are made to the theoretical model, enabling a more precise depiction of internal wave structures and focus points, particularly under conditions of high gas–liquid wave velocity ratios. The study delves into the various factors influencing internal pressure fluctuations within the liquid droplet, categorizing them into four phases: the shock wave effect, relaxation effect, fluctuation effect, and expansion wave effect. Analysing the pressure decrease portion reveals that while the converging of the reflected expansion wave leads to a substantial pressure drop, it accounts for only a fraction of the total pressure variation. Consequently, any model predicting negative peak pressure positions must comprehensively consider all contributing factors.

Experimental and numerical study of a fluidic oscillator frequency domain characteristics

Fluidic oscillators are fluid devices that provide steady flow at the inlet while generating unsteady flow at the outlet. This paper aims to investigate the frequency domain characteristics of internal pressure fluctuations in a specific type of fluidic oscillator to gain a deeper understanding of its dynamic behavior. The following conclusions were drawn: (1) Within a certain range, as the inlet-to-outlet pressure ratio increases, the oscillation frequency of the fluidic oscillator continuously rises, and the oscillation amplitude strengthens. (2) As the jet nozzle velocity increases within a certain range, the jet oscillation frequency exhibits a linear upward trend. These research findings provide essential academic and engineering guidance for designing and applying fluidic oscillators, assisting engineers in better understanding and controlling the device’s performance to meet the requirements of various application domains.

Study on characteristics of gas–liquid two-phase flow in pump as turbine using multiple-size group model

The multi-size group (MUSIG) model is employed in this paper to simulate the gas–liquid two-phase flow in pump as turbine (PAT) since the traditional Eulerian–Eulerian two-fluid model is unable to take into account the phenomena of breakup and coalescence of bubbles. First, the simulation of gas–liquid two-phase flow in a square column is compared with the experiment to verify the accuracy of the MUSIG model. Then, the results of gas–liquid two-phase flow in PAT simulated by the MUSIG model are compared with those by the conventional uniform bubble (UB) model and find that the MUSIG model is more favorable to capture the flow pattern at high gas content compared to the UB model. Based on the MUSIG model, the internal flow characteristics, pressure fluctuation, and bubble size distribution of the PAT are analyzed. The rotation of the blades breaks a part of big bubbles into small bubbles in the volute, resulting in a smaller diameter of the bubbles entering the impeller. As the gas content increases, the number and size of vortices in the impeller flow channel increase. The vortex is formed at locations where the gas phase distribution in the impeller flow channel is concentrated. The outlet of the impeller is more prone to bubble consolidation under high gas content conditions. In conclusion, the MUSIG model can well predict the complex flow characteristics of gas–liquid two-phase inside the PAT and identify the key influencing factors of energy acquisition, which can provide support for improving the performance of the PAT design.

A numerical analysis on the thermal characteristics by filling parameters of high-pressure valve for hydrogen refueling station

Renewable hydrogen plays a critical role in the current energy transition, and can facilitate the decarbonization and de-fossilization of hard-to-abate sectors, such as the industrial, power, transportation and buildings sectors. High pressure hydrogen valve（HPHV）is an important energy storage element for the hydrogen fueling station. Given the problems of large internal pressure fluctuation and long adjustment time of the HPHV during the operation of the current hydrogen fueling system, it is necessary to study the thermal effects of the HPHV. In the study，the pressure、temperature and velocity changes of the HPHV are studied from the aspect of numerical calculation. The hydrogen pressure and temperature changes of the model were simulated and analyzed at the different filling parameters. The accuracy of the simulation model was demonstrated by practice. The influence of the internal taper of the spool on the temperature change of 40°, 50°, 60° and 70° was studied. The influence of outlet pressure of 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa on the temperature of high-pressure hydrogen valve and the influence of mass flow rate of 0.1 g/s, 0.3 g/s, 0.5 g/s, 0.8 g/s on the velocity field of hydrogen high-pressure valve. The study shows that when the taper was 60°, the optimal decompression performance, small temperature rise, and the performance was stable. The highest speed and the lowest temperature appear near the gap outlet, up to 2500 m/s and 85 K, respectively. The temperature and speed change trends were basically opposite, and the temperature change range of the outlet was 280 K–370 K. The results of this study provide great support for the research and application of ultra-high pressure hydrogen storage and hydrogen refueling, which also provide a theoretical basis for the subsequent development of the hydrogen energy industry and the wide application of hydrogen fuel cell vehicles, and provide ideas for realizing the goal of “dual carbon".

