Propagation Velocity Of Pressure Waves Research Articles

Simulation and Analysis of Pressure Waves in Flow Channels of Axial and Radial Gas Wave Ejectors

Introduction: As an efficient energy transfer technology, the gas wave ejector (GWE) holds several patents poised to address the challenges of low-carbon energy. These patents find applications in numerous fields. Traditional axial-flow GWE patents encounter limitations under certain application conditions, whereas radial-flow GWE patents offer an effective solution to these issues. However, the mechanisms behind the performance differences between these two types of GWEs have not yet been studied. Objective: Since pressure waves are central to energy transfer in wave rotors, this study analyzes the coupling effects of centrifugal forces and pressure waves. By examining the differences in pressure wave intensity and propagation velocity within two types of wave rotor channels, the mechanisms underlying the performance disparities are elucidated. Method: Fluent was utilized for numerical simulations, and Response Surface Methodology was employed to model the influence of various factors. Result and Discussion: It can be observed that the propagation velocity and intensity of pressure waves changed under the influence of centrifugal forces. The propagation velocities of S1 and E2, which propagate in the same direction as the fluid flow within the rotor, increase 9% and 32% respectively, whereas the propagation speed of E1, which propagates in the opposite direction of the fluid flow, decreases 15%. Regarding the intensity of each pressure wave, the coupling effect of centrifugal force resulted in an increase of 1.04 to 2.55 kPa. This paper is the first to fit a relational expression for the speed differential of pressure wave propagation within axial and radial flow channels, correlating the main pressure wave velocities (S1, E1, E2) with flow channel length, rotational speed, compression ratio, and expansion ratio, thus providing a reference for GWE design and analysis. Through analysis of variance and significance tests, it is evident that each parameter significantly contributes to the fitting degree of the pressure wave propagation velocity difference (p < 0.01). Furthermore, the inadequacy test (F-value=2.36~3.56) suggests a low level of discrepancy. Conclusion: The fundamental reason for the performance disparity between the two types of gas wave ejectors (GWE) lies in the discrepancies in pressure wave intensity and propagation velocity resulting from centrifugal force effects. Based on the fitted relationships, theoretical foundations can be provided for subsequent wave rotor design and performance analysis. For example, the differences in pressure wave propagation speed can inform the design and analysis of corresponding pressure ports.

Preliminary Test of Gas Wave Ejector in Coalbed Methane Well Site and Impact Analysis of Fluid Medium Characteristics on Its Pressure Port Design

Gas wave ejector (GWE) is an efficient energy conversion device which can recover and utilize excess pressure energy of high pressure fluid. It has significant application value in the sustainable development of energy resources, including the exploitation and transportation of natural gas. The first practical application test of GWE in the natural gas industry is completed in this study. The mechanisms and regulations of the effect of actual gas properties on the pressure port design of GWE were also investigated. The primary conclusions are as follows: the composition of working medium significantly affects the propagation velocity of pressure waves. The wave propagation velocity increases as methane purity (φCH4) rises. The equipment efficiency was decreased by up to 23% of the optimal value as a result of the variation in port position brought on by the increase in φCH4 from 0.7 to 1.0. The variation of working pressure ratio has a greater impact on the device performance than the pressure value when the pressure port design kept unchanged. The intake temperature fluctuation in the range of -30°C to 50°C has no obvious influence on the ideal port design. In the coal-bed methane well site industrial test, GWE accomplishes a recovery of low-pressure well by roughly 8.83 × 10 3 N m 3 / d , demonstrating its excellent ejection capacity. In addition, the variable speed test conducted under different working conditions shows that the equipment performance can be effectively enhanced by adjusting the rotation speed as the equipment structure remains unchanged with the changing working pressure/pressure ratio. In the field test range of this study, the increase of equipment ejection rate obtained by speed adjustment can rise up to 12% of the corresponding value at the designed rotation speed.

