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The general solutions for nonlinear waves in a bubble-liquid mixture are obtained from the Kudryashov–Sinelshchikov (KS) equation under different parametric regimes. The Chiellini integrability condition has been used for constructing exact general solutions. In the non-dissipative case, we find that the solutions may be expressed in terms of Jacobi elliptic and Weierstrass functions. On the other hand, in the dissipative case, only implicit solutions are obtained for the KS equation. For an alternative perspective, the notion of the Jacobi Last Multiplier has been utilized to obtain the corresponding Lagrangian and Hamiltonian description of the reduced equation for the bubble-liquid mixture system. [ABSTRACT FROM AUTHOR]

Turbomachinery shock wave patterns occur as a natural result of operating at off-design points and are accountable for some of the loss in performance. In some cases, shock wave–boundary layer (SW-BLIs) interactions may even lead to map restrictions. The current paper refers to experimental findings on a transonic linear cascade specifically designed to mitigate shock waves using porous walls on the blades. Schlieren visualization reveals two phenomena: Firstly, the shock waves were dissipated in all bladed passages, as predicted by the CFD studies. Secondly, a lower-pressure wave pattern was observed upstream of the blades. It is this phenomenon that the paper reports and attempts to describe. Attempts to replicate this pattern using Reynolds-averaged Navier–Stokes (RANS) calculations indicate that the numerical method may be too dissipative to accurately capture it. The experimental campaign demonstrated a 4% increase in flow rate, accompanied by minimal variations in pressure and temperature, highlighting the potential of this approach for enhancing turbomachinery performance. [ABSTRACT FROM AUTHOR]

Modulated pressure waves propagating in the drilling fluids inside the drill string are a reliable real-time communication technology that transmit data from downhole to the surface during oil and gas drilling. In the analysis of pressure waves' propagation characteristics, the modeling of transient friction in non-Newtonian fluids remains a great challenge. This paper establishes a numerical model for transient pipe flow of power-law non-Newtonian fluids by using the weighted residual collocation method. Then, the Newton–Raphson method is applied to solve the nonlinear equations. The numerical method is validated by using the theoretical solution of Newtonian fluids and is proven to converge reliably with larger time steps. Finally, the influencing factors of the wall shear stress are analyzed using this numerical method. For shear-thinning fluids, the friction loss of periodic flow decreases with the increase in flow rate, which is opposite to the variation law of friction with the flow rate for stable pipe flow. Keeping the amplitude of pressure pulsation unchanged, an increase in frequency leads to a decrease in velocity fluctuations; therefore, the friction loss decreases with the increase in frequency. [ABSTRACT FROM AUTHOR]

This article discusses the problem of combating pressure fluctuations in the suction line of piston compressors. As you know, incorrect calculation of communications can lead to accidents of compressor equipment. Therefore, special attention must be paid to the layout of pipelines and equipment, while avoiding resonance phenomena. One way to combat pressure pulsations in the suction line is to install diaphragms. This method is the cheapest and easiest to implement, especially for compressors already in operation. The experimental studies carried out confirmed the known data that the area of the diaphragm opening should be four times smaller than the diameter of the pipeline. At the same time, a threefold reduction in the amplitude of pressure fluctuations is achieved. Installation of a diaphragm design with parameters close to the recommended ones is possible anywhere in the suction line, since the change in amplitude at different pressure from the suction valves does not exceed 5...7 %. When installing a diaphragm with dimensions different from those recommended, it is necessary to install it closer to the suction valve.

Sheet-to-cloud cavitation transitions are very complex owing to the simultaneous appearance of the re-entrant jet and shock waves. The objective of this paper is to investigate the physics of compressible cavitating flows with emphasis on the simultaneous existence of the re-entrant jet and shock waves. A compressible cavitating solver, which considers the compressibility effects of both the liquid and the vapour, was used to account for the different shedding characteristics induced by the re-entrant jet mechanism (RJM), the shock wave mechanism (SWM), and both the re-entrant jet and the shock waves (RJM-SMW). The solver used Large Eddy Simulations (LES) and the Schnerr-Sauer cavitation model. The numerical results are first compared with available experimental data [1] which showed satisfactory agreement for various aspects of the flow, including the pressure distribution, cavity shapes, condensation front speed, and shedding frequency. The results first show three different cavity shedding processes induced by the re-entrant jet and the shock waves. Frequency analyses show that the shock waves produce a wider frequency distribution which indicates that shock waves induce more shedding than the re-entrant jet. The quasi-periodic characteristics of the transitions between the various cavity shedding characteristics are mainly induced by the variations of the pressure, residual cavity volume and medium compressibility. Further analyses show that the different pressure, residual cavity volume and medium compressibility amplitudes determine the cavity shedding characteristics in the subsequent shedding cycle. When the conditions favour both the re-entrant jets and the shock wave effects, both the re-entrant jet and the shock waves impact the cavity shedding. [ABSTRACT FROM AUTHOR]