Optimization of Magnetic Pump Impeller Based on Blade Load Curve and Internal Flow Study

Compared to traditional centrifugal pumps, magnetic pumps are widely used in industries such as chemical, pharmaceutical, and petroleum due to their characteristics of leakage-free operation and the ability to transport toxic and corrosive fluids. However, the efficiency of magnetic pumps is relatively low. Improving the efficiency of pumps helps to reduce energy loss and lower industrial costs. In this study, a magnetic pump was chosen as the research subject. The study aims to improve the efficiency and stability of the magnetic pump by optimizing the impeller blades based on the load curve. A combined approach of a numerical simulation and experimental verification was used to investigate the impact of the anterior loading point (AL), posterior loading point (PL), and slope (SL) in the blade loading curve on the pump’s performance. The slope, which had the most significant impact on pump performance, was selected as the dependent variable to analyze the internal pressure pulsation and main shaft radial force of the magnetic pump. The research found that the hydraulic performance test results of the magnetic pump were in good agreement with the simulation results. When efficiency is used as the optimization objective, the anterior loading point should be moved as far back as possible, and the posterior loading point should be moved as far forward as possible. Through the study of internal pressure fluctuations and radial forces within the pump, the radial force distribution is sequentially as follows: the anterior loading method, posterior loading method, and middle loading method at a rated flow rate. The maximum pressure pulsation amplitude was near the volute casing diffuser area. Compared to the original pump, the optimized magnetic pump showed a 5.05% improvement in hydraulic efficiency under the rated conditions. This research contributes to enhancing the performance and efficiency of magnetic pumps, making them more suitable for various industrial applications.

Effect of different draft tube designs on the phase resonance in a pump-turbine based on compressible CFD simulation

An investigation into projects with significant noise issues during full-load turbine operation revealed a distinct draft tube elbow design difference compared to more successful projects. This prompted an initiative to explore the impact of draft tube shape on pressure pulsations within the pump-turbine during full-load operation. Various draft tube designs were tested on the same prototype-scale pump-turbine unit using 3D compressible transient simulations. Results indicated increased pressure pulsation amplitude in the spiral casing for the flat elbow draft tube, accompanied by phase shifts that rendered pressure pulsations close to zero at certain locations, converting direct pulsations into indirect ones. Moreover, phase variations in the opposing runner channel aligned with multiples of the rotation period, suggesting possible cancellation of pressure pulsation waves. These improvements were confirmed through contour analysis, which showed reduced negative pressure areas in the draft tube, minimized pressure differences, and more uniform and stable streamlines. This study analyses the influence of draft tube shape on internal flow field pressure fluctuations, offering theoretical insights for enhancing pump turbine stability and guiding further research.

Evaluation and Investigation of Hydraulic Performance Characteristics in an Axial Pump Based on CFD and Acoustic Analysis

In this work, the internal flow behaviour and characteristic pressure fluctuations of an axial pump with varying water conditions are analysed. The impact of tip vortex flow on the pattern of turbulent flow is simulated numerically by the application of the CFD technique and experimentally using an acoustics analysis method. The numerical CFD data are verified with an experimental test model for accuracy and reliability. Based on the results, the difference in pressure in the internal flow and at the surfaces of the blade can be impacted through tip leakage vortex regions, which leads to changes in internal flow. Subsequently, the flow in the clearance and tip leakage vortex regions is changed. Moreover, the results reveal that the suction wall upstream is more unsteady near the surface due to more mixing, secondary flow, and tip leakage vortices. Pressure fluctuation occurs near the tip of the blade, caused by the increasing vortex flow velocity and hence raising the turbulent kinetic energy (TKE). Using different monitoring points at the blade impeller reveals high values of the pulsation amplitude. Owing to the region of clearance backflow under low-water conditions, the axial pump displays larger fluctuations in pressure near the tip blade area. Because the leakage flow leaves the gap at a high flow rate, shear layers are formed quickly between the main flow and the leakage flow. Near the end wall, there is a negative-vorticity-induced vortex. Moreover, as the flow rate increases, the pump’s amplitude decreases along with its main frequency. For the low-water flow, the results reveal that there is an important clearance backflow because the axial pump has large clearance.

Evaluating the effects of cavitating refrigerant flow on noise radiation from electronic expansion valve: a numerical study

The electronic expansion valve (EEV) is a critical component in air conditioners, responsible for regulating refrigerant flow rate and controlling the cooling or heating performance. However, it is also a significant source of noise. When the valve opening ratio is low, the increased flow velocity of the refrigerant can cause pressure to drop below the vapor pressure and result in a cavitation flow. This type of flow is known to produce higher levels of flow noise compared to single-phase liquid refrigerant flow. A Large Eddy Simulation is utilized to compute the internal flow of the EEV, incorporating a homogeneous mixture model to model cavitation phenomena. The structural vibration of the EEV and its inlet/outlet pipe wall is computed using high-resolution finite element methods with excitation force from internal wall pressure fluctuations. The near and far field noise radiation from the structure is calculated using finite and boundary element methods, respectively. The developed numerical methods are applied to two operating conditions: single-phase and two-phase. The results indicate that the noise radiation from the EEV is 6.5 dB higher in the cavitating flow than in the single liquid flow, closely matching the measured data. The current numerical methodology is expected to be useful in designing low-noise EEV units.

