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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]

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]

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]

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]

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.)

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]

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]

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]

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 main results of VTI's investigations into low-emission combustors for gas-turbine units (GTU) are presented. In recent years, the combustion of a premixed fuel-air mixture (FAM) in a swirling flow in a limited space has been under development for this purpose to attain more complete combustion, stable fluctuation-free operation of a combustor in a wide range of parameters, and compliance with environmental protection requirements. To solve the problems encountered in this field, a procedure has been developed for assessing the effect of temperature in the combustion zone, flow velocity, combustor pressure, and other factors on the combustion stability. A review is presented of a comprehensive approach employed by VTI's specialists to study the processes in combustors using numerical and experimental methods enabling them to cut down the cost and time of activities on development of low-emission combustors. For example, a relationship is presented between the numerically estimated quality of the produced fuel-air mixture and the experimental nitrogen oxide concentrations. A design parameter relating the process conditions in a flame tube with the vibration combustion amplitude is proposed. The experiments demonstrated a good correlation of the proposed parameter with measured pressure fluctuation amplitude. Of real interest are the presented examples of changes in the velocity and temperature fields with an increase in the working pressure, which should be considered in designing and bench testing the combustor. The low-emission combustors (LEC) developed for large- and medium-power GTUs are presented. The potential for scaling the combustors for other GTUs is examined. [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]

Purpose: The purpose of this paper is to analyze the effect of pressure fluctuations on the combustion efficiency of the hydrogen fuel injected into the supersonic oxidizing cross flow. The pressure fluctuations are imposed on inlet air flow and also on the fuel flow stream. Two different situations are considered: the combustion chamber once without and again with the inlet standing oblique shock wave. Design/methodology/approach: The pressure fluctuations are imposed on inlet air flow and also on the fuel flow stream. Two different situations are considered: the combustion chamber once without and again with the inlet standing oblique shock wave. The unsteady turbulent reacting flow solver is developed to simulate the supersonic flow field in the combustion chamber with detail chemical kinetics, to predict the time-variation of the combustion efficiency due to the imposed pressure fluctuations. Findings: The results show that the response of the reacting flow field depends on both the frequency of fluctuations and the existence of the inlet shock wave. In addition, the inlet standing shock wave has some attenuating role, but the reacting flow shows an amplifying role on imposed oscillations which is also augmented by imposing anti-phase fluctuations on both inlet and fuel flow streams. Originality/value: This study is performed to analyze the instabilities in the supersonic combustion which has not been considered before in this manner. [ABSTRACT FROM AUTHOR]

The aim of this study is to characterize the steady and unsteady flows of a high‐speed axial fan stage and assess its aerodynamic performance parameters. The flow unsteadiness is related to the stator‐rotor interaction originated mainly by two mechanisms: the first is attributed to the potential effect and the second to the wake‐blade interaction and the mixing through the blades' passages. Such effects are dependent on the circumferential positions of blades and inter‐distance between stator and rotor, which could be alleviated by understanding these flow interactions. The pressure waves' main diametrical modes (two blades interacting with two vanes) and their sequences are predicted analytically. FFT analysis of the computed static pressure fluctuations at different monitor points allowed identifying the prevailing modes of interaction and their frequencies and sequence. The assessment of inter‐distance is an important step toward identifying the detrimental effects of axial interdistance on the aerodynamic performance. The closer the blade‐rows of this fan stage can be spaced, the more compact the cooling system of an automotive could be designed. [ABSTRACT FROM AUTHOR]

A new parameter (degree of randomness (DR)) was defined for the identification of the main transition velocities, Utrans. The new method reconstructs the time series into multiple state vectors, thus generating non‐overlapping vector pairs and then compares the distance between them with a pre‐selected cut‐off length. The DR values were extracted from gauge and differential pressure fluctuations as well as x‐ray tomographic scans. At every Utrans value, the DR index exhibited a well‐pronounced local minimum. Three cylindrical bubble columns (BCs) with various diameters (0.1, 0.14, and 0.45 m in ID) and one rectangular BC (width = 0.2 m, depth = 0.04 m) were used. They were aerated by means of different perforated plate gas distributors. It was found that in the cylindrical BCs the disintegration of the bubbly flow regime took place always at Utrans = 0.04 m/s. In the case of the rectangular BC the first critical velocity appeared at Utrans = 0.012 m/s. The lower boundary of the churn‐turbulent regime was identified at Utrans = 0.11 m/s in the smallest cylindrical BC and at about Utrans = 0.095 m/s in the other two cylindrical BCs. In the case of the rectangular BC, the second critical velocity was identified at Utrans = 0.039 m/s. The low Utrans in the rectangular BC imply that the hydrodynamic regimes are less stable in this particular column due to higher degree of liquid turbulence. The calculated DR values from the gauge pressure fluctuations successfully distinguished the upper boundary of the gas maldistribution and the first transition sub‐regime. [ABSTRACT FROM AUTHOR]