Turbomachinery shock wave patterns occur as a natural result of operating at off-design points and are accountable for some of the loss in performance. In some cases, shock wave–boundary layer (SW-BLIs) interactions may even lead to map restrictions. The current paper refers to experimental findings on a transonic linear cascade specifically designed to mitigate shock waves using porous walls on the blades. Schlieren visualization reveals two phenomena: Firstly, the shock waves were dissipated in all bladed passages, as predicted by the CFD studies. Secondly, a lower-pressure wave pattern was observed upstream of the blades. It is this phenomenon that the paper reports and attempts to describe. Attempts to replicate this pattern using Reynolds-averaged Navier–Stokes (RANS) calculations indicate that the numerical method may be too dissipative to accurately capture it. The experimental campaign demonstrated a 4% increase in flow rate, accompanied by minimal variations in pressure and temperature, highlighting the potential of this approach for enhancing turbomachinery performance.

In this study, the sliding grid method is used to simulate a 350 km/h high-speed train passing through a 350 m standard single-line tunnel. The cross-sectional pressure distribution ahead of the train is investigated, the three-dimensional characteristics and propagation mechanism of pressure waves are described based on iso-pressure surfaces, and a newly accurate pressure sensor layout is proposed. The results show that the farther the cross-section is from the train, the smaller the cross-sectional pressure difference is. Influenced by the shape of the train nose and tunnel cross-section, the pressure waves are not simple planar waves, but spherical waves that vary in complexity over the propagation process. As the pressure difference of the 16.6 m cross-section before the train is within 1 Pa, the pressure waves behind this cross-section are defined as planar waves. Besides, the pressure peak-to-peak value difference between the wall and construction clearance reaches 13% at 70–90 m cross-sections, so the pressure sensors should be placed on the surface of the appurtenances rather than on the tunnel wall. In summary, this study is significant for understanding the formation and transmission mechanisms of pressure waves and guiding the scientific layout of pressure sensors in tunnels. [ABSTRACT FROM AUTHOR]

Modulated pressure waves propagating in the drilling fluids inside the drill string are a reliable real-time communication technology that transmit data from downhole to the surface during oil and gas drilling. In the analysis of pressure waves’ propagation characteristics, the modeling of transient friction in non-Newtonian fluids remains a great challenge. This paper establishes a numerical model for transient pipe flow of power-law non-Newtonian fluids by using the weighted residual collocation method. Then, the Newton–Raphson method is applied to solve the nonlinear equations. The numerical method is validated by using the theoretical solution of Newtonian fluids and is proven to converge reliably with larger time steps. Finally, the influencing factors of the wall shear stress are analyzed using this numerical method. For shear-thinning fluids, the friction loss of periodic flow decreases with the increase in flow rate, which is opposite to the variation law of friction with the flow rate for stable pipe flow. Keeping the amplitude of pressure pulsation unchanged, an increase in frequency leads to a decrease in velocity fluctuations; therefore, the friction loss decreases with the increase in frequency.

Hydraulic transient analysis allows the condition assessment of pipeline systems by the measurement of a system's transient pressure response subject to input pressure excitations. The detection of a pressure wave's arrival time and amplitude at one or more sections can be used to detect unexpected anomalies, such as leaks, blockages, or corroded sections. Wave separation approaches, based on signal processing techniques involving two sensors, enable a directional attribution to any measured pressure perturbations. Being able to determine the direction of origin of a perturbation through a signal-splitting approach greatly facilitates anomaly detection through the resolution of this ambiguity. The signal-splitting procedure can be sensitive to the analysis conditions (i.e. the signal processing procedure used, the presence of noise within the signal, and the spacing of the sensors) and, as a result, produce spurious results. This paper explores this issue and proposes, and analyses, a range of strategies to improve the signal-splitting results. The strategies explored involve the consideration of alternative time- and frequency-domain formulations; the use of filters and wavelet to condition the signal; and processing the time-shifted differenced signal as opposed to the original raw signal. Results are presented for a range of numerical and laboratory systems. HIGHLIGHTS The pressure signals acquired at two measurement sections can be separated, pointing out positive and negative traveling wave components.; The separation procedure can be helpful in the transient-based diagnosis in complex systems.; Different techniques are developed in time and frequency domains and tested on numerical and laboratory experiments.; Wavelet transform of separated signals is also derived.;

Copyright of Chinese Journal of Explosives & Propellants is the property of Chinese Journal of Explosives & Propellants 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 paper shows the occurrence of pressure waves and their propagation in the equipment of the first circuit of the WWER-1000 reactor plant in emergency situations associated with an instantaneous stop of the Main circulation pump or a two-way flow with an instantaneous two-way break in the cold thread of the main circulation pipeline. The influence of the time of initialization of the accident (pump stop, pipeline rupture) on the intensity of the process-amplitude, frequency of pressure changes is investigated. Pressure drops during an emergency on the main elements of the circuit are considered. It is shown that the maximum changes in the amplitude and frequency of both the pressure and the pressure drops on the circuit elements belong to the initial stage of the accident. The main attention is focused on the pressure drops on the equipment, because this parameter determines the dynamic loads on the equipment, which can lead to its failure.

The Hyperloop system is a new and innovative mode of transportation in which high-speed pods move through near-vacuum tubes. The multi-pod Hyperloop Systems are essential for increased transportation capacity. In this study, a multi-pod Hyperloop System was analyzed using numerical simulations at different values of the distance between the pods (i.e., 2 L–3.5 L). The pressure and velocity flow fields and the aerodynamic characteristics of the pods were analyzed for four different flow speeds, that is, 100, 200, 300, and 400 m/s, using unsteady compressible flow conditions. The simulation results indicated that the pressure waves generated across the pods play a significant role in the determination of the aerodynamic characteristics of the pods. Increasing the distance between the pods results in the delay of the pressure wave interaction. The aerodynamic drag increases on the first pod with the increase in the distance between the pods due to an increase in the pressure gradient. In contrast, the aerodynamic drag decreases across the second pod with the increase in the distance between them. So, the distance between the pods is a critical factor that should be considered when designing the Hyperloop System with more than one pod. [ABSTRACT FROM AUTHOR]

A hydrogen/air flame propagation and the development of tulip-shaped flame in 2D tubes of different aspect ratios with both closed ends and in a half-open rectangular channel were studied using high resolution direct numerical simulations of the fully compressible Navier – Stokes equations coupled with a detailed chemistry. Flame propagation in a 3D rectangular channel was studied using large eddy simulations and compared with the results of direct numerical simulations of flame propagation in a 2D rectangular channel with the same aspect ratio. It is shown that the interaction of the rarefaction wave generated by the flame at the deceleration stage with the "positive" flow of unburned gas generated by the flame at the previous accelerating stage leads to a significant decrease of the velocity of the unburned gas flow in the near field zone ahead of the flame front. As a result, the thickness of the boundary layer in the near-field zone ahead of the flame increases significantly, and the profile of the axial velocity of the unburned gas in the near-field zone ahead of the flame front takes the form of a tulip or an inverted tulip, which leads to corresponding changes in the velocities of different parts of the flame front, the flame front inversion, and the formation of a tulip-shaped flame. [ABSTRACT FROM AUTHOR]

This article considers the generation of pressure waves during the combustion of hydrogen–air clouds in various modes. The problem of the combustion of spherical clouds, in which the inner spherical volume burns with an apparent velocity of 240 m/s, and the remaining outer layer with an apparent velocity of 100 m/s, is considered. Also, for comparison, two limiting cases are considered: the combustion of the entire cloud with constant velocities of 100 and 240 m/s. The problem is solved numerically in a one-dimensional formulation, with the combustion front clearly identified. As a result, using precise numerical simulation, it is shown that the deflagration of secondary volumes of hydrogen–air mixtures in an open space at a slow speed (up to 100 m/s) does not lead to an increase in pressure in the waves generated earlier during the deflagration of the primary volume at a fast speed corresponding to deflagration in an obstructed space. Such a situation is observed for the inner region of various sizes (the portion of the cloud that burns at a high rate). [ABSTRACT FROM AUTHOR]

Various potential causes of damping of pressure waves in water-hammer-like flows are discussed, with special attention being paid to their qualitative influences on measured pressure histories. A particular purpose is to highlight complications encountered when attempting to interpret causes of unexpected behaviour in pipe systems. For clarity, each potential cause of damping is considered in isolation even though two or more could exist simultaneously in real systems and could even interact. The main phenomena considered herein are skin friction, visco-elasticity, bubbly flows and porous pipe linings. All of these cause dispersive behaviour that can lead to continual reductions in pressure amplitudes. However, not all are dissipative and, in such cases, the possibility of pressure amplification also exists. A similar issue is discussed in the context of fluid–structure interactions. Consideration is also given to wavefront superpositions that can have a strong influence on pressure histories, especially in relatively short pipes that are commonly necessary in laboratory experiments. For completeness, attention is drawn towards numerical damping in simulations and to a physical phenomenon that has previously been wrongly cited as a cause of significant damping. [ABSTRACT FROM AUTHOR]

• A low Mach compressible two-phase flow solver using a single fluid formulation is presented. • A pressure-based method for compressible flows and CLSVOF algorithm to capture the sharp interface is employed. • The method can handle different combinations of incompressible and compressible phases. • A detailed qualitative and quantitative validation of the method is presented. In this study, a low Mach, pressure-based solver is developed for simulation of compressible two-phase flows. The two-dimensional solver developed on collocated grids in a finite volume framework adopts a unified formulation to efficiently handle different combinations of the two phases, including the cases where compressible and incompressible phases coexist. The pressure-based solver is coupled to a sharp interface capturing approach based on the coupled level set and volume of fluid method, which can accurately account for surface tension. The energy equation considered in the framework also accounts for dissipative effects due to viscosity and heat conduction. A variety of representative test cases of increasing complexity are considered to evaluate the performance of the solver in simulating compressibility effects while accurately resolving the interface. The results for Rayleigh-Taylor instability exhibit equivalent performance in both incompressible and low Mach regimes, while accounting for thermal effects arising due to compressibility. An isothermal bubble compression case due to a velocity field shows excellent agreement with existing results. The numerical results of bubble oscillations immersed in an incompressible liquid validated with one-dimensional and two-dimensional Rayleigh-Plesset model at different density ratios depict the ability of the unified approach to handle pressure waves effectively. This is further demonstrated by simulating bubble expansion inside an incompressible fluid due to decaying pressure. [ABSTRACT FROM AUTHOR]

A liquid mercury target, which is used to explore the neutrons produced by spallation reactions, has been installed at the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). As the proton beams bombard the target, pressure waves are generated on the interface between liquid and solid metals due to thermal shock. The negative-pressure-induced cavitation causes severe pitting damage to the vessel surface of the mercury target. To reduce the surface damage of the mercury target and prolong its service life, we developed vibratory horn experiments in bubbly water. In this study, the effect of microbubbles on cavitation damage on the workpiece surface was investigated using ultrasonic erosion tests. Experimental results showed that surface damage was significantly reduced under the condition of injecting microbubbles. Additionally, we developed a simulation code to analyze the change in pressure waves in the water. The analysis results showed that the pressure amplitude of the pressure waves was significantly reduced under the condition of injecting microbubbles, and the fluctuation of the pressure waves became more regular when injecting microbubbles. We also found that the pressure amplitude of the pressure waves was decreased with a decrease in the diameter of the microbubbles. [ABSTRACT FROM AUTHOR]

Mathematical models of the dynamics of rigid particles during wave reconstruction of the hydrodynamic relation between a hole and a formation are considered. The conditions for cleaning productive rock from colmatant in the wave field of repression and depression are determined. The results of applying the technologies and equipment in the mode of depression-wave cleaning of the bottom-hole formation zone are given. [ABSTRACT FROM AUTHOR]

Copyright of Vatten is the property of Foreningen Vatten 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.)

Within the framework of Classical Continuum Thermomechanics, we consider an unsteady isothermal flow of a simple isotropic linear viscous fluid in the liquid state to investigate the transient flow conditions. Despite the attention paid to this problem by several research works, it seems that the understanding of turbulence in these flow conditions is controversial. We propose a dimensionless procedure that highlights some aspects related to the transition from viscous to turbulent flow which occurs when a finite amplitude pressure wave travels through the fluid. This kind of transition is demonstrated to be described by a (first) dimensionless number, which involves the bulk viscosity. Furthermore, in the turbulent flow regime, we show the role played by a (second) dimensionless number, which involves the turbulent bulk viscosity, in entropy production. Within the frame of the 1D model, we test the performance of the dimensionless procedure using experimental data on the pressure waves propagation in a long pipe (water hammer phenomenon). The obtained numerical results show good agreement with the experimental data. The results' inspection confirms the predominant role of the turbulent bulk viscosity on energy dissipation processes. [ABSTRACT FROM AUTHOR]

The threat of accidental hydrocarbon explosions is of major concern to industrial operations; in particular, there is a need for design tools to assess and quantify the effects of potential deflagration events. Here we present a design methodology based on analytical models that allow assessing the loading and structural response of objects exposed to pressure waves generated by deflagration events. The models allow determining: i) the importance of Fluid-Structure Interaction (FSI) effects; ii) the transient pressure histories on box-like or circular cylindrical objects, including the effects of pressure clearing; iii) the dynamic response of structural components that can be idealised as fully clamped beams. We illustrate by three case studies the complete design methodology and validate the analytical models by comparing their predictions to those of detailed CFD and FE simulations. We employ the validated analytical models to perform Monte Carlo analyses to quantify, for box-like structures, how the uncertainty in input design variables propagates through to the expected maximum force and impulse. We present this information in the form of non-dimensional uncertainty maps. [ABSTRACT FROM AUTHOR]

Time reversal of waves is an intriguing wave property that underpins a breadth of applications in physics and engineering. Waves contain information about their sources and the media through which they propagate. Thus, time reversal of measured wave signals has the potential of localizing and characterizing wave sources and of inferring the properties of the medium. Herein, we experimentally demonstrate the time reversibility of acoustic waves propagating in water-filled viscoelastic high-density polyethylene (HDPE) pipes. Evidently, the two mechanisms that restrict time reversal are the stability of wave paths to perturbations and damping. Perturbations, however, are found to grow slowly in time (∼t1/2) and are not critical for the time reversal of waves. To evaluate the effect of damping, we perform an order of magnitude analysis on the non-reversible terms of the coupled waveguide momentum equations and derive a dimensionless time reversal parameter TR showing that damping develops linearly with time (i.e. TR ∼ t). Subsequently, we apply the TR parameter to our experiments and relevant experimental proofs from the literature to find that the time reversal of waves only holds for TR ∼ 1 or less; hence providing a criterion to estimate the range over which time reversal-based wave techniques and methodologies are valid. Finally, we discuss the various existing applications of time reversal in hydro-environmental research and engineering and anticipate that the presented work will stimulate further development. [ABSTRACT FROM AUTHOR]

An optical wave microphone, which is well designed based on Fraunhofer diffraction of a laser beam, is expected to be applied to various acoustic fields where conventional microphones cannot be used due to strong electric and/or magnetic field. The authors have developed this technique and applied it to detect discharge sounds emitted from plasmas such as micro plasma, gliding arc plasma and plasma jet. An improved optical wave microphone with regard to signal-to-noise ratio uses single mode optical fibers for laser transformation. In this study, detailed characteristics of the fiber-type optical wave microphone were evaluated according to the theory of the optical wave microphone. Furthermore, the fiber-type optical wave microphone was combined with computer tomography (CT). The fiber-type optical wave microphone CT succeeded to visualize and quantify 2-D acoustic field generated by an ultrasonic transducer, and the obtained sound pressure distribution showed good similarity to that measured with a condenser microphone. Furthermore, the technique was applied to surface barrier discharge with different applied voltage frequencies and the distribution of acoustic waves above the discharge was quantified. [ABSTRACT FROM AUTHOR]

A new concept of semi-compressible fluids is introduced for slightly compressible visco-elastic fluids (typically rather liquids than gasses) where mass density variations are negligible in some sense, while being directly controlled by pressure which is very small in comparison with the elastic bulk modulus. The physically consistent fully Eulerian models with specific dispersion of pressure-wave speed are devised. This contrasts to the so-called quasi-incompressible fluids which are described not physically consistently and, in fact, only approximate ideally incompressible ones in the limit. After surveying and modifying models for the quasi-incompressible fluids, we eventually devise some fully convective models complying with energy conservation and capturing phenomena as pressure-wave propagation with wave-length (and possibly also pressure) dependent velocity. [ABSTRACT FROM AUTHOR]

This paper focuses on an experimental procedure to localize multiple leaks in a nonhomogenous hydraulic pipeline system made up of three portions of two different materials. Then, an experimental setup originally designed for water hammer study was modified and adapted for leak detection using transients. Two leaks were made in some particular locations in the main pipe and a transient event through a rapid closure of a downstream valve was created. To mimic common practical issues that may be encountered, three main leakage cases were considered; a single leak, two simultaneous leaks and two successive leaks (i.e., one leak that appears followed by an abrupt appearance of a second leak after a period of time). Leaks were experimentally localized by analyzing obtained pressure signals in the excitation point. Results were validated through comparison with numerical ones obtained using the method of characteristics. Additionally, a novel formula to localize the second leak in a successive leaks scenario was presented and its accuracy was confirmed for our test case. Experimental techniques presented in this paper and performed on a test bench at lab scale can be extended and tested on large scale hydraulic pipeline systems. [ABSTRACT FROM AUTHOR]

The overset grid technique and an improved delayed detached-eddy simulation (IDDES) model were utilized to simulate the passage of a scaled-down prototype train through a tunnel. These simulations were verified through a moving-model test. To simulate the transient pressure and flow field generated when the train enters the tunnel at a speed of 350 km/h, a two-dimensional revolving-axisymmetric train/tunnel model (2D-RATTM) was proposed. The 2D-RATTM's ability to predict the transient pressure and pressure gradient in the tunnel was compared to the simulation data obtained from the prototype train/tunnel model in terms of prediction accuracy, simulation resource requirements, and potential engineering application. The results demonstrate that the 2D-RATTM achieves a prediction accuracy of over 91.3% for pressure amplitude and over 93.8% for the maximum pressure gradient in the tunnel. This confirms the reliability of the 2D-RATTM in predicting transient pressure and pressure gradient in the tunnel. Furthermore, the computational time required by the 2D-RATTM is reduced by 97.2%, leading to significant resource savings. This reduction in computational time is particularly beneficial for rapidly evaluating large-scale projects. Moreover, the prediction accuracy of pressure amplitude and maximum pressure gradient remains above 91.2% and 93.9% within a speed range of 300 km/h to 450 km/h. Similarly, when considering different train and tunnel parameters, such as tunnel length ranging from 330 m to 1000 m, the prediction accuracy of pressure amplitude and maximum pressure gradient remains above 91.3% and 93.9%. This demonstrates the feasibility of performing calculations using the 2D-RATTM under various train and tunnel configurations. These advancements position the 2D-RATTM as a highly valuable tool for engineering applications in future train-tunnel scenarios characterized by higher train speeds and longer tunnel lengths. • A two-dimensional revolving-axisymmetric train/tunnel model (2D-RATTM) is proposed to simulate the aerodynamics effect generated by the train entering the tunnel. • The prediction accuracy, simulation resource and the engineering application of the 2D-RATTM are compared with the prototype/tunnel simulation data. • The prediction accuracy of 2D-RATTM for tunnel pressure amplitude and maximum pressure gradient is above 91.3% and 93.8% respectively, and the CPU solution time is reduced by 97.2%. [ABSTRACT FROM AUTHOR]

Within the framework of Classical Continuum Thermomechanics, we consider an unsteady isothermal flow of a simple isotropic linear viscous fluid in the liquid state to investigate the transient flow conditions. Despite the attention paid to this problem by several research works, it seems that the understanding of turbulence in these flow conditions is controversial. We propose a dimensionless procedure that highlights some aspects related to the transition from viscous to turbulent flow which occurs when a finite amplitude pressure wave travels through the fluid. This kind of transition is demonstrated to be described by a (first) dimensionless number, which involves the bulk viscosity. Furthermore, in the turbulent flow regime, we show the role played by a (second) dimensionless number, which involves the turbulent bulk viscosity, in entropy production. Within the frame of the 1D model, we test the performance of the dimensionless procedure using experimental data on the pressure waves propagation in a long pipe (water hammer phenomenon). The obtained numerical results show good agreement with the experimental data. The results’ inspection confirms the predominant role of the turbulent bulk viscosity on energy dissipation processes.

Optimal operation and control of (variable-speed) pumped-storage power plants (PSPPs) is essential to meet the growing demands on the dynamics for the stabilization of power distribution grids with an increasing amount of renewable energy sources. Existing work on the control of PSPPs is typically based on rather simplified system models, in particular of the (long) pipeline system. In this article, a nonlinear model predictive control (NMPC) strategy is proposed, which enables fast closed-loop dynamics while keeping all system constraints, including the pressure constraints along the pipeline system. The control strategy is based on a physics-based model, which enables easy parameterization and application to other plant sizes or topologies. To ensure real-time capability of the model predictive control (MPC) strategy, a number of measures are outlined in this article. Finally, the feasibility of the proposed control strategy is demonstrated by detailed simulation studies. An accurate tracking for fast changing desired grid powers as well as a high robustness with respect to parameter uncertainties is demonstrated. [ABSTRACT FROM AUTHOR]

Traveling wave thermoacoustic-Stirling heat engine is a unique device that is used to convert heat energy to acoustic work. In this article, the thermoacoustic engine is modeled, manufactured and tested. The cyclic analysis is used to carry out the numerical analysis based on the Stirling cycle of the engine. This analysis has considered for study the physical property and characteristics of the regenerator matrix. The traveling acoustic wave produced from the prototype is measured using an audio-speaker as a linear alternator for extracting electrical power from acoustic power. The size and geometry of the regenerator mesh is defines the thermal penetration depth, pressure drop due to it, dead volume across the matrix and acoustic power produced. Hence, there is a need to optimize the mesh size for a given mesh material to maximize the power generated from the engine. The engine has tested with five combinations of mesh sizes. The results of the numerical analysis has shown that 50.1 W power is produced and the tested engine has developed 44.9 W electric-power with the thermal efficiency of 8.3% respectively for 304 wire mesh of SS having mesh size of 60 strands/inch. The results obtained from the numerical analysis and the experiments performed are presented in this paper.

Apart from peculiarities of the cerebral circulation, required to perfuse the brain with the subject erect, the principles established for function of the human systemic circulation (pulsatile flow at input and steady flow at output in capillaries) are identical to those established for other mammals. Assumption of the erect posture first as Homo erectus, then as Homo sapiens, conferred huge advantage to humans and led to command of the mammalian kingdom. But this required a circulation which could perfuse the brain securely against gravity in all positions of the body. This review covers what presently is known about the human cerebral circulation, and how such knowledge can be applied in some clinical conditions including development of dementia in older subjects, and in management of patients with elevation of intra-cranial pressure in younger subjects.

Apart from peculiarities of the cerebral circulation, required to perfuse the brain with the subject erect, the principles established for function of the human systemic circulation (pulsatile flow at input and steady flow at output in capillaries) are identical to those established for other mammals. Assumption of the erect posture first as Homo erectus, then as Homo sapiens, conferred huge advantage to humans and led to command of the mammalian kingdom. But this required a circulation which could perfuse the brain securely against gravity in all positions of the body. This review covers what presently is known about the human cerebral circulation, and how such knowledge can be applied in some clinical conditions including development of dementia in older subjects, and in management of patients with elevation of intra-cranial pressure in younger subjects. [ABSTRACT FROM AUTHOR]

Dynamics of pressure waves in a flat channel with a sloping boundary between bubbly and pure liquids is investigated. It is shown that, at the boundary between water–air mixture and water, reflection of waves incident on the boundary from the side of air–water mixture is analogous to reflection from a rigid wall, which leads to interference of waves. It is found that, with an increase in the volume content of bubbles and decrease in the bubble radius, the maximum wall pressure amplitude of the resulting wave increases. [ABSTRACT FROM AUTHOR]

The intended steady-state operation conditions of the International Fusion Materials Irradiation Facility—DEMO Oriented Neutron Source (IFMIF-DONES) target system are based on the D+ beam stationary running at full nominal power (5 MW). Nevertheless, critical situations can occur in the case of unavoidable sudden events like beam trips. The instantaneous variation in the heating power deposited in lithium when the beam is rapidly switched between ON- and OFF-states leads to thermal expansion, which is compensated by the compression of the target material, resulting in locally high pressures and a pressure wave propagating through the target toward the back wall. Besides the tensile stress of the back wall structure caused by shock pressure waves, undesirable cavitation may occur, when pressure waves are reflected leading to negative pressures. For this purpose, analytical and numerical thermohydraulic analyses of the effects generated in lithium during the beam-on/beam-off switches are performed. The pressure wave development inside the Li-target has been analyzed numerically with the computational fluid dynamics (CFD) code Star-CCM+. The simulation of the thermally induced pressure in the Li-target shows that for normal operation conditions, peak pressures of about 0, 3 MPa can be reached. In both “beam-on” and “beam-off” cases, a zone with a negative static pressure flow forms in the Li-target. The results obtained from the analytical and numerical analyses of the thermally induced pressure waves are discussed concerning potential cavitation and stability of the lithium free-surface flow. The simulation results served as input for the analysis of fatigue effects occurring in the target structure during sudden beam-on/beam-off events. [ABSTRACT FROM AUTHOR]

The present work investigates the details of unsteady flow behavior in a transonic centrifugal compressor with vaned diffuser. The analysis is based on solving three-dimensional, compressible, unsteady Navier-Stokes equations. The computational model is a high-compression ratio centrifugal compressor (4:1) consisting of an inlet duct, impeller, and diffuser vane. The hybrid scale-adaptive simulation (SAS) turbulent model is used to provide detailed flow information and characterize the transient flow structures within the compressor passages. A numerical sensitivity test is performed to validate the computational results in terms of pressure ratio and compressor efficiency. Instantaneous and mean flow field analyses are presented in the impeller and the vaned diffuser passages. Applying transient simulations, it is shown that the interaction between the pressure waves and the surface pressure of the diffuser blades leads to a pulsating behavior within the diffuser. Moreover, spectral analysis is evaluated to analyze the blade passing frequency (BPF) tonal noise as the main noise source of centrifugal compressors. In addition, the current SAS results are compared with those of the URANS-SST (shear stress transport) approach to show the ability of the SAS approach in the prediction of turbulent structures, where the SAS model leads to a much better resolution of the unsteady fluctuations. This study shows that the current SAS approach is promising in terms of the prediction of transient phenomena like LES, but offers a substantially reduced turn-around time. [ABSTRACT FROM AUTHOR]

Having unsteady flow in water supply systems due to the change from one stable state to another stable state is inevitable. On the other hand, over time, the various causes lead to the pipeline leakage or even a pipe fracture. So, with presence of leak, investigation of characteristics of unsteady flow that is an integral part of the hydraulic system will be of particular important. In current study, the fast unsteady flow that is one of the most damaging types of flow is simulated by laboratory considering leak in pipeline and with respect to that, the impact of leakage characteristics such as size and location of the leak on the hydraulic properties of unsteady flow will be evaluated. The experiments were carried on a tank, pipes and valve system that made of 63 mm polyethylene pipe with length of 47 meters and a height of 5 m for static water head in tank. A total of 3 discharges, 4 leakage diameters, 4 leakage positions and 2 fasten time of valve were tested that illustrate gradual valve fastening cannot show the leakage in pipeline system. Peak pressure drop in the first period of wave increases with increasing diameter and slope of the pressure drop caused by a leak in the first peak are faster for the leaks that nearer to the valve. Also, the pressure wave damping slope is steeper in the case of leakage with a greater diameter than leakage with a smaller diameter.

Linear alternators (LAs) are widely applied in many energy conversion systems based on pressure waves, to avoid linear to rotary conversion mechanisms. The control of the LA is the key element to maximise the system's electric power and efficiency. However, the LA resonant frequency cannot be accurately controlled by mechanical design due to parameter tolerance. Furthermore, the operating frequency is generally not strictly constant in real-time, making maximum power point tracking (MPPT) hard to achieve. Two MPPT strategies are proposed here to adjust the electronic stiffness amount in real time. They are hereafter referred to as symmetrical signal injection method and electronic stiffness perturbation method. The latter one is selected and validated via simulation studies.

Glass fiber/epoxy reinforced composite pipes are commonly used in the industry were circulation of extreme forced chemical fluids, industrial wastes and oil and natural gas transmission occurs. In oil and natural gas production, the heavy crude oil transporting pipe lines are exposed to unsteady pressure waves which generate rise and fall stress readings in the pipes. Computational fluid dynamic examination was implemented using Ansys 15.0 Fluent software to investigate the consequences of these pressure waves on some detailed joints in the pipes. Relating on the type of heavy crude oil being employed, the flow behaviour stated a significant degree of stress levels in evident attaching joints, triggering the joints to become delicate over a sustained phase of usage. In this analysis, the comparison among various pipe joints was done by using different materials, and the end result of the stress volume in the pipe joints was checked so that the life of the pipe joints can be optimized by the change of material. [ABSTRACT FROM AUTHOR]