Simulation Analysis of Pipeline Detection Robot Motion State

Pipeline transportation has the advantages of safety, reliability and low energy consumption in transporting natural gas, and is an important transportation route for transporting natural gas. Due to the characteristics of natural gas pipelines with large internal pressure fluctuations, plenty of pipeline bending sections and complex pipeline deformation characteristics, pipeline detection robots are required to have higher detection capabilities, and the study of the motion state of natural gas pipeline detection robots in pipeline detection is of practical significance. This paper adopts the CFD numerical simulation method and establishes the model of DN800 pipeline deformation detection robot. Next, by simulating the natural gas pipeline detection robot under different media and different pipeline types respectively, the motion state of the detection robot is analyzed under different conditions. The simulation results verify the reliability of the detection robot working inside the pipeline, which can fully guarantee the safe transportation of natural gas pipeline.

Anomaly detection method for spacecraft propulsion system using frequency response functions of multiplexed FBG data

Anomaly detection and section estimation methods using multiplexed fiber Bragg gratings (FBGs) have been developed to identify propellant supply anomalies rapidly and autonomously in spacecraft propulsion systems. FBGs were used to measure the external strain of the pipe due to internal pressure fluctuations in the pipe during the pressure response caused by a water hammer. The measured strain was substituted into the constructed conversion formula to obtain the differential pressure through the FBGs. As a result, compared with the differential pressure measured by a conventional pressure sensor at the same position, the error was 2% for the maximum pressure of the water hammer and 1% for the natural frequency, indicating high applicability as a differential pressure sensor in piping with FBG simply wrapped around the outside of the pipe. Since the peak intensity and frequency of the measured values in the frequency domain change during flow anomaly and bubble localization, the frequency response function (FRF) between response data of the section to be detected was calculated, and the least-squares error of the FRF was used as the degree of anomaly. As a result, flow anomalies and bubble localization became detectable and sectional estimation was possible.

Clocking effect on the internal flow field and pressure fluctuation of PAT based on entropy production theory

The high-quality development of energy is closely related to the efficiency of energy utilization, and improving the hydraulic performance of the pump as turbine (PAT) has become increasingly important. To investigate the influence mechanism of the clocking effect on the hydraulic performance of the PAT, an energy loss analysis method based on entropy production theory is used to explore its hydraulic performance and internal flow characteristics. The results show that the clocking effect has an impact on the PAT at all flow rates. Compared to the initial scheme, the efficiency of the C6 scheme is improved by 1.60 % and 1.93 % at the 1.0QBEP and 1.43 QBEP conditions respectively. From C1 to C6, as the guide vane clocking angle increases, the flow field near the tongue and guide vane improves, and the loss of the vortices in the volute weakens, consequently improving the hydraulic performance of the PAT. The clocking effect's influence on pressure pulsation is more significant at low flow rates, with the C6 scheme exhibiting the best pressure pulsation characteristics. The research presented in this paper reveals the cause of the clocking effect and provides a theoretical basis for the hydraulic optimization of the PAT.

Energy loss and pressure fluctuation characteristics of coastal two-way channel pumping stations under the ultra-low head condition

The ultra-low head condition is a unique condition of the coastal two-way channel pumping stations, but the quantitative research on its hydraulic characteristics still needs to be improved. The entropy production method with computational fluid dynamics and the high-frequency pressure fluctuation test were employed to analyze the pumping device's internal energy loss and pressure fluctuation. The results show that the primary source of energy loss of the two-way channel pumping device under the ultra-low head condition is the turbulent dissipation caused by the velocity fluctuation of the impeller and guide vane, in which there are large irregular high entropy production areas on the pressure surface of the impeller and in the impeller channel. The high-frequency pressure fluctuation in the pumping device is mainly concentrated near the impeller, and the amplitude under the ultra-low head is 3.5 times the amplitude under the design head. Due to the dynamic and static interaction between the impeller and the guide vane, the frequency domain components of the pressure fluctuation at the outlet channel bell mouth are complex. Under the ultra-low head condition, the pressure fluctuation degree is intensified, the energy loss of each part is greater, and the low-frequency resonance should be prevented.