The recent advances in centrifugal pump design do not only require a better suction performance but also there have been attempts to reduce design time at a lower cost. The traditional trial-and-error optimization design method, however, depends on the designer's experience, which requires longer cycles. This is because the computational process of calculating the net positive suction head required (NPSHr) involves several calculation steps and this consumes a lot of computational time. An investigation was therefore carried out to test a novel NPSHr prediction method in a double-suction centrifugal pump using unsteady numerical simulations. In the new approach, a new boundary pair was introduced and an algorithm was used to estimate a good value for a static pressure value that correlates to a 3% drop in pump head to determine the critical cavitation point. Experiments were conducted to validate the hydraulic performance and the cavitation model. The NPSHr and the characteristic "sudden" head-drop were very well predicted by the novel approach in only three simulation steps. The internal flow analysis showed that for 0.6 Q d , the flow around the volute tongue was uneven at NPSH = 10.06 m, inducing flow separation and recirculation at the tongue region. Attached cavities were also observed around the suction ring in the spiral suction domain. The pressure fluctuations were analyzed also and the dominant frequency at the pump outlet and tongue region was the blade passing frequency. Consequently, the novel approach proved very robust and efficient in NPSHr prediction and would be a good alternative to shorten simulation time during cavitation optimization design process in centrifugal pumps. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Reports is the property of Wiley-Blackwell 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 the experiments performed on a high head model Francis turbine during start-up. Synchronized time dependent pressure and velocity measurements were performed to investigate the instabilities in the turbine. A total of four steady state operating points, namely synchronous load, part load, best efficiency point, and high load are considered to perform the turbine start-up. The runner angular speed was observed to increase almost exponentially during the guide vane positions from completely closed to no load condition. The frequency of wave propagation due to the interaction between runner blades and guide vanes was observed to follow the trend of increase of runner angular speed. A vortex rope frequency was captured in the draft tube during synchronous load to part load of the start-up. Two different mechanisms, namely, the development of stagnation point and the available recirculation regions were observed to cause the formation of vortex rope in the draft tube. [ABSTRACT FROM AUTHOR]

Pressure fluctuations that cause acoustic radiation from vessel models with concentric and eccentric blunt stenoses are investigated. Large eddy simulations of non-pulsatile flow condition are performed using OpenFOAM. Calculated amplitude and spatial-spectral distribution of acoustic pressures at the post-stenotic region are compared with previous experimental and theoretical results. It is found that increasing the Reynolds number does not change the location of the maximum root mean square wall pressure, but causes a general increase in the spectrum level, although the change in the shape of the spectrum is not significant. On the contrary, compared to the concentric model at the same Reynolds number, eccentricity leads to an increase both at the distance of the location of the maximum root mean square wall pressure from the stenosis exit and the spectrum level. This effect becomes more distinct when radial eccentricity of the stenosis increases. Both the flow rate and the eccentricity of the stenosis shape are evaluated to be clinically important parameters in diagnosing stenosis. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature 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.)

In centrifugal pumps, it is important to select appropriate turbulence model for the numerical simulation in order to obtain reliable and accurate results. In this work, ten turbulence models in 3-D transient simulation for the centrifugal pump are chosen and compared. The pump performance is validated with experimental results. The numerical results reveal that the SST turbulence model was closer to the experimental results in predicting head. In addition, the pressure variation trend for the ten models is very similar which increases and then decreases from the inlet to outlet of the pump along the streamline. The SST k-ω model predicts the performance of the pump was more accurately than other turbulent models. Furthermore, the results also found that the error is the least at design operation condition 300(l/min), which is around 1.98 % for the SST model and 2.14 % and 2.38 % for the LES and transition omega model. Within 7.61 %, the errors at higher flow rate 350(l/min) for SST. The error for SST model is smaller as compared to different turbulent models. For the Realizable k-ɛ model, the errors fluctuate were more high than other models. [ABSTRACT FROM AUTHOR]