Investigation of fluid transients in a penstock attached to a Francis turbine rig using seismic interferometry

Pressure fluctuations in hydropower plants contribute to fatigue loads. Pressure pulsations generated by a reaction turbine will create fluid transients in the attached system which can increase the load on structural parts if resonance occurs. Several factors govern transients in a pipe system where the main parameters are the length between reflection points and the propagation velocity. This paper investigates how to find the propagation velocity of pressure waves measured in the penstock at the Hydropower Laboratory at NTNU by applying techniques from seismic interferometry. A simple 1-D model has been developed using the method of characteristics to compare the experimental results to a known system. Seismic interferometry is primarily used in academic and research settings, the basic principle is to obtain the Green’s function between measured signals. The results from the experimental data and simulations are promising, but further research is needed to optimize both data acquisition and post processing.

A Small Leak Localization Method for Oil Pipelines Based on Information Fusion

When an oil pipeline has small leaks, the change of the sound velocity of an ultrasonic signal cannot be easily detected. Based on the method of characteristics theory, the leakage occurrence mechanism of a pipeline and the propagation mechanism of the sound velocity of the ultrasonic signal along the pipeline were studied. Additionally, the computational models of generating the sound velocity of the ultrasonic signal induced by pipeline leakage and calculating the propagation attenuation of the ultrasonic wave along the pipeline were established. A small leak localization method for pipelines based on information fusion is proposed, which is a combination of the sound velocity of the ultrasonic and flow rate signals. First, the fusion signals are extracted from the signal inflection point using a modified cross-correlation to determine the time difference of the fusion signal changes at the ends of the pipeline; then, the leak position is calculated based on the information of the pipeline length and the negative pressure wave propagation velocity. Since the change of the information fusion signal induced by a small leak is larger than the change of the sound velocity of the ultrasonic signal and the change of pressure signal, the proposed method can be used to locate a small leak in a pipeline. By analyzing the acquired data of a small leak in an experimental pipeline, the results show that the proposed method can quickly and effectively locate small leaks.

Об алгоритме идентификации скорости распространения возмущений в магистральном трубопроводе и особенностях его реализации

Об алгоритме идентификации скорости распространения возмущений в магистральном трубопроводе и особенностях его реализации

급수용 급속공기밸브의 성능특성에 관한 실험적 연구

When the fluid energy convert into kinetic energy due to water hammer, the propagation velocity of pressure wave appear. The propagation velocity of pressure wave(1050 m/s) of very fast could be damage to the pipeline system. If the occurrence of water hammer is due to down-pressure, the faster the air exhaust or supply device is needed. it is high Speed Air Valve. In this paper, Each 3.12, 3.13, 3.72, <TEX>$3.74kg/cm^2$</TEX> pipeline pressure were setting, and then executed pressure rapid drop for obtaining a high Speed Air Valve Operating time and pressure change data. the result was that pipe line pressure stabilization time were each 0.98, 1, 1.22, 1.25 sec. In other words, that pressure drop experimental results pipe line pressure was equal to atmospheric pressure without negative pressure After about one second. The study result would be useful to pipe line system stability design because this data could be foresee pressure stabilization time.

Measurement of bulk modulus of elasticity of dense pastes and its effects on flow rate in long pipeline

The amount of dense pastes, such as dewatered coal washing tailing, red mud, calcium carbide sludge and sewage sludge, is enormous and continues to grow rapidly. More engineering long pipelines with large diameter are employed to meet the urgent needs of their disposition, which results to serious reversed flow and strong vibration to the pipeline system. Both the problems have close relationship with the elastic parameters of the delivered paste. This paper presents a test undertaken for finding the bulk modulus of elasticity of the coal tailing. The test was undertaken on a long engineering pipeline for transporting coal slime paste based on the wave velocity method. By selecting suitable feature points in the pressure curves, the pressure wave propagation velocity in the coal slime was tested accurately. By the relationship between the elastic modulus of the paste and the wave velocity, the composite modulus of the coal slime and pipeline, and the true bulk modulus of the paste were both calculated. By resulting in serious reversed flow and reducing the effective piston stroke of the pump, the elastic recovery of the coal slime has an important effect on the actual flow rate. The variation characteristics of the pressure curves have proved that the measurement is an easy and practical method for finding the elastic modulus of dense pastes.

