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The present study emphasizes the experimental investigations of pressure fluctuations characteristics of the steady flow behavior in a low-head Francis turbine model operating under various load conditions. The experimental study was conducted on a scaled model of the Francis turbine with a runner diameter of 0.31847 m with a head of 17.66 m and operated at a speed of 950 rpm. The pressure fluctuations ranged their operating points from 70% during part load, 100% at the best efficiency point, to 110% under overload conditions. Pressure field measurements were conducted using miniature-type pressure sensors. Eight sensors were strategically placed at various locations, ranging from the spiral casing inlet to the draft tube. The outcomes facilitated identifying the sources of pressure fluctuations. Substantial pressure oscillation occurs on the model runner, vaneless space, and draft tube cone. The rotating vortex rope was formulated during the part load operation. The results show that the fundamental frequency of pressure fluctuations was 0.375 times the rotational runner frequency and strong pressure fluctuations were observed during part load operation. [ABSTRACT FROM AUTHOR]

A new measurement device, consisting of swirling blades and capsule-shaped throttling elements, is proposed in this study to eliminate typical measurement errors caused by complex flow patterns in gas-liquid flow. The swirling blades are used to transform the complex flow pattern into a forced annular flow. Drawing on the research of existing blockage flow meters and also exploiting the single-phase flow measurement theory, a formula is introduced to measure the phase-separated flow of gas and liquid. The formula requires the pressure ratio, Lockhart-Martinelli number (L-M number), and the gas phase Froude number. The unknown parameters appearing in the formula are fitted through numerical simulation using computational fluid dynamics (CFD), which involves a comprehensive analysis of the flow field inside the device from multiple perspectives, and takes into account the influence of pressure fluctuations. Finally, the measurement model is validated through an experimental error analysis. The results demonstrate that the measurement error can be maintained within ±8% for various flow patterns, including stratified flow, bubble flow, and wave flow. [ABSTRACT FROM AUTHOR]

In this article, considering the factors such as well trajectory and tubing string structures, the transient shut‐in tubing string pressure fluctuation model of ultra‐deep high‐temperature and high‐pressure (hereinafter referred to as HTHP) gas well is established, the propagation of pressure wave along the well depth is obtained, and the effects of different production and shut‐in time on the fluctuating pressure and its variation range are analyzed. Through calculation and analysis, it can be seen that there are differences in pressure waveforms at different well depths. The closer to the bottom of the well, the more delayed the occurrence of water hammer, and the smaller the water hammer pressure value. The larger the production, the greater the pressure wave velocity, and the closer to the wellhead, the more obvious the change. For well X, the pressure wave velocity in the well section below 6500 m varies greatly with the increase of production. When the production is 140 × 104 m3 D−1, the difference of pressure wave velocity between the bottom hole and the wellhead is 105.19 m s−1. After instantaneous shut‐in, the wellhead pressure increases by 3.2% compared with the initial pressure and the bottom hole pressure increases by 0.6%. [ABSTRACT FROM AUTHOR]

From an engineering point of view pulsatile pipe flows, which include the hydrodynamic and acoustic fluctuations, can cause many problems such as vibration, noise and structural fatigue etc. Knowledge of the characteristics of hydrodynamic fluctuations (pseudo sound) and acoustic waves inside pipes particularly those with bends make is crucial to pipeline vibration and noise reduction. Numerical simulation of the pulsatile pipe flows shows challenges especially in curved pipes with different flow modes compounded, and predicting the acoustic fluctuations is even tougher. In this work, the unsteady flows of a straight and curved pipe with a 90° elbow induced by a pulsatile pressure inlet were calculated by Detached Eddy Simulations (DES). The pipe acoustic fields are solved through an acoustic perturbation equation, which takes the time derivative of hydrodynamic pressure as the aeroacoustic source. The characteristics of the flow and sound fields are discussed detailly, and special attention is paid to the influence of the 90° elbow on the curved pipe flow. The results show that the amplitude of hydrodynamic pressure fluctuations decrease almost linearly along the straight pipe, and the 90° elbow has obvious local influence on the flow pressure and velocity especially in the downstream side. The acoustic field is of 1-D standing wave pattern because of the fundamental pulsation frequency lower than the pipe cutoff frequency, and the 90° elbow has only negligible effect on the acoustic field in the flow frequency range. [ABSTRACT FROM AUTHOR]

Pressure fluctuations in a mixing tank can provide valuable information about the existing flow regime within the tank, which in turn influences the degree of mixing that can be achieved. In the present work, we propose a prototype for identifying the flow regime in mechanically stirred tanks equipped with four vertical baffles through the characterization of pressure fluctuations. Our innovative proposal is based on force sensors strategically placed in the baffles of the mixing tank. The signals coming from the sensors are transmitted to an electronic module based on an Arduino UNO development board. In the electronic module, the pressure signals are conditioned, amplified and sent via Bluetooth to a computer. In the computer, the signals can be plotted or stored in an Excel file. In addition, the proposed system includes a moving average filtering and a hierarchical bottom-up clustering analysis that can determine the real-time flow regime (i.e., the Reynolds number, Re) in which the tank was operated during the mixing process. Finally, to demonstrate the versatility of the proposed prototype, experiments were conducted to identify the Reynolds number for different flow regimes (static, laminar, transition and turbulent), i.e., 0 ≤ R e ≤ 42,955. Obtained results were in agreement with the prevailing consensus on the onset and developed from different flow regimes in mechanically stirred tanks. [ABSTRACT FROM AUTHOR]