Circumferential groove on flow field and pressure fluctuation intensity of a semi-open centrifugal pump under design condition

The tip leakage flow (TLF) generated by the tip clearance has adverse effect on the performance of the impeller and increases pressure fluctuation. To suppress the effect of TLF on the instable flow in a semi-open centrifugal pump, the circumferential groove method is proposed in this paper. The effect of the circumferential groove on the internal flow and pressure fluctuation under the design condition is studied by combining numerical simulation with experiment. The results show that the head and efficiency were reduced by 1.1% and 1.0%, respectively. However, the circumferential groove provided a circumferential channel for leading edge overflow. The fluid in the groove formed a jet near the low-pressure region, which can effectively disperse the low-energy fluid of the blade inlet. The initial position and trajectory of the tip leakage vortex (TLV) move downstream, which decreases the relative flow angle and low-velocity region. The flow field in the blade tip region was improved remarkably. The low-frequency pressure fluctuation in the pressure surface and tip clearance of the blade inlet was suppressed by the circumferential groove, and pressure pulsation intensity decreased by 50% and 66%, respectively.

The Effects of Meridian Surface Shape on the Pressure Pulsation of a Multi-Stage Electric Submersible Pump

The influence mechanism of the internal pressure fluctuation propagation law of multi-stage submersible electric pump (ESP) is still unclear, which has been a major problem restricting the stable exploitation of deep-sea oil and gas. In order to investigate the effect of different meridian profiles on the pressure pulsation characteristics of three-stage submersible electric pumps, the unsteady Reynolds-averaged Navier–Stokes (URANS) method is used to numerically investigate it. The results show that the lower the pressure pulsation amplitude in the pump caused by the meridional shape that is more in line with the flow law, has a positive effect on the operation stability. The change of the shape of the meridian greatly affects the pressure pulsation law in the secondary and final pumps. The rotor–stator interaction causes the pressure pulsation amplitude of the monitoring point in the middle of the pump chamber to reach a peak value. By using continuous wavelet transform analysis, it is found that the regularity of 1–2 times frequency conversion is complicated due to multiple pulsation sources and low frequency propagation coupling between stages. At 3–6 times frequency, it is basically close to the pulsation rule of the blade frequency. The above research provides a basis for improving the operation stability of the ESP.

Experimental Study on the Effect of Inclination Angle on the Heat Transfer Characteristics of Pulsating Heat Pipe under Variable Heat Flux

This paper aims to deeply explore the influence of different inclination conditions on the heat transfer characteristics and broaden the application scene of a pulsating heat pipe. A test device for the heat transfer performance of a pulsating heat pipe under different inclination angles is designed and built. Under the condition of 70% liquid filling rate, ethanol and HFE-7100 are selected to carry out the experimental test with heating power of 40–140 W and dimensionless thermal difference of 0–0.56. The heat transfer performance, the temperature in the evaporation section and the internal pressure fluctuation of the pulsating heat pipe were experimentally studied. The results show that under the condition of uniform heat flux, for ethanol working medium, when the pulsating heat pipe is heated at 40 W, the operating thermal resistance varies significantly with different installation angles. At this time, the operating thermal resistance of a pulsating heat pipe with installation angles of 45°, 70°, 90° and D90° is 1.38 °C/W, 1.60 °C/W, 1.73 °C/W and 2.07 °C/W, respectively. With the increase in installation angle, the operating thermal resistance also increases gradually, reaching the maximum at 90°. At low heating power, the effect of the installation angle on the ethanol working medium is significantly greater than that of HFE-7100 working medium. The HFE-7100 working medium showed lower operating thermal resistance at low heating power, but with the increase in heating power, the operating thermal resistance of the two working medium gradually approached a 70% filling rate. Under non-uniform heating conditions, when HFE-7100 is used as a working fluid, the operating thermal resistance of a pulsating heat pipe under different heating power was lower than that of the ethanol working medium. The operating thermal resistance is less affected by the installation angle, and the overall heat transfer performance is better. The phenomenon in which the ethanol working medium is obviously affected by the installation angle can be improved by non-uniform heating conditions. For ethanol working medium, when the dimensionless heat difference reaches 0.33 under the condition of a 45° installation angle, the average temperature fluctuation in the evaporation section appears gentle. At this installation angle, the internal working medium of the four elbow pulsating heat pipe devices used in this research more easily forms a cycle in the pipe than the 90° installation angle.

Characteristics of internal and external pressures and peak net pressures on a building envelope

Net pressures on roofs and walls of a building are dependent on the internal and external pressure fluctuations. The internal pressure is influenced by the sizes and locations of the openings in the building envelope. The peak net pressure (Cp∨,net) for cladding design on the roof and walls of a building will depend on the internal and external pressure fluctuations and their correlation.External and internal pressure fluctuations and their correlations measured on the roof and wall of a 1:200 scale model nominally permeable building and a building with a wall opening were used derive peak net pressures. The large external suction pressures and the small internal pressures in the permeable building are positively correlated whilst the large external suction pressures and the large positive internal pressures in the building with windward wall opening are negatively correlated. Widely available basic statistical properties of external and internal pressures (i.e. mean, standard deviation, and peak coefficients) and their correlations are applied with the fundamental theory of the covariance integration method (without the need for their time histories) to satisfactorily estimate the peak net design pressure to within 10% of the measured value.