An Improved Negative Pressure Wave Method for Natural Gas Pipeline Leak Location Using FBG Based Strain Sensor and Wavelet Transform

Methods that more quickly locate leakages in natural gas pipelines are urgently required. In this paper, an improved negative pressure wave method based on FBG based strain sensors and wavelet analysis is proposed. This method takes into account the variation in the negative pressure wave propagation velocity and the gas velocity variation, uses the traditional leak location formula, and employs Compound Simpson and Dichotomy Searching for solving this formula. In addition, a FBG based strain sensor instead of a traditional pressure sensor was developed for detecting the negative pressure wave signal produced by leakage. Unlike traditional sensors, FBG sensors can be installed anywhere along the pipeline, thus leading to high positioning accuracy through more frequent installment of the sensors. Finally, a wavelet transform method was employed to locate the pressure drop points within the FBG signals. Experiment results show good positioning accuracy for natural gas pipeline leakage, using this new method.

On the effect of temperature and velocity relaxation in two-phase flow models

We study a two-phase pipe flow model with relaxation terms in the momentum and energy equations, driving the model towards dynamic and thermal equilibrium. These equilibrium states are characterized by the velocities and temperatures being equal in each phase. For each of these relaxation processes, we consider the limits of zero and infinite relaxation times. By expanding on previously established results, we derive a formulation of the mixture sound velocity for the thermally relaxed model. This allows us to directly prove a subcharacteristic condition; each level of equilibrium assumption imposed reduces the propagation velocity of pressure waves. Furthermore, we show that each relaxation procedure reduces the mixture sound velocity with a factor that is independent of whether the other relaxation procedure has already been performed. Numerical simulations indicate that thermal relaxation in the two-fluid model has negligible impact on mass transport dynamics. However, the velocity difference of sonic propagation in the thermally relaxed and unrelaxed two-fluid models may significantly affect practical simulations.

CFD simulation of pressure fluctuation characteristics in the gas-solid fluidized bed: Comparisons with experiments

A simple hydrodynamic model based on two-fluid theory, taking into account the effect of discrete particles on both the gas- and solid-phase momentum equations, was used to numerically investigate the pressure fluctuation characteristics in a gas-solid fluidized bed with the aid of CFX 4.4, a commercial CFD software package, by adding user-defined Fortran subroutines. Numerical simulations together with typical experimental measurements show that pressure fluctuations originate above the distributor when a gas pulse is injected into the fluidized bed. The pressure above the bubble gradually increases due to the presence of a rising bubble. When the bubble passes through the bed surface, the pressure near the bed surface gradually decreases to a lower value. Moreover, the pressure signals in the bubbling fluidized beds show obviously periodic characteristics. The major frequency of pressure fluctuations at the same vertical position is affected slightly by the operating gas velocity, and the amplitude of pressure fluctuations is related to both the operating gas velocity and the vertical height. In this study, the influence of the operating gas velocity on the pressure wave propagation velocity can be ignored, and only two peak frequencies in the power spectrum of the pressure fluctuations are observed which are associated with the bubble formation above the distributor and its eruption at the bed surface.

Friction relaxation model for fast transient flows application to water hammer in two-phase flow – The WAHA code

The paper deals with the problem of the wall shear stress during rapid transient 1D flows in a piping system caused by water hammers in two-phase flow induced by a fast valve closure. The evolution of the transient wall shear stress is interpreted in terms of two steps. The first step is a sudden and dramatic change of the wall shear stress due to the passage of the pressure wave. The second step is a relaxation process of the shear stress which is modeled from the Extended Irreversible Thermodynamics theory. The friction relaxation model (FRM) presented in the first part of this paper describes both steps of the evolution of the wall shear stress during water hammers. The second part of the paper deals with the application of the FRM model as a closure law in the WAHA code. The main purpose of the WAHA code is to predict various situations relative to single- and two-phase water hammer transients in piping systems. The last part of the paper deals with the simulation of several cases from the UMSICHT databank using the adapted WAHA computer code with the FRM model. The results of these simulations are systematically compared with the experimental data. It is concluded that the new FRM model has a clear effect on water hammer pressure wave damping and on the pressure wave propagation velocity.