While repurposing the existing pipelines for hydrogen transport contribute to accelerated development of the full-scale hydrogen economy, the suitability of the aged pipelines should be assessed on their hydrogen embrittlement (HE) susceptibility in high-pressure gaseous hydrogen environments. In this work, a three-dimensional mechanics-hydrogen diffusion coupling finite element model was developed to determine the distribution of hydrogen (H) atoms at corrosion defect on pipelines under pressure fluctuations. Parametric effects, including corrosion defect dimensions (i.e., width, length, and depth) and pressure fluctuating parameters (i.e., cyclic load ratio and loading frequency), were determined. A high stress concentration exists in the longitudinal edge of the defect, while the stress level in the circumferential edge is low. The defect center is associated with the greatest stress and stress variation amplitude. H atoms tend to concentrate at the corrosion defect, especially the defect center, representing the most vulnerable site to initiate hydrogen-induced cracks. Most H atoms reside at the lattice sites, rather than the traps, indicating a limited capacity of the traps to host H atoms as compared to the crystalline lattice sites. With the increase in defect depth and length, both the stress level and stress variation amplitude at the corrosion defect are apparently elevated. More H atoms accumulate at the defect center, increasing the susceptibility to HE. As a comparison, the HE susceptibility of the corroded pipelines decreases with increased corrosion width. As the cyclic load ratio decreases, less H atoms accumulate at the corrosion defect. A decreasing cyclic loading frequency results in decreased stress variations but an increased H atom concentration at the corrosion center. The results provide a base to control pipeline HE by properly adjusting the operating pressure. • Develop a mechanics-hydrogen diffusion coupling model. • Model the hydrogen atom distribution at corrosion defect on aged pipelines repurposed for hydrogen transport. • Determine the effect of pressure fluctuations on hydrogen atom distribution. • Define the effect of corrosion defect dimension on hydrogen atom distribution. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a methodology for estimation of hydrodynamic loads acting on the bottom and at the walls of a stilling basin of a stepped chute with converging walls, based on the pressure measurements at the selected points of a scale model. This is the first study of hydrodynamic loads for this type of structure, and the first one of the loads on the stilling basin walls in general. For selected flow discharges, step heights and hydraulic jump submergence ratio, the hydrodynamic pressures were measured at a significant number of points, providing the spatio-temporal distribution of relevant hydrodynamic loads. The most influential effect proved to be a convergence angle of the chute walls. Based on these measurements, appropriate regression expressions were proposed for predicting hydrodynamic loads. These expressions show good agreement with measurements, offering a reliable tool for the structural design of stepped spillway stilling basins. [ABSTRACT FROM AUTHOR]

The wall pressure fluctuation fields on fairing surfaces and in the surrounding turbulent boundary layer are experimentally investigated. The fairings were in the shape of semi-ellipsoids and were mounted on the wall of a subsonic low-noise wind tunnel. Their heights amounted to 25% of the oncoming boundary layer thickness. The main physical features of the flows under consideration are determined by means of the surface oil-flow visualization. The fluctuating wall pressure field is compared with the flow pattern. It is shown that the greatest pressure fluctuation levels are recorded in the nose region of the fairing surface. It is established that lengthening the model leads to a considerable reduction of the pressure fluctuation strength in the region of flow separation from the fairing surface. [ABSTRACT FROM AUTHOR]

Pressure fluctuations caused by helical vortex rope in the draft tube is one of the main reasons for the instability of Francis turbines. Previous studies showed that drilling holes on runner cone can reduce the amplitude of pressure fluctuation. In this study, based on the runner cone which has been drilled one hole, two kinds of new runner cones are designed by means of drilling two more holes (2 holes runner cone) and drilling a slot (2 holes and 1 slot runner cone). Pressure fluctuation and flow pattern observation experiments as well as numerical simulations at partial load operation condition in a Francis turbine were carried out for the three types of runner cones. Analyses were performed to reveal the generation mechanism of the low frequency pressure fluctuations. The results showed that low frequency fluctuations are related to the cyclical rotation of helical vortex rope. Holes and slots on the runner cone have little impact on the efficiency of the Francis turbine. Slotting on the runner cone can reduce the amplitude of pressure fluctuation induced by vortex rope to a maximum of 29.41%. Hence, proper slotting on the runner cone can effectively reduce the low-frequency fluctuation caused by vortex rope in Francis turbines. These findings provide a new idea to improve the hydraulic instability of Francis turbines induced by vortex rope. [ABSTRACT FROM AUTHOR]

The accurate identification of the transition velocities Utrans in bubble columns (BCs) is important for their effective design, operation, and scale‐up. In this work, a novel parameter, namely, the new hybrid index (NHI), was developed and successfully applied to gas holdup and pressure fluctuations recorded in various BCs operated with water and aqueous solutions of alcohols (ethanol and propan‐2‐ol). The first Utrans was identified on the basis of a well‐pronounced local NHI minimum, whereas the second Utrans was distinguished by the point from which the NHI profile levels off. It was concluded that the main Utrans depend on the type of gas‐liquid system and sparger used. A set of several Utrans is reported. [ABSTRACT FROM AUTHOR]

The article discusses the existing methods of cooling reciprocating compressors, where special attention is paid to liquid systems in which the motion of the coolant is carried out not from an external pump, but due to fluctuations in gas pressure or rarefaction. An analysis of the designs of pumpless cooling systems is carried out, advantages and disadvantages are identified, directions for their further improvement are identified.