Fluid-flow and pressure fluctuation are main causes of vibration and noise in liquid-conveying pipeline. As a crucial auxiliary component of liquid-conveying pipeline, the bladder pressure fluctuation attenuator plays an important role in absorbing fluctuations. According to the working condition, reasonable selection of attenuator parameters can give full play to the maximum efficiency of the attenuator so as to reduce pressure fluctuation of the pipeline. Based on the stress model of the attenuator, the mathematical and simulation models of the attenuation device are established by suitable hypothesis and simplification, and based on the calculation and physical models provided by FLUENT software, the movement of bladder was simulated by dynamic mesh and UDF (user-defined function). The absorption effect of attenuator on pipeline pressure fluctuation was investigated under different inflating pressures and frequencies. The results show that reasonable selection of initial pressure of the attenuator can effectively reduce the pressure fluctuation of pipeline fluid. Compared with the theoretical analysis results, the simulation results are more close to the experimental results, and the validity of the simulation model is verified, and a method and new idea are provided for the future study of the parameters of the bladder pressure fluctuation attenuator. [ABSTRACT FROM AUTHOR]

To fully understand the evolution of flow structures and pressure fluctuations in the S-shaped region of pump-turbines, three dimensional (3D) numerical simulations were carried out for a model pump-turbine at four different guide-vane openings (GVOs). We found that special backflow vortex structures (BFVSs) form around the runner inlet. The backflow location shifts from the hub side to the shroud side and then to the midspan, as the operating point moves from the best efficiency point to the zero discharge point along the S-shaped characteristic curve. At large GVO, if the discharge is relatively large, the flow separations at the runner inlet are primarily driven by the local adverse pressure gradient, resulting in hub and shroud side backflows. At small GVO or small discharge, the separations are mainly dominated by the centrifugal force, resulting in backflow at the guide-vane midspan section. The locally distributed BFVSs enhance the local rotor-stator interaction (RSI) in the vaneless space, leading to different pressure fluctuating intensities along the spanwise direction for high frequency components. On the other hand, the rotating stall is the main cause of the uneven distributions of low frequency pressure fluctuations along the vaneless space between runner and guide-vanes. [ABSTRACT FROM AUTHOR]

Parametric experimental investigations of the fields of turbulent wall pressure fluctuations on the surface of steps are performed. A considerable effect of the obstacle height on the spectral composition of the pressure fluctuations behind the leading edge is shown. The transformation of the spectral composition at different observation points is illustrated. The influence of the boundary layer thickness and the sweep angle is shown to be relatively weak. The spatial variation of the local correlation scales and the convective properties of the pressure fluctuation field on the step surface is illustrated. [ABSTRACT FROM AUTHOR]

Hydraulic pressure fluctuation energy harvesters are promising alternatives to power up wireless sensor nodes in hydraulic systems. The characterization of these harvesters under dynamic and band-limited pressure signals is imperative for the research and development of novel concepts. To generate and control these signals in a hydraulic medium, a versatile apparatus capable of reproducing pressure signals is proposed. In this paper, a comprehensive discussion of the design considerations for this apparatus and its performance is given. The suggested setup enables the investigation of devices tailored for the harvesting of energy in conventional hydraulic systems. To mimic these systems, static pressures can be tuned up to 300 bar, and the pressure amplitudes with a maximum of 28 Bar at 40 Hz and 0.5 bar at 1000 Hz can be generated. In addition, pressure signals found in commercial hydraulic systems can be reproduced with good accuracy. This apparatus proves to be an accessible, robust, and versatile experimental setup to create environments for the complete performance estimation of pressure fluctuation energy harvesters. [ABSTRACT FROM AUTHOR]

The effect of cohesive particles on the pressure fluctuations was experimentally investigated in a binary gas-solid fluidized bed. The pressure fluctuation signals were measured by differential pressure sensors under conditions of various weight percentages of cohesive particles. The cohesive particles increased the fixed bed pressure drop per unit height and decreased the minimum fluidization velocity. The Wen & Yu equation well predicts the minimum fluidization velocity of the binary system. The addition of cohesive particles slightly decreased the bubble size in bubbling flow regime when the cohesive particles and the coarse particles mixed well, while the bubble size greatly decreased when the cohesive particles agglomerated on the bed surface. The time series of pressure fluctuations was analyzed by using the methods of time domain, frequency domain and wavelet transformation. The normalized standard deviation of pressure fluctuations decreased with increasing weight percentages of cohesive particles. A wide bandwidth frequency of 0 to 1Hz got narrower with a single peak around 0.6Hz with an increase in proportion of the cohesive particles. The meso-energy and micro-energy of pressure fluctuations were decreasing with increasing cohesive particles proportions, which indicated that adding cohesive particles could reduce the energy dissipation of bubble and particle fluctuations. [ABSTRACT FROM AUTHOR]