Visualization of Wave Rotor Inner Flow Dynamics

The design of a wave rotor requires an understanding of the pressure wave dynamics in the cells (rotor passages). The present paper describes a two-dimensional numerical simulation and an experimental visualization of the wave rotor compression process. First, a unique experimental apparatus with fixed cells and rotating ports was constructed for the visualization and direct measurements; this arrangement is opposite to the conventional setup. Next, experimental and numerical results were compared to verify the simulation modeling, particularly with regard to the propagation velocity of pressure waves in the cells. Last, the effects of gradually opening the cell to the ports and leakage through the clearance, which are considered to be dominant factors in the wave rotor operation, on the pressure wave dynamics were carefully investigated. The results showed that the gradual passage opening greatly influences the primary shock wave, whereas leakage mostly influences the reflected shock wave. Moreover, it was revealed that the leakage generates an extra pressure wave during the compression process due to the interaction between adjacent cells.

Propagation of weak pressure waves against two parallel subsonic streams

In this paper, the characteristics of a pressure wave propagating against two parallel subsonic streams in a constant-area straight duct are investigated by one-dimensional analysis, two-dimensional numerical simulation, and experiments. Computations have been carried out by the two-dimensional Euler Equations using the Chakravarthy-Osher-type TVD scheme. Optical observations by the schlieren method as well as wall pressure measurements have been performed to clarify both the structure and the propagation velocity of pressure waves. The results show that the pressure wave propagating against the streams changes into a bifurcated pressure wave and the bifurcation occurs in the low speed streams. It is also found that the propagation velocity of the pressure wave obtained by the analysis and computation agrees well with the present experimental data.

ウェーブロータ内部流動の可視化

The design of a wave rotor requires an understanding of the pressure wave dynamics in the rotor passages. The present paper describes a two-dimensional numerical simulation and an experimental visualization of the wave rotor compression process. First, a unique experimental apparatus with fixed cells and rotating ports was constructed for visualization and direct measurements; this arrangement is opposite to the conventional setup. Next, experimental and numerical results were compared to verify the simulation modelling, particularly with regard to the propagation velocity of pressure waves in the passages. Lastly, the effects of gradually opening the passage to the ports and leakage through the clearance, which are considered to be dominant factors in wave rotor operation, on the pressure wave dynamics were carefully investigated. The results showed that the gradual passage opening greatly influences the primary shock wave, whereas the leakage mostly influences the secondary (reflected) shock wave. Moreover, it was revealed that the leakage generates an extra pressure wave during the compression process due to the interaction between adjacent passages.

Pressure wave propagation in air-water bubbly and slug flow

Related to nuclear reactor safety problems, such as the loss of coolant accident caused by some small crevasses in nuclear reactor, choked flows after postulated breaks of hot and cold legs of pressurized water reactors and the boiling flow instability in parallel channels, the characteristics of pressure wave propagation were investigated experimentally for the air-water bubbly and slug two-phase flow in a vertical pipe. Pressure wave was generated from the small pressure disturbance by the up-and-down movement of piston in the test section. Air void fraction was up to 0.7 and superficial liquid velocity was up to 1.5 m/s as experimental conditions. The experimental results show that the pressure wave propagation velocity in bubbly flow decreases acutely with the increase of air void fraction from 0 to 0.05. In slug flow, it is constant when the air void fraction is less than 0.5 but increases gradually when the void fraction increases beyond 0.5. The attenuation coefficient of pressure wave increases with the increase of air void fraction in bubbly flow. The dependency of pressure wave propagation velocity on angle frequency ω in air-water flow shows the dispersion characteristic. The propagation velocity and attenuation coefficient increases gradually with the increase of angle frequency. However, the increase vanishes slowly as the angle frequency reaches 250 Hz in bubbly flow. The propagation of pressure wave in bubbly flow is independent of the superficial velocity of fluids in the range of experiment.