Pressure fluctuations in a mixing tank can provide valuable information about the existing flow regime within the tank, which in turn influences the degree of mixing that can be achieved. In the present work, we propose a prototype for identifying the flow regime in mechanically stirred tanks equipped with four vertical baffles through the characterization of pressure fluctuations. Our innovative proposal is based on force sensors strategically placed in the baffles of the mixing tank. The signals coming from the sensors are transmitted to an electronic module based on an Arduino UNO development board. In the electronic module, the pressure signals are conditioned, amplified and sent via Bluetooth to a computer. In the computer, the signals can be plotted or stored in an Excel file. In addition, the proposed system includes a moving average filtering and a hierarchical bottom-up clustering analysis that can determine the real-time flow regime (i.e., the Reynolds number, Re) in which the tank was operated during the mixing process. Finally, to demonstrate the versatility of the proposed prototype, experiments were conducted to identify the Reynolds number for different flow regimes (static, laminar, transition and turbulent), i.e., 0≤Re≤ 42,955. Obtained results were in agreement with the prevailing consensus on the onset and developed from different flow regimes in mechanically stirred tanks.

Representative elementary volumes (REVs) are an important concept in studying subsurface multiphase flow at the continuum scale. However, fluctuations in multiphase flow are currently not represented in continuum scale models, and their impact at the REV‐scale is unknown. Previous pore‐scale imaging studies on these fluctuations were limited to small samples with mm‐scale diameters and volumes on the order of ∼0.5 cm3. Here, we image steady‐state co‐injection experiments on a one‐inch diameter core plug sample, with nearly two orders of magnitude larger volume (21 cm3), while maintaining a pore‐scale resolution with X‐ray micro‐computed tomography. This was done for three total flow rates in a series of drainage fractional flow steps. Our observations differ markedly from those reported for mm‐scale samples in two ways: the macroscopic fluid distribution was less ramified at low capillary numbers (Ca) of 10−7; and the volume fraction of intermittency initially increased with increasing Ca (similar to mm‐scale observations), but then decreased at Ca of 10−7. Our results suggest that viscous forces may play a role in the cm‐scale fluid distribution, even at such low Ca, dampening intermittent pathway flow. A representative elementary volume study of the fluid saturation showed that this may be missed in smaller‐scale samples. Pressure drop measurements suggest that the observed pore‐scale fluctuations resulted in non‐Darcy like upscaled behavior. Overall, we show the usefulness of large field‐of‐view, high‐resolution imaging to bridge the gap between pore‐ and continuum‐scale multiphase flow studies. Key Points: The observations of fluctuations in multiphase flow on cm‐scale sample differ markedly from those reported for mm‐scale samplesViscous forces may play a role in the continuum‐scale fluid distribution even at low capillary numbersPore‐scale fluctuations can result in non‐Darcy like upscaled behavior [ABSTRACT FROM AUTHOR]

The results of in-flight experiments to determine the structure of the sound field in the cabin and pressure fluctuation fields on the surface of the fuselage of the RRJ-95NEW-100 prototype aircraft are presented here. Wall pressure fluctuation spectrums are obtained for three zones of measuring windows (forward, center, and rear fuselage) in cruising flight mode. The effect of the jet on the pressure fluctuation levels in the tail fuselage is considered. For an aircraft without an interior, the contribution of the main sources to the total intensity calculated through A-weighted overall sound pressure levels is determined. It has been determined that the main noise sources in the cabin of the RRJ-95NEW-100 prototype aircraft in cruising flight mode are pressure fluctuation fields on the fuselage surface (turbulent boundary layer noise) and the air conditioning system. The ratio between the sources varies along the length of the cabin. [ABSTRACT FROM AUTHOR]

The steady and unsteady characteristics of the internal flow in a high-speed centrifugal blower are studied by computational fluid dynamics (CFD) approach at low flow rates. It is demonstrated that as the flow rate decreases, the separation of flow in the blade passage becomes serious, and separated vortexes always occur on the suction surface of the blade which gradually expand and block the passage. The stall cells move downstream and generate vortices at the exit of the passage, resulting serious loss to the performance of the blower. Q-criteria is used to analyze the flow field and explore the evolution of the vortex structure in the impeller. It is further found that strong pressure fluctuations are caused by the rotating stall in the impeller. At the stall conditions, the instability characteristics are particularly obvious. At flow rates of 0.65Qn and 0.47Qn, the pressure fluctuation in the blade passage is dominated by the blade passing frequency, while a lower frequency dominates at 0.26Qn. Moreover, the flow on the suction surface of impeller blades fluctuates substantially. The characteristics of steady flow and unsteady flow can clearly explain the internal flow of centrifugal blower for vacuum cleaners at low-flow conditions, which can be widely used in various engineering designs of vacuum cleaners.

In the present work, the effects of modifying the tongue geometry of a centrifugal pump on pressure pulsations under the design and off-design conditions are carried out numerically by the unsteady analysis of fluid flow. Numerical modeling based on the Re-Normalization Group (RNG) k-ε turbulence model using a Mosaic mesh structure, a technology which can easily, quickly and formally connects any type of mesh for complex geometries and flow regimes, is applied to simulate the flow within the modeled pump, which is validated with the available experimental results. The flow is simulated through a commercial Computational Fluid Dynamics (CFD) software that solved Reynolds-Averaged Navier-Stokes (RANS) equations for a three-dimensional unsteady flow. In addition to choosing Qd (the design flow rate), 0.4 Qd and 1.2Qd are also taken into account as the inlet flow rates. Besides, pressures of 101KPa and 13KPa are considered as additional inlet conditions for this investigation. This unsteady simulation employing different inlet conditions is used to investigate the impacts of various volute tongue angles on the pressure coefficient (cp ). Results indicate that, overall, by changing the angle from 40° to 85°, the value of the pressure coefficient at the pump outlet grows by about 10% where it also causes a rise in the amplitude of pressure fluctuations. By the same token, a decrement to the inlet flow rate up to 40% of the nominal value brings about the amplitude of pressure fluctuations at the pump outlet to be increased significantly.

This paper numerically investigates the physical features of hydraulic jump oscillations at an abrupt drop with high Froude numbers reaching values up to 9.92. In order to emphasize the importance of the bottom shape, different relative step heights in the range between 0.9 and 3.4 have been analysed, leading to the occurrence of different jump regimes (A-wave, A-jump, B-wave and B-jump). For the case of the B-jump type, the jump toe is drifted downstream when the Froude number increases. For the A-jump type with high Froude, the surface roller is made up of an increasing several number of vortices and thus the jump toe is drifted upstream, when the Froude number increases. In particular, for the case of the A-jump type at the highest simulated Froude number, when the toe of the jump is at its most upstream location, the maximum number of anticlockwise vortices (with decreasing sizes) is observed. At the same time, the turbulence levels decrease much faster due to the dominance of viscous forces at the small scales. Instead, when the toe of the jump is moving downstream, the neighbouring vortices tend to influence each other with their rotation and to coalesce into one larger vortex and the turbulence levels increase rapidly due to the dominance of inertial forces. A statistical analysis indicates that turbulent pressure fluctuations increase rapidly from the toe of the jump and reach a peak in the roller region, downstream of which they decrease again. The structure of the turbulent pressure fluctuations depends on the Froude number. [ABSTRACT FROM AUTHOR]

This study uses measurements of pressure fluctuations of a full-scale ship for the calculation of the cavitation volume based on an acoustical model. The sound pressure signal had been recorded by pressure sensors mounted above the propeller of a 3600 TEU container vessel, combined with a synchronous tachometer signal from the propeller shaft. An acoustic monopole is used to model the unsteady sheet cavitation as a sound source. The analysis comprises intermediate high-pass filtering and integration followed by post-processing the resulting volume time signal. The cavitation volume evolution produced by consecutive blade passages shows well-recognisable steady growth and rapid collapse phases. By means of shape-dependend and time-synchronous sequencing and averaging methods, a representative volume signal of one blade passage has been deduced and several influential parameters have been identified. This allows modelling and manipulating the volume evolution and thus enables further investigations of the associated noise generation by propellers. [ABSTRACT FROM AUTHOR]

As crucial equipment in the industrial field, the stable operation of centrifugal pumps has drawn noteworthy attention. Relevant studies in the open literature have shown that intense pressure fluctuations have a major effect on the reliability and lifetime of centrifugal pumps. In the present paper, the pressure fluctuations in the centrifugal pumps are discussed in detail from different perspectives. The details of the studies are as follows. Firstly, the pressure fluctuation characteristics in centrifugal pumps are studied without considering clearance flow. Secondly, the pressure fluctuation property is investigated in detail for the pumps, with consideration for clearance flow. The pressure fluctuation characteristics in the wear ring, the pump-chamber clearance region, and the main stream region are studied, and the effect of clearance flow on the external performance of the pumps is analyzed. Thirdly, measures to reduce the pressure fluctuations and forces are summarized to improve the operational reliability of centrifugal pumps. Finally, conclusions and future research perspectives in the field of centrifugal pumps are presented. This review presents the research highlights and progress in the field of pressure fluctuations, which is beneficial to the stable operation of centrifugal pumps in engineering. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for estimation of hydrodynamic loads acting on the bottom and at the walls of a stilling basin of a stepped chute with converging walls, based on the pressure measurements at the selected points of a scale model. This is the first study of hydrodynamic loads for this type of structure, and the first one of the loads on the stilling basin walls in general. For selected flow discharges, step heights and hydraulic jump submergence ratio, the hydrodynamic pressures were measured at a significant number of points, providing the spatio-temporal distribution of relevant hydrodynamic loads. The most influential effect proved to be a convergence angle of the chute walls. Based on these measurements, appropriate regression expressions were proposed for predicting hydrodynamic loads. These expressions show good agreement with measurements, offering a reliable tool for the structural design of stepped spillway stilling basins.

The steady and unsteady characteristics of the internal flow in a high-speed centrifugal blower are studied by computational fluid dynamics (CFD) approach at low flow rates. It is demonstrated that as the flow rate decreases, the separation of flow in the blade passage becomes serious, and separated vortexes always occur on the suction surface of the blade which gradually expand and block the passage. The stall cells move downstream and generate vortices at the exit of the passage, resulting serious loss to the performance of the blower. Q-criteria is used to analyze the flow field and explore the evolution of the vortex structure in the impeller. It is further found that strong pressure fluctuations are caused by the rotating stall in the impeller. At the stall conditions, the instability characteristics are particularly obvious. At flow rates of 0.65Qn and 0.47Qn, the pressure fluctuation in the blade passage is dominated by the blade passing frequency, while a lower frequency dominates at 0.26Qn. Moreover, the flow on the suction surface of impeller blades fluctuates substantially. The characteristics of steady flow and unsteady flow can clearly explain the internal flow of centrifugal blower for vacuum cleaners at low-flow conditions, which can be widely used in various engineering designs of vacuum cleaners. [ABSTRACT FROM AUTHOR]

Stilling basins with sudden expansions are one of the energy dissipation structures. In the hydraulic jump, pressure fluctuations cause significant damages in stilling basins by cavity formation, erosion, and vibration. Roughness can also lead to changes of the behavior of stream lines and vortices. Despite the large number of works on the topic, the role of roughness in spatial hydraulic jumps is not yet fully understood. Present research aimed to study the influence of rough bed on pressure fluctuations of S-jump in abrupt expanding stilling basin. Experiments were conducted in a 0.8 m width and 12 m length flume. Channel expansions ratios were 0.33, 0.5, 0.67, and 1 within the range of Froude numbers, 2 to 9.5. The results showed that roughness decreases intensity of pressure fluctuations in an abrupt expansion stilling basin. Additionally, in sudden expanding sections, the energy loss increases, and the intensity of pressure fluctuations decrease due to the formation of lateral vortices. The reduction rate of maximum pressure fluctuation was 27%, 46%, and 58% for expansion ratio of 0.67, 0.5, and 0.33, respectively. The results revealed the clear dependence of these variables on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609 < X < 3.385, where X is dimensionless distance from the toe of the hydraulic jump, which makes it highly advisable to reinforce the bed of stilling basins in this range. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The effect of fluctuating pressures due to turbulence on the hydraulic jump causes significant damage to the relaxation pool. Moreover, the presence of roughness in the bed changes the behavior of flow lines and the formation of vortices during the jump. Therefore, the aim of this study was to determine the effect of the presence of roughness on hydrodynamic pressures in type S hydraulic jump in sudden divergence sections. For this purpose, experiments were performed in a relatively large channel with a width of 0.8 and a length of 12 m in the calm pool with divergence ratios of 0.33, 0.5, 0.67 and 1 in the range of Frued numbers between 2 to 9.5. Roughness elements with a height of 3 cm and specified distances were placed in the channel bed and downstream of the divergence section. In order to determine the effects of roughness on the level of hydrodynamic pressures, the experiments were performed in two separate stages, including a completely flat pool bed without the presence of roughness in the first stage (77 experiments) and with the presence of roughness in the pool floor in the second stage (81 experiments). The results showed that the presence of roughness in the bed reduces the intensity of pressure fluctuations in the relaxation pool. In addition, in sudden divergent sections, due to the formation of lateral vortices, the energy drop increases and the intensity of pressure fluctuations decreases. The maximum reduction rates of pressure fluctuations were estimated to be 27, 46 and 58% for the divergence ratios of 0.67, 0.5 and 0.33 in the rough bed, respectively.

Unsteady cavitating flows around the INSEAN E779A propeller were studied numerically with the propeller operating downstream in a non-uniform wake. The objective of this work is to predict the cavitating flow along the rotating blades and to establish the relationship between the cavitation evolution and the pressure fluctuations. The analysis used the k - ω shear stress transport (k - ω SST) turbulence model and the ZGB cavitation model. Results using various grids show the solve methods capabilities for a wide range of conditions. The numerical results compare well with experimental data for the transient cavitating flow predictions in a non-uniform wake. Although the predictions slightly underestimate the cloud cavity formation, the evolution of the sheet cavity, tip vortex cavity and side-entrant jets are well reproduced as the blade goes through the wake. Further analyses demonstrate that the side-entrant jet is the primary cause driving the cavity to detach from the blade surface. Finally, cavity volume evolution and the excited pressure data are analyzed to show that the pressure fluctuations are mainly driven by the accelerating cavity volume growth. • Turbulent cavitating flow around a propeller in a non-uniform wake is simulated. • Rotating cavitation dynamics around a propeller is demonstrated. • The relationship between the cavitation evolution and the pressure fluctuations is discussed. [ABSTRACT FROM AUTHOR]

In this study wind induced surface pressure fluctuations during operation of an open volumetric cavity receiver were investigated in wind tunnel experiments. Due to the process design of the open volumetric receiver, surface pressure fluctuations impact the receiver mass flow which is crucial for cooling the highly irradiated receiver. For this study a model of a solar tower was constructed under the concept of similitude which allows wind tunnel experiments at Reynolds numbers up to 13.17 × 106. Transient pressure measurements were conducted under 17 different flow directions to evaluate the impact of separation induced pressure fluctuations. The experimental design further allows a rotation of the model to evaluate the impact of changes in wind direction on the surface pressure at the receiver. For cases under a constant wind direction, a critical angle range could be identified in head on wind with a horizontal inclination of 45.0 to 78.8° relative to the central receiver axis. The results further show that surface pressure fluctuations are more sensitive to changes in wind direction as the amplitudes with maximum 20 Pa for a Reynolds number of 13.17 × 106 are about one order of magnitude higher compared to the cases with a constant flow direction. Furthermore, a frequency analysis shows the shielding effect of the cavity design for side-wind as no peaks in the pressure spectrum appear. For flow directions within the critical range of 45.0 to 78.8° a main vortex shedding frequency under constant Strouhal numbers of 0.25 to 0.50 can be observed. [ABSTRACT FROM AUTHOR]

In the present work, the effects of modifying the tongue geometry of a centrifugal pump on pressure pulsations under the design and off-design conditions are carried out numerically by the unsteady analysis of fluid flow. Numerical modeling based on the Re-Normalization Group (RNG) k-e turbulence model using a Mosaic mesh structure, a technology which can easily, quickly and formally connects any type of mesh for complex geometries and flow regimes, is applied to simulate the flow within the modeled pump, which is validated with the available experimental results. The flow is simulated through a commercial Computational Fluid Dynamics (CFD) software that solved Reynolds-Averaged Navier-Stokes (RANS) equations for a three-dimensional unsteady flow. In addition to choosing Qd (the design flow rate), 0.4Qd and 1.2Qd are also taken into account as the inlet flow rates. Besides, pressures of 101KPa and 13KPa are considered as additional inlet conditions for this investigation. This unsteady simulation employing different inlet conditions is used to investigate the impacts of various volute tongue angles on the pressure coefficient (cp). Results indicate that, overall, by changing the angle from 40° to 85°, the value of the pressure coefficient at the pump outlet grows by about 10% where it also causes a rise in the amplitude of pressure fluctuations. By the same token, a decrement to the inlet flow rate up to 40% of the nominal value brings about the amplitude of pressure fluctuations at the pump outlet to be increased significantly. [ABSTRACT FROM AUTHOR]

A description is given of the causes by which the transmission of vibration and airborne noise from equipment to the environment should be controlled. The paths of this transmission and applicable ways for its reduction by passive and active methods are examined. It has been demonstrated that pipelines, even vibration-isolated from the equipment by means of expansion joints, can transmit and even amplify vibration from the installation in a wide frequency range. It is noted that reducing the vibration of pipelines is important for effective vibration isolation of equipment in power and transport machine building, shipbuilding, and of oil and gas pipelines at pump stations. Effective control of the vibration and noise transmission to the environment has been shown to require a preliminary comprehensive analysis of the importance of all paths of their transmission. A description is given of a dedicated universal research test facility for a comprehensive study of the possibility and methods for reducing the transmission of vibration and airborne noise from operating equipment with a flow of working fluid through piping using passive and active methods. [ABSTRACT FROM AUTHOR]

The pressure signals were analyzed by time‐domain and frequency‐domain methods, including standard deviation, autocorrelation function, and power spectral density function, to investigate the bubble behavior and determine the regime transition. Results indicated that the autocorrelation function of pressure signals derived from bubbles was periodic fluctuation. The periodic nature of the autocorrelation function disappeared and the dominant frequency increased when the transition from bubbling to the turbulent regime occurred. The decrease of static bed height facilitated the explosion of bubbles, which accelerated the transition from the bubbling to the turbulent regime. The fluidization index was used as an indicator for the bubble state in the dense fluidized bed. [ABSTRACT FROM AUTHOR]

A voluminous liquid waste stream is generated as sodium nitrate (NaNO3) solution in Spent Nuclear Fuel Reprocessing Plants. Fluidized bed thermal denitration is a strong contender among various disposal options for this stream. In the present work experimental investigations on thermochemical denitration of NaNO3 have been carried out in an 80 NB laboratory scale fluidized bed reactor. Carbon based reductant was utilized to convert NaNO3 to sodium carbonate (Na2CO3) as well as to reduce denitration temperature. The operating parameters were optimized for maximum conversion of NaNO3 and 99.13% denitrification has been achieved. Pressure fluctuation across bed was also recorded and analysed in the state space domain employing attractor comparison technique. This technique computes a statistical metric ‘S’, as a measure of the fluidization state in the fluidized bed reactor and can be used for early detection of agglomeration in the bed. The sensitivity and early agglomeration detection capability of S-statistics are illustrated with experimental results for a liquid-sprayed gas fluidized bed.

The results of in-flight experiments to determine the structure of the sound field in the cabin and pressure fluctuation fields on the surface of the fuselage of the RRJ-95NEW-100 prototype aircraft are presented here. Wall pressure fluctuation spectrums are obtained for three zones of measuring windows (forward, center, and rear fuselage) in cruising flight mode. The effect of the jet on the pressure fluctuation levels in the tail fuselage is considered. For an aircraft without an interior, the contribution of the main sources to the total intensity calculated through A-weighted overall sound pressure levels is determined. It has been determined that the main noise sources in the cabin of the RRJ-95NEW-100 prototype aircraft in cruising flight mode are pressure fluctuation fields on the fuselage surface (turbulent boundary layer noise) and the air conditioning system. The ratio between the sources varies along the length of the cabin.

• Identification of acoustic and hydrodynamic properties of wall fluctuating pressure. • Flow field behavior characteristics of acoustic mode and hydrodynamic mode. • The contribution ratio of acoustic mode and hydrodynamic mode to spectral energy. In this study, an analysis method is proposed to explain the dynamic mode decomposition (DMD) mode of wall fluctuating pressure from the perspective of hydrodynamics and acoustics. According to the phase velocity, the wavenumber–frequency spectrum is divided into hydrodynamic, acoustic, and subconvective regions. Multiple DMD modes of the pressure field are calculated to obtain the wavenumber–frequency spectrum of the reconstructed pressure, which is characterized by the fact that the energy is concentrated at different wavenumber positions of the same frequency. This behavioral feature enables the DMD mode to be identified as a hydrodynamic, acoustic, and hybrid property according to the wavenumber position where the energy spot appears. This method can realize the classification and contribution analysis of the hydrodynamic and acoustic properties of the wall pressure DMD mode, and establish the mapping relationship between the acoustic mode and the eddy current characteristics through the eigenvalues. The coherent structure of the trace acoustic energy radiation in the incompressible fluid is observed from the statistical perspective, which increases understanding of the flow noise. The zero-pressure gradient wall flow experiment of Abraham is numerically analyzed using the aforementioned method. The results indicate that most of the DMD modes are identified as hydrodynamic, and only the nineteenth-order DMD mode is identified as acoustic. The frequency of the acoustic mode is 23.9 Hz, which has obvious wave-packet characteristics, whereas the hydrodynamic mode exhibits nonradiative convection characteristics, and its eddy current structure is closer to the wall transfer. [ABSTRACT FROM AUTHOR]

This study presents a new method for predicting the Critical Heat Flux (CHF) approaching condition in subcooled flow boiling based on pressure fluctuation analysis. Through experimental investigations, water flow in an upward direction was conducted within a mini-channel with one side heated to analyze the sequential boiling phenomena, including ONB (Onset of Nucleate Boiling), OFI (Onset of Flow Instability), and CHF. While ONB was determined using the slope of the wall temperature–heat flux, OFI was determined by considering the pressure drop through the channel and outlet pressure fluctuation. By analyzing the inlet pressure fluctuations, a new condition called "the CHF approaching condition" was introduced, which serves as a CHF precursor. The CHF approaching condition was found to be approximately 90% of the CHF value across all experimental scenarios. The proposed method provides an effective tool for predicting and preventing CHF, thereby reducing the potential risk of damage to the heating surface. [ABSTRACT FROM AUTHOR]

Pressure fluctuations in a gas-solid fluidized bed involve much information of the dynamic system. To uncover the value and significance of the pressure fluctuations time series, two meaningful tasks, i.e., the fluidization regime classification and the future state prediction, are investigated using Machine Learning (ML) algorithms, including Back Propagation neural network (BP), Convolutional Neural Network (CNN), Long Short-Term Memory network (LSTM), Radial Basis Function network (RBF), Random Forest (RF) and Support Vector Machine (SVM). Findings indicate that the six ML methods rank their performance for the classification task from high to low as: BP ∼ RF > SVM > CNN ∼ LSTM ∼ RBF. For the one-step-ahead future state prediction, the accuracy goes from high to low as: BP ∼ RBF > CNN ∼ LSTM > SVM ∼ RF, whilst for the multistep-ahead prediction the LSTM approach shows the best performance. Additionally, the sampling frequency of pressure time series has significant effects on both tasks. Overall, this study demonstrates the capability of machine learning methods for the value analysis of nonlinear time series and the better operation of gas-solid fluidization systems. [Display omitted] • Two meaningful tasks (classification and prediction) are studied by six ML methods. • pse , min , pp and rms are important features for flow regime classification by ML. • BP method shows best performance on one-step-ahead prediction of future state. • LSTM method shows best performance on multistep-ahead prediction of future state. [ABSTRACT FROM AUTHOR]

We report on the experimental study of a precessing vortex core (PVC) in an air model of a Francis turbine. The focus is placed on the modal decomposition of the PVC that occurs in the draft tube of the model turbine for a range of operation conditions. The turbulent flow fluctuations in the draft tube are assessed using stereo particle image velocimetry (PIV) measurements. Proper orthogonal decomposition (POD) is applied to the antisymmetric and symmetric components of the velocity fields to distinguish the dynamics of the azimuthal instabilities. The pressure pulsations induced by the PVC are measured by four pressure sensors mounted on the wall of the hydro turbine draft tube. Spatial Fourier decomposition is applied to the signals of the pressure sensors to identify the contributions of azimuthal modes, m = 1 and m = 2 , to the total pressure fluctuations. The analysis based on velocity and pressure data shows similar results regarding the identification of the PVC. The contribution of the m = 2 mode to the overall turbulent kinetic energy is significant for the part load regimes, where the flow rates are twice as low as at the best efficiency point (BEP). It is also shown that this mode is not the higher harmonic of the PVC, suggesting that it is driven by a different instability. Finally, we show a linear fit of the saturation amplitudes of the m = 1 and m = 2 oscillations to determine the critical bifurcation points of these modes. This yields critical swirl numbers of S c r = 0.47 and 0.61 , respectively. The fact that the PVC dynamics in hydro turbines are driven by two individual instabilities is relevant for the development of tailored active flow control of the PVC. [ABSTRACT FROM AUTHOR]

Visualization experiments and numerical simulations of two-phase flow are conducted to study the pressure fluctuation characteristics of oil-gas flow in horizontal pipes. The two-fluid model based on the Eulerian–Eulerian method is adopted, and the bubble number density equation (BNDE) is introduced to the simulation to predict the bubble size and distribution within the pipe. The bubble size and pressure variations in the pipe obtained from the simulations agree well with the recorded values from the experiments. The fast Fourier transform (FFT) algorithm is used to analyze the characteristics of pressure fluctuations, and the results show that the sudden pressure increase in the pipe sections is related to gas injection. The bubble number density increases with liquid flow rate (Ql), which causes the oil-gas flow to be more turbulent while increasing the amplitude of high-frequency fluctuations. The maximum amplitude for the dominant frequency is observed near the pump inlet for low liquid flow rates. At high liquid flow rates, more liquid vortices are found near the gas orifice, and there is a maximum amplitude for the dominant frequency in this section. Due to the high swirling strength at larger inlet gas volume fraction (IGVF), there is an obvious increase in the amplitude of low-frequency fluctuations, while the amplitude of high-frequency fluctuations is nearly the same under all IGVF. [ABSTRACT FROM AUTHOR]

Stilling basins with sudden expansions are one of the energy dissipation structures. In the hydraulic jump, pressure fluctuations cause significant damages in stilling basins by cavity formation, erosion, and vibration. Roughness can also lead to changes of the behavior of stream lines and vortices. Despite the large number of works on the topic, the role of roughness in spatial hydraulic jumps is not yet fully understood. Present research aimed to study the influence of rough bed on pressure fluctuations of S-jump in abrupt expanding stilling basin. Experiments were conducted in a 0.8 m width and 12 m length flume. Channel expansions ratios were 0.33, 0.5, 0.67, and 1 within the range of Froude numbers, 2 to 9.5. The results showed that roughness decreases intensity of pressure fluctuations in an abrupt expansion stilling basin. Additionally, in sudden expanding sections, the energy loss increases, and the intensity of pressure fluctuations decrease due to the formation of lateral vortices. The reduction rate of maximum pressure fluctuation was 27%, 46%, and 58% for expansion ratio of 0.67, 0.5, and 0.33, respectively. The results revealed the clear dependence of these variables on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609 < X < 3.385, where X is dimensionless distance from the toe of the hydraulic jump, which makes it highly advisable to reinforce the bed of stilling basins in this range.

The increase of liquid saturation badly affects the fluidization dynamics, even resulting in the failure of fluidization. Nevertheless, few researches focus on characterizing the flow pattern transition of wet particles. In this work, we discuss the effects of the liquid saturation, gas velocity and the particle size on the global fluidization dynamics of Geldart D particles by analyzing the pressure fluctuations in the fluidized bed. The results show that the bubble dynamics is intensified with the increasing liquid saturation and decreasing particle size. When the superficial gas velocity increases, the fluidization regimes change from expanding regime, to multi-bubbling regime and slugging. During the normal fluidization and slugging, the liquid bridge forces prevent the growth of large bubbles and promote the probability of bubble break-up. Thus, the average bubble size decreases and the number of bubbles increases, which lead to the intense bubble behavior. With the decreasing particle size, the effect of liquid bridge forces is enhanced, contributing to the intensified bubble dynamics, including fast rising, frequent coalescence and eruption of a large number of bubbles. Compared to dry particles, wet particles are easily to cause defluidization when the gas velocity is small. The PSD patterns have the sharp narrow peaks at frequency lower than 0.8 Hz. When the liquid saturation is increased to 30%, a gas channel forms in the bed, which resists the normal works of the fluidized bed. Basically, reducing the liquid saturation is a reasonable way to avoid defluidization. [Display omitted] • Pressure fluctuation analysis is used to study the fluidization of wet particles. • Bed changes from normal fluidization to slugging regime with increasing liquid saturation • The decreasing particle size intensifies the bubble behavior. • Reducing liquid saturation can repress the whole-bed slugging and defluidization. [ABSTRACT FROM AUTHOR]

An analysis from the results of investigation into spatial active damping of pressure fluctuations, vibrations, and vibration forces transferred from power facilities via expansion joints in their piping is presented. Vibration transfer from power facilities via piping can be several orders of magnitude greater than along the support structures. This fact should be kept in mind in designing vibration isolation of power equipment from the foundation and the environment through pipelines in the power and transport engineering, shipbuilding, and in oil and gas pipelines in pumping stations. To reduce the transfer of vibrations via a pipeline by means of vibration-isolating expansion joints, it is necessary to decrease their structural stiffness and the forces induced by fluctuations of the working fluid pressure in an expansion joint in a wide frequency band using structural or active methods. A review of the available publications has not revealed, except for the studies performed within the scope of this investigation, any analysis of the interaction between the fluid fluctuations and vibration in the expansion joints or information on reducing the transfer of vibrations and pressure fluctuations via expansion joints in liquid-carrying pipelines. The effectiveness of various multichannel spatial active vibration protection systems whose feedback circuit includes regulators in the form of standard band-pass filters has been studied experimentally. The effect that the interaction of active vibration force damping channels has on the damping efficiency, which may be caused by the cross sensitivity of three-component vibration force sensors during damping of the vibration forces, has been revealed. The active spatial vibration damping of a pipeline downstream of the expansion joint has also demonstrated the interaction of active vibration damping channels resulting in a noticeable change in the damping effectiveness. The effectiveness of the investigated options varied from 10 to 32 dB (reducing fluctuations, transfer of vibration, and forces transmission by 3–30 times) both at individual frequencies and in frequency bands in the range between 10 and 500 Hz. [ABSTRACT FROM AUTHOR]

When the pump-turbine operates at off-design conditions, vortex rope usually occurs in the draft tube and causes low-frequency pressure fluctuations. In this paper, the evolution of the vortex rope and its association with the low-frequency pressure fluctuations under typical operating conditions are investigated. The results indicate that: 1) The frequency of pressure fluctuation is mainly affected by the vortex's rotation frequency in the draft tube without cavitation. While when cavitation occurs, the frequency of pressure fluctuations in the draft tube is primarily affected by the cavitation volume evolution; 2) Under the non-cavitation condition, the overall vortex rope behaves as a spiral vortex rope under part-load condition, a slender column under design condition, and pear-shaped vortex rope under full-load condition. The vortex rope directly disappears when cavitation occurs under part-load condition. In contrast, the vortex rope becomes unstable, and changes from a single-phase vortex rope to a multi-phase vortex rope under the design condition. While at the full-load condition, the vortex rope becomes slenderer, and the rotation is more noticeable than under the non-cavitation condition. • A new multiphase flow simulation method is proposed and proved in pump-turbine. • The correlation mechanism between vortex and pressure fluctuations is revealed. • The spatial distribution law of low-frequency pressure fluctuations is studied. [ABSTRACT FROM AUTHOR]

The unsteady flow structures and pressure fluctuations of the cylinder-induced shock wave/boundary layer interactions (SBLIs) were investigated at Mach 3.4 and 3.8. The cylinders were mounted on the test section floor with a turbulent boundary layer, and six cylinders with various heights have been tested. The nanoparticle-based planar laser scattering (NPLS) flow visualization tests were performed, and the different features of shock systems as well as the "breath" effects of the separation bubble, have been validated by NPLS images. Dynamic pressure transducers were used to characterize the pressure fluctuations, and a remarkable spectra change was noticed around the cylinder foot. With increasing height, the PSD curve of x/D = − 1 ahead of the cylinder shaped from one-peak pattern to two-peaks pattern, while the second frequency peak showed a typical frequency of f ≈32 kHz. It was inferred that the first peak was more influenced by the free end of the cylinder and the detached shock. The second peak pattern of f ≈32 kHz was presumed to be affected by the vortex breakdown near the cylinder foot through analysis of flow visualization. Low frequency around 0 ~ 3 kHz was found to have an obvious rise at x/D = − 2, close to the typical frequency of SBLIs. [ABSTRACT FROM AUTHOR]

The transient behaviour of the pump-turbine in load rejection is very complex, and slight changes in runner blade shape may have great influence on it. To understand the underlying flow mechanisms, the load rejection processes of two model pump-turbines with the same specific-speed but different in the runner blade inlet shape were investigated by a three-dimensional numerical simulation method. The results show that the lean angle of the runner blade leading edge impacts the evolution of backflows at the runner inlet. The backflows first emerge at the shroud side for the runner with a negative lean angle, and the backflows first emerge at the hub side for the runner with no lean angle. However, the backflows at the shroud side make more imbalanced flows in the runner passages and higher increase of pressure fluctuations in the vaneless space. As a consequence, greater radial force fluctuations on the runner blades are formed. [ABSTRACT FROM AUTHOR]