To elucidate the characteristics and generation mechanism of pressure fluctuations in single-channel pumps, the unsteady flow in three single-channel pumps with the same impeller equipped with a spiral volute (model 1), a circular volute (model 2), and a torus (model 3) were analyzed by computational fluid dynamics. Experiments on global performance characteristics in the volute of model 1 were performed, and fast response pressure sensors were installed in the spiral volute to measure pressure fluctuations. The results indicate that the numerical results are in good agreement with the experimental results. This study shows that a phase delay exists between different volute monitoring points and the pressure fluctuations in the volute are mainly caused by the potential interactions between the impeller blade and volute wall. Comparison of the pressure fluctuations amplitude of the impeller outlet shows that pressure fluctuation amplitude of model 3 is one order of magnitude lower than those of the others and the wake at the impeller outlet played an important role in pressure fluctuations. The standard deviation of pressure was introduced to describe the pressure fluctuations strength. It shows that the pressure fluctuation strength of the pressure surface is apparently higher than that of the suction surface, and the maximum pressure fluctuation strength in the blade is consistent with the flow separation area, indicating that flow separation is also an important factor for pressure fluctuations in single-channel pumps. [ABSTRACT FROM AUTHOR]

This is the second paper in a series of publications summarizing the international experience in the development of low-emission combustors (LEC) for land-based, large (above 250 MW) gas-turbine units (GTU). The purpose of this series is to generalize and analyze the approaches used by various manufacturers in designing flowpaths for fuel and air in LECs, managing fuel combustion, and controlling the fuel flow. The efficiency of advanced GTUs can be as high as 43% (with an output of 350-500 MW) while the efficiency of 600-800 MW combined-cycle units with these GTUs can attain 63.5%. These high efficiencies require a compression ratio of 20-24 and a temperature as high as 1600°С at the combustor outlet. Accordingly, the temperature in the combustion zone also rises. All the requirements for the control of harmful emissions from these GTUs are met. All the manufacturers and designers of LECs for modern GTUs encounter similar problems, such as emissions control, combustion instability, and reliable cooling of hot path parts. Methods of their elimination are different and interesting from the standpoint of science and practice. One more essential requirement is that the efficiency and environmental performance indices must be maintained irrespective of the fuel composition or heating value and also in operation at part loads below 40% of rated. This paper deals with Mitsubishi Series M701 GTUs, F, G, or J class, which have gained a good reputation in the power equipment market. A design of a burner for LECs and a control method providing stable low-emission fuel combustion are presented. The advantages and disadvantages of the use of air bypass valves installed in each liner to maintain a nearly constant air to fuel ratio within a wide range of GTU loads are described. Methods for controlling low- and high-frequency combustion instabilities are outlined. Upgrading of the cooling system for the wall of a liner and a transition piece is of great interest. Change over from effusion (or film) cooling to convective steam cooling and convective air cooling has considerably increased the GTU efficiency. [ABSTRACT FROM AUTHOR]

Alternating electric field was used as an external assistance method to enhance the quality of fluidization of nanoparticles. The electric field was applied to the bed using two parallel electrodes, one grounded and AC voltage applied to the other. Varying electric field strength in the range of 0–1 kV/cm was used in the experiments. Hydrophilic TiO2 nanopowder was used as the bed material. The bed was fluidized with either pure nitrogen or nitrogen containing isopropanol vapour. It was found that increasing the alternating electric field strength decreases the minimum fluidization velocity, bubble size, and agglomerate size. Adding isopropanol vapour to the fluidizing gas decreases the minimum fluidization velocity, bubble size, and agglomerate size, compared to fluidization with dry nitrogen, at the same field strength. It is shown that increasing the alternating electric field strength increases the voidage of the bed at minimum fluidization and decreases the voidage of agglomerates. [ABSTRACT FROM AUTHOR]

The operation of an acoustic transducer in a temperature-stratified medium is investigated. The formation of a response of piezoceramic transducers of pressure fluctuations under the action of temperature fluctuations in a working medium on the sensor element is considered. The attenuation of the temperature signal of a pressure transducer in a turbulent boundary layer is calculated numerically. The effect of distortions of the spectral levels of pressure fluctuations detected by a sound transducer in the field of temperature inhomogeneities is investigated for the example of measurements of turbulent pressure fluctuations in a boundary layer during vertical ascent of the device to the surface from a specified depth in a deep sea. [ABSTRACT FROM AUTHOR]

A computational model of inhomogeneous pressure-fluctuation fields in the vicinity of a forwardfacing step-backward-facing step configuration taking into account the high degree of their mutual correlation (global correlation) is generalized from experimental data. It is shown that when determining the characteristics of pressure fluctuations that act on an elastic structure, the global correlation is represented by an additional inhomogeneous field. It is demonstrated that a high degree of correlation may lead to a significant change in the main characteristics of the pressure-fluctuation field in the wake behind the configuration. This is taken into consideration in the model by correcting the local properties of this field. [ABSTRACT FROM AUTHOR]

In this work, the effect of distributor type on fluidized bed hydrodynamics was studied by taking into account time, frequency, and state space domains. For this purpose, pressure fluctuations were measured in a fluidized bed with 0.15 m diameter and the experiments were carried out for three different types of distributors (perforated plate, bubble cap, and porous plate) at different sizes and various superficial gas velocities and particle sizes. Time domain analysis demonstrated that while the initial bubble size on the bubble cap distributor is greater than that on the perforated plate, the standard deviation of pressure fluctuations is greatest in a bed equipped with the porous plate, followed by the perforated plate and then the bubble cap distributor. Based on the current analysis and in view of the frequency domain analysis, it was found that the contribution of finer structures (small bubbles and clusters) is highest for a porous plate, followed by a bubble cap and then a perforated plate distributor. Also, according to the S-statistic method, it was concluded that the S-test is a reliable method for detection of differences between hydrodynamic situations of fluidized beds, while different types of distributors were used. [ABSTRACT FROM AUTHOR]

This paper examines the flow field of a circular-arc gear pump operating at high pressures and high speeds by the commercial finite-volume-based code Fluent. The performance of circular-arc gear pump operating at high pressures and high speeds have been discussed. The mathematical model of the tooth profile is established. The pressures including gears mesh, outlet pressures, and outlet flow rate are studied under different rated outlet pressures and rotational speeds. There are dynamic pressures at clearance between chamber and tip circle of gear. Moreover, parts of radial leakages are prevented by dynamic pressures. The outlet pressures almost remain constant. However, there are strong pressure fluctuations in gears mesh under the high pressures and high speeds. The pressures are several times higher than the rated outlet pressure when the circular-arc gear pump operates at 10,000 r/min and 12,000 r/min. Gear meshing pressure fluctuations increase with the increase in rotational speeds. However, gear meshing pressure fluctuations decrease with the increase of outlet rate pressures. There are rotational speeds and outlet rate pressure critical points for gear meshing pressures, and the variation tendency of gear meshing pressures changes dramatically when it exceeds the critical points. Hence, the research results provide base model for circular-arc gear pump operating at high pressures and high speeds. [ABSTRACT FROM AUTHOR]

Wang, L.; Guo, C.; Su, Y.; Wu, T., and Wang, S., 2017. Numerical study of the viscous flow field mechanism for a non-geosim model. Inasmuch as the scale effect of wake fields has not yet been resolved, the application of a 'Smart Dummy' model in predicting the full-scale nominal wake field and propeller-induced hull pressure fluctuations of ships sailing in coastal environments and zones farther out to sea has shown great potential since the concept was first proposed. However, it still has not been widely used because the rules and mechanisms of the Smart Dummy model are seldom studied by international and domestic researchers. A non-geometrically similar model (non-geosim model) of the KRISO3600TEU Container Ship (KCS) was designed by employing a local parameterization modeling method based on computational fluid dynamics numerical simulation methods. Based on the viscous flow field mechanism, numerical analysis was performed on the ship resistance performance, free-surface wave pattern, hull volume-of-fluid distribution, hull streamlines, nominal wake field at the propeller plane, and stern axial velocity field. First, the accuracy of meshing and numerical methods was verified using grid-independent analysis. Subsequently, the same grid and methods were applied for the numerical simulation and analysis of towed bare hull and self-propelled ships. The results show that the free-surface wave pattern of the Smart Dummy model was almost identical with that of the geosim model, and the distribution of boundary layers around the hull shows that the Smart Dummy had thinner and more contracted velocity boundary layers after the deformation area. The stern streamline distribution further indicated that the Smart Dummy model had a more uniform propeller inflow velocity. The difference in the angle of attack of the propeller blade operating at the rear of the KCS model accounted for the overprediction of the propeller-induced hull pressure fluctuations using the geosim model. Overall, the new method proposed in this paper has important potential applications in predicting flow characteristics for large container ships sailing in coastal environments and zones farther out to sea. [ABSTRACT FROM AUTHOR]

Results of experimental investigations of the parameters of an element of a wave filter the structural design of which is based on the location of the pressure fluctuation detector in a cavity beneath a fine-mesh grid are presented. The optimal dimensions of the element at which maximal averaging of short wavelengths may be achieved are presented. A method of determining the efficiency of the filter is proposed. [ABSTRACT FROM AUTHOR]