Cold model characterisation of a fluidised bed catalytic reactor by means of instantaneous pressure measurements

The analysis of instantaneous pressure fluctuations is utilised in a cold modelling study of a pilot scale fluidised bed catalytic reactor for ethane oxychlorination. It is demonstrated that the fluid dynamic behaviour of a cold model of this fine particle (Geldart group A) system is well characterised by the frequency spectrum, the standard deviation and the cross-correlation of pressure signals detected at different locations within the bed and in the freeboard. The influence of operating parameters, such as gas flow rate, initial bed height, reactor configuration (internals) and average value of the local pressure, is investigated, and a comparison is made with the features exhibited by Geldart group B systems (fluidised bed combustors) for which the same diagnostic techniques have been applied. Finally, the applicability to fine particle suspensions of literature correlations for dominant frequency and propagation velocity of pressure waves is discussed with reference to the combined influence of the eruption of many small bubbles at the bed surface, and the compressibility of the gas contained within the particle-bed interstices.

Two-phase flow of liquid-gas in diesel fuel injection system and their effect on engine performances

In this paper, by using high-speed camera, CCD camera, signal and graph acquisition system, and other experimental instruments, investigation on liquid-gas two-phase flow in diesel fuel injection system and their effect on engine performances were made. Emerging and bursting of cavitation in the cavity above pump delivery valve, in injection pipe, and in fuel trough of injector of the fuel injection system were observed and mechanism of cavitation were discussed. Effects of liquid-gas two-phase flow on propagation velocity of pressure wave of the system and on irregular injection were analyzed. Two types of cavitation, long living time cavitation and short living time cavitation, in the cavity above pump delivery valve of diesel fuel injection system were observed.

Pressure wave propagation by gas expansion in a high vacuum tube

In this article we describe an unsteady tube flow model which accounts for the effect of contracted flow around the entrance orifice of the tube which was developed with the aim of preventing vacuum hazards at scientific experimental facilities. Setting an atmospheric pressure drop between the outside and inside of the vacuum tube makes the model applicable to high vacuum, although the model is based on continuous fluid dynamics. We installed an orifice on the inlet end of the tube in the model, and investigated the orifice aperture effect on the propagation velocity of pressure waves.

Origin, propagation and attenuation of pressure waves in gas—solid fluidized beds

Recently reported results on the origin, propagation and attenuation of pressure waves in bubbling gas—solid fluidized beds are re-evaluated and the results are compared with additional experiments reported here. It is found that the measured pressure fluctuations are a result of slow and fast propagating pressure waves. Pressure waves with high propagation velocities (> 10 m/s) are unambiguously identified as compression waves, which move upwards and downwards. Upward moving compression waves originate from gas bubble formation and gas bubble coalescence. The amplitude of upward moving pressure waves is linearly dependent on the distance to the bed surface. Downward moving compression waves are caused by gas bubble eruptions at the fluidized bed surface, bubble coalescence and by changes in bed voidage. In this case the pressure wave amplitude is independent of the distance to the bed surface. Pressure waves with propagation velocities of less than 2 m/s are caused by rising gas bubbles. These pressure waves move upwards only, with an amplitude proportional to the bubble size. The average wave propagation velocity measured in a freely bubbling bed is lower than that predicted from the pseudo-homogeneous compressible wave theory owing to the presence of slowly rising gas bubbles. The average propagation velocity of pressure waves in a gas—solid circulating fluidized bed is adequately described as a function of local voidage by pseudo-homogeneous compressible wave theory. At low voidages in the bottom of the riser, the propagation velocity is lowered by the presence of gas bubbles or large gas voids.

Measurements of the speed of sound in air-water flows

Abstract Pressure transducer measurements, recorded while calibrating two conductivity-based, void fraction meters, show how the propagation velocity of pressure waves in bubbly air-water flows varies with void fraction. The results for void fractions between 0 and 0.5 indicate that, as expected, the propagation velocities in an air-water mixture are considerably lower than the speed of sound in either component; they agree well with prediction methods based on the mixture density and bulk